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= How to use the QAPI code generator =
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Copyright IBM Corp. 2011
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Copyright (C) 2012-2016 Red Hat, Inc.
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This work is licensed under the terms of the GNU GPL, version 2 or
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later. See the COPYING file in the top-level directory.
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== Introduction ==
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2011-07-19 21:50:46 +02:00
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QAPI is a native C API within QEMU which provides management-level
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functionality to internal and external users. For external
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users/processes, this interface is made available by a JSON-based wire
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format for the QEMU Monitor Protocol (QMP) for controlling qemu, as
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well as the QEMU Guest Agent (QGA) for communicating with the guest.
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The remainder of this document uses "Client JSON Protocol" when
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referring to the wire contents of a QMP or QGA connection.
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To map Client JSON Protocol interfaces to the native C QAPI
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implementations, a JSON-based schema is used to define types and
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function signatures, and a set of scripts is used to generate types,
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signatures, and marshaling/dispatch code. This document will describe
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how the schemas, scripts, and resulting code are used.
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2011-07-19 21:50:46 +02:00
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== QMP/Guest agent schema ==
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A QAPI schema file is designed to be loosely based on JSON
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(http://www.ietf.org/rfc/rfc7159.txt) with changes for quoting style
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and the use of comments; a QAPI schema file is then parsed by a python
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code generation program. A valid QAPI schema consists of a series of
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top-level expressions, with no commas between them. Where
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dictionaries (JSON objects) are used, they are parsed as python
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OrderedDicts so that ordering is preserved (for predictable layout of
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generated C structs and parameter lists). Ordering doesn't matter
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between top-level expressions or the keys within an expression, but
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does matter within dictionary values for 'data' and 'returns' members
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of a single expression. QAPI schema input is written using 'single
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quotes' instead of JSON's "double quotes" (in contrast, Client JSON
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Protocol uses no comments, and while input accepts 'single quotes' as
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an extension, output is strict JSON using only "double quotes"). As
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in JSON, trailing commas are not permitted in arrays or dictionaries.
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Input must be ASCII (although QMP supports full Unicode strings, the
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QAPI parser does not). At present, there is no place where a QAPI
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schema requires the use of JSON numbers or null.
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Comments are allowed; anything between an unquoted # and the following
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newline is ignored. Although there is not yet a documentation
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generator, a form of stylized comments has developed for consistently
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documenting details about an expression and when it was added to the
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schema. The documentation is delimited between two lines of ##, then
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the first line names the expression, an optional overview is provided,
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then individual documentation about each member of 'data' is provided,
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and finally, a 'Since: x.y.z' tag lists the release that introduced
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the expression. Optional members are tagged with the phrase
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'#optional', often with their default value; and extensions added
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after the expression was first released are also given a '(since
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x.y.z)' comment. For example:
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##
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# @BlockStats:
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#
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# Statistics of a virtual block device or a block backing device.
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#
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# @device: #optional If the stats are for a virtual block device, the name
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# corresponding to the virtual block device.
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#
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# @stats: A @BlockDeviceStats for the device.
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#
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# @parent: #optional This describes the file block device if it has one.
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#
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# @backing: #optional This describes the backing block device if it has one.
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# (Since 2.0)
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#
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# Since: 0.14.0
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##
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{ 'struct': 'BlockStats',
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'data': {'*device': 'str', 'stats': 'BlockDeviceStats',
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'*parent': 'BlockStats',
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'*backing': 'BlockStats'} }
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The schema sets up a series of types, as well as commands and events
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that will use those types. Forward references are allowed: the parser
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scans in two passes, where the first pass learns all type names, and
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the second validates the schema and generates the code. This allows
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the definition of complex structs that can have mutually recursive
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types, and allows for indefinite nesting of Client JSON Protocol that
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satisfies the schema. A type name should not be defined more than
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once. It is permissible for the schema to contain additional types
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not used by any commands or events in the Client JSON Protocol, for
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the side effect of generated C code used internally.
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There are seven top-level expressions recognized by the parser:
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'include', 'command', 'struct', 'enum', 'union', 'alternate', and
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'event'. There are several groups of types: simple types (a number of
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built-in types, such as 'int' and 'str'; as well as enumerations),
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complex types (structs and two flavors of unions), and alternate types
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(a choice between other types). The 'command' and 'event' expressions
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can refer to existing types by name, or list an anonymous type as a
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dictionary. Listing a type name inside an array refers to a
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single-dimension array of that type; multi-dimension arrays are not
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directly supported (although an array of a complex struct that
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contains an array member is possible).
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Types, commands, and events share a common namespace. Therefore,
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generally speaking, type definitions should always use CamelCase for
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user-defined type names, while built-in types are lowercase. Type
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definitions should not end in 'Kind', as this namespace is used for
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creating implicit C enums for visiting union types, or in 'List', as
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this namespace is used for creating array types. Command names,
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and member names within a type, should be all lower case with words
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separated by a hyphen. However, some existing older commands and
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complex types use underscore; when extending such expressions,
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consistency is preferred over blindly avoiding underscore. Event
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names should be ALL_CAPS with words separated by underscore. Member
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qapi: Reserve 'q_*' and 'has_*' member names
c_name() produces names starting with 'q_' when protecting a
dictionary member name that would fail to directly compile, but
in doing so can cause clashes with any member name already
beginning with 'q-' or 'q_'. Likewise, we create a C name 'has_'
for any optional member that can clash with any member name
beginning with 'has-' or 'has_'.
Technically, rather than blindly reserving the namespace,
we could try to complain about user names only when an actual
collision occurs, or even teach c_name() how to munge names
to avoid collisions. But it is not trivial, especially when
collisions can occur across multiple types (such as via
inheritance or flat unions). Besides, no existing .json
files are trying to use these names. So it's easier to just
outright forbid the potential for collision. We can always
relax things in the future if a real need arises for QMP to
express member names that have been forbidden here.
'has_' only has to be reserved for struct/union member names,
while 'q_' is reserved everywhere (matching the fact that
only members can be optional, while we use c_name() for munging
both members and entities). Note that we could relax 'q_'
restrictions on entities independently from member names; for
example, c_name('qmp_' + 'unix') would result in a different
function name than our current 'qmp_' + c_name('unix').
Update and add tests to cover the new error messages.
Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1445898903-12082-6-git-send-email-eblake@redhat.com>
[Consistently pass protect=False to c_name(); commit message tweaked
slightly]
Signed-off-by: Markus Armbruster <armbru@redhat.com>
2015-10-26 23:34:44 +01:00
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names cannot start with 'has-' or 'has_', as this is reserved for
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tracking optional members.
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Any name (command, event, type, member, or enum value) beginning with
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"x-" is marked experimental, and may be withdrawn or changed
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incompatibly in a future release. All names must begin with a letter,
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and contain only ASCII letters, digits, dash, and underscore. There
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are two exceptions: enum values may start with a digit, and any
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extensions added by downstream vendors should start with a prefix
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matching "__RFQDN_" (for the reverse-fully-qualified-domain-name of
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the vendor), even if the rest of the name uses dash (example:
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__com.redhat_drive-mirror). Names beginning with 'q_' are reserved
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for the generator: QMP names that resemble C keywords or other
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problematic strings will be munged in C to use this prefix. For
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example, a member named "default" in qapi becomes "q_default" in the
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generated C code.
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In the rest of this document, usage lines are given for each
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expression type, with literal strings written in lower case and
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placeholders written in capitals. If a literal string includes a
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prefix of '*', that key/value pair can be omitted from the expression.
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For example, a usage statement that includes '*base':STRUCT-NAME
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means that an expression has an optional key 'base', which if present
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must have a value that forms a struct name.
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=== Built-in Types ===
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The following types are predefined, and map to C as follows:
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Schema C JSON
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str char * any JSON string, UTF-8
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number double any JSON number
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int int64_t a JSON number without fractional part
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that fits into the C integer type
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int8 int8_t likewise
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int16 int16_t likewise
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int32 int32_t likewise
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int64 int64_t likewise
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uint8 uint8_t likewise
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uint16 uint16_t likewise
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uint32 uint32_t likewise
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uint64 uint64_t likewise
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size uint64_t like uint64_t, except StringInputVisitor
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accepts size suffixes
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bool bool JSON true or false
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any QObject * any JSON value
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qapi: Convert QType into QAPI built-in enum type
What's more meta than using qapi to define qapi? :)
Convert QType into a full-fledged[*] builtin qapi enum type, so
that a subsequent patch can then use it as the discriminator
type of qapi alternate types. Fortunately, the judicious use of
'prefix' in the qapi definition avoids churn to the spelling of
the enum constants.
To avoid circular definitions, we have to flip the order of
inclusion between "qobject.h" vs. "qapi-types.h". Back in commit
28770e0, we had the latter include the former, so that we could
use 'QObject *' for our implementation of 'any'. But that usage
also works with only a forward declaration, whereas the
definition of QObject requires QType to be a complete type.
[*] The type has to be builtin, rather than declared in
qapi/common.json, because we want to use it for alternates even
when common.json is not included. But since it is the first
builtin enum type, we have to add special cases to qapi-types
and qapi-visit to only emit definitions once, even when two
qapi files are being compiled into the same binary (the way we
already handled builtin list types like 'intList'). We may
need to revisit how multiple qapi files share common types,
but that's a project for another day.
Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1449033659-25497-4-git-send-email-eblake@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
2015-12-02 06:20:47 +01:00
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QType QType JSON string matching enum QType values
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2014-05-07 20:46:15 +02:00
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=== Includes ===
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Usage: { 'include': STRING }
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The QAPI schema definitions can be modularized using the 'include' directive:
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{ 'include': 'path/to/file.json' }
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The directive is evaluated recursively, and include paths are relative to the
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file using the directive. Multiple includes of the same file are
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idempotent. No other keys should appear in the expression, and the include
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value should be a string.
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As a matter of style, it is a good idea to have all files be
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self-contained, but at the moment, nothing prevents an included file
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from making a forward reference to a type that is only introduced by
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an outer file. The parser may be made stricter in the future to
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prevent incomplete include files.
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=== Struct types ===
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Usage: { 'struct': STRING, 'data': DICT, '*base': STRUCT-NAME }
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2016-02-18 07:48:16 +01:00
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A struct is a dictionary containing a single 'data' key whose value is
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a dictionary; the dictionary may be empty. This corresponds to a
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struct in C or an Object in JSON. Each value of the 'data' dictionary
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must be the name of a type, or a one-element array containing a type
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name. An example of a struct is:
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{ 'struct': 'MyType',
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'data': { 'member1': 'str', 'member2': 'int', '*member3': 'str' } }
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The use of '*' as a prefix to the name means the member is optional in
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the corresponding JSON protocol usage.
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The default initialization value of an optional argument should not be changed
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between versions of QEMU unless the new default maintains backward
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compatibility to the user-visible behavior of the old default.
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With proper documentation, this policy still allows some flexibility; for
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example, documenting that a default of 0 picks an optimal buffer size allows
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one release to declare the optimal size at 512 while another release declares
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the optimal size at 4096 - the user-visible behavior is not the bytes used by
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the buffer, but the fact that the buffer was optimal size.
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On input structures (only mentioned in the 'data' side of a command), changing
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from mandatory to optional is safe (older clients will supply the option, and
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newer clients can benefit from the default); changing from optional to
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mandatory is backwards incompatible (older clients may be omitting the option,
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and must continue to work).
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On output structures (only mentioned in the 'returns' side of a command),
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changing from mandatory to optional is in general unsafe (older clients may be
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expecting the member, and could crash if it is missing), although it
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can be done if the only way that the optional argument will be omitted
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is when it is triggered by the presence of a new input flag to the
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command that older clients don't know to send. Changing from optional
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to mandatory is safe.
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A structure that is used in both input and output of various commands
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must consider the backwards compatibility constraints of both directions
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of use.
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A struct definition can specify another struct as its base.
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In this case, the members of the base type are included as top-level members
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of the new struct's dictionary in the Client JSON Protocol wire
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format. An example definition is:
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{ 'struct': 'BlockdevOptionsGenericFormat', 'data': { 'file': 'str' } }
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{ 'struct': 'BlockdevOptionsGenericCOWFormat',
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'base': 'BlockdevOptionsGenericFormat',
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'data': { '*backing': 'str' } }
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An example BlockdevOptionsGenericCOWFormat object on the wire could use
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both members like this:
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{ "file": "/some/place/my-image",
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"backing": "/some/place/my-backing-file" }
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2013-07-16 13:17:27 +02:00
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=== Enumeration types ===
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Usage: { 'enum': STRING, 'data': ARRAY-OF-STRING }
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{ 'enum': STRING, '*prefix': STRING, 'data': ARRAY-OF-STRING }
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An enumeration type is a dictionary containing a single 'data' key
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|
|
whose value is a list of strings. An example enumeration is:
|
2011-07-19 21:50:46 +02:00
|
|
|
|
|
|
|
{ 'enum': 'MyEnum', 'data': [ 'value1', 'value2', 'value3' ] }
|
|
|
|
|
2015-05-04 17:04:59 +02:00
|
|
|
Nothing prevents an empty enumeration, although it is probably not
|
|
|
|
useful. The list of strings should be lower case; if an enum name
|
|
|
|
represents multiple words, use '-' between words. The string 'max' is
|
|
|
|
not allowed as an enum value, and values should not be repeated.
|
|
|
|
|
2015-08-26 15:21:20 +02:00
|
|
|
The enum constants will be named by using a heuristic to turn the
|
|
|
|
type name into a set of underscore separated words. For the example
|
|
|
|
above, 'MyEnum' will turn into 'MY_ENUM' giving a constant name
|
|
|
|
of 'MY_ENUM_VALUE1' for the first value. If the default heuristic
|
2016-03-03 17:16:46 +01:00
|
|
|
does not result in a desirable name, the optional 'prefix' member
|
2015-08-26 15:21:20 +02:00
|
|
|
can be used when defining the enum.
|
|
|
|
|
2015-05-04 17:05:35 +02:00
|
|
|
The enumeration values are passed as strings over the Client JSON
|
|
|
|
Protocol, but are encoded as C enum integral values in generated code.
|
|
|
|
While the C code starts numbering at 0, it is better to use explicit
|
2015-05-04 17:04:59 +02:00
|
|
|
comparisons to enum values than implicit comparisons to 0; the C code
|
|
|
|
will also include a generated enum member ending in _MAX for tracking
|
|
|
|
the size of the enum, useful when using common functions for
|
|
|
|
converting between strings and enum values. Since the wire format
|
|
|
|
always passes by name, it is acceptable to reorder or add new
|
2015-05-04 17:05:35 +02:00
|
|
|
enumeration members in any location without breaking clients of Client
|
|
|
|
JSON Protocol; however, removing enum values would break
|
2016-03-03 17:16:46 +01:00
|
|
|
compatibility. For any struct that has a member that will only contain
|
|
|
|
a finite set of string values, using an enum type for that member is
|
|
|
|
better than open-coding the member to be type 'str'.
|
2015-05-04 17:04:59 +02:00
|
|
|
|
|
|
|
|
2013-07-16 13:17:27 +02:00
|
|
|
=== Union types ===
|
|
|
|
|
2015-05-04 17:04:59 +02:00
|
|
|
Usage: { 'union': STRING, 'data': DICT }
|
2016-03-17 23:48:39 +01:00
|
|
|
or: { 'union': STRING, 'data': DICT, 'base': STRUCT-NAME-OR-DICT,
|
2015-05-04 17:04:59 +02:00
|
|
|
'discriminator': ENUM-MEMBER-OF-BASE }
|
2013-07-16 13:17:27 +02:00
|
|
|
|
2015-05-04 17:04:59 +02:00
|
|
|
Union types are used to let the user choose between several different
|
2015-05-04 17:05:12 +02:00
|
|
|
variants for an object. There are two flavors: simple (no
|
2016-02-18 07:48:16 +01:00
|
|
|
discriminator or base), and flat (both discriminator and base). A union
|
2015-05-04 17:05:12 +02:00
|
|
|
type is defined using a data dictionary as explained in the following
|
2016-02-18 07:48:16 +01:00
|
|
|
paragraphs. The data dictionary for either type of union must not
|
|
|
|
be empty.
|
2013-07-16 13:17:27 +02:00
|
|
|
|
2015-05-04 17:04:59 +02:00
|
|
|
A simple union type defines a mapping from automatic discriminator
|
|
|
|
values to data types like in this example:
|
2013-07-16 13:17:27 +02:00
|
|
|
|
2016-03-17 23:48:38 +01:00
|
|
|
{ 'struct': 'BlockdevOptionsFile', 'data': { 'filename': 'str' } }
|
|
|
|
{ 'struct': 'BlockdevOptionsQcow2',
|
|
|
|
'data': { 'backing': 'str', '*lazy-refcounts': 'bool' } }
|
2013-07-16 13:17:27 +02:00
|
|
|
|
2016-03-17 23:48:38 +01:00
|
|
|
{ 'union': 'BlockdevOptionsSimple',
|
|
|
|
'data': { 'file': 'BlockdevOptionsFile',
|
|
|
|
'qcow2': 'BlockdevOptionsQcow2' } }
|
2013-07-16 13:17:27 +02:00
|
|
|
|
2015-05-04 17:05:35 +02:00
|
|
|
In the Client JSON Protocol, a simple union is represented by a
|
2016-03-03 17:16:46 +01:00
|
|
|
dictionary that contains the 'type' member as a discriminator, and a
|
|
|
|
'data' member that is of the specified data type corresponding to the
|
2015-05-04 17:05:35 +02:00
|
|
|
discriminator value, as in these examples:
|
2013-07-16 13:17:27 +02:00
|
|
|
|
2016-03-17 23:48:38 +01:00
|
|
|
{ "type": "file", "data": { "filename": "/some/place/my-image" } }
|
|
|
|
{ "type": "qcow2", "data": { "backing": "/some/place/my-image",
|
|
|
|
"lazy-refcounts": true } }
|
2013-07-16 13:17:27 +02:00
|
|
|
|
2015-05-04 17:04:59 +02:00
|
|
|
The generated C code uses a struct containing a union. Additionally,
|
|
|
|
an implicit C enum 'NameKind' is created, corresponding to the union
|
|
|
|
'Name', for accessing the various branches of the union. No branch of
|
|
|
|
the union can be named 'max', as this would collide with the implicit
|
|
|
|
enum. The value for each branch can be of any type.
|
2013-07-16 13:17:27 +02:00
|
|
|
|
2016-03-17 23:48:39 +01:00
|
|
|
A flat union definition avoids nesting on the wire, and specifies a
|
|
|
|
set of common members that occur in all variants of the union. The
|
|
|
|
'base' key must specifiy either a type name (the type must be a
|
|
|
|
struct, not a union), or a dictionary representing an anonymous type.
|
|
|
|
All branches of the union must be complex types, and the top-level
|
|
|
|
members of the union dictionary on the wire will be combination of
|
|
|
|
members from both the base type and the appropriate branch type (when
|
|
|
|
merging two dictionaries, there must be no keys in common). The
|
|
|
|
'discriminator' member must be the name of a non-optional enum-typed
|
|
|
|
member of the base struct.
|
2013-07-16 13:17:27 +02:00
|
|
|
|
2015-05-04 17:04:59 +02:00
|
|
|
The following example enhances the above simple union example by
|
2016-03-17 23:48:38 +01:00
|
|
|
adding an optional common member 'read-only', renaming the
|
|
|
|
discriminator to something more applicable than the simple union's
|
|
|
|
default of 'type', and reducing the number of {} required on the wire:
|
2013-07-03 15:58:57 +02:00
|
|
|
|
2015-09-03 10:18:06 +02:00
|
|
|
{ 'enum': 'BlockdevDriver', 'data': [ 'file', 'qcow2' ] }
|
2013-07-03 15:58:57 +02:00
|
|
|
{ 'union': 'BlockdevOptions',
|
2016-03-17 23:48:39 +01:00
|
|
|
'base': { 'driver': 'BlockdevDriver', '*read-only': 'bool' },
|
2013-07-03 15:58:57 +02:00
|
|
|
'discriminator': 'driver',
|
2016-03-17 23:48:38 +01:00
|
|
|
'data': { 'file': 'BlockdevOptionsFile',
|
|
|
|
'qcow2': 'BlockdevOptionsQcow2' } }
|
2013-07-03 15:58:57 +02:00
|
|
|
|
2015-05-04 17:04:59 +02:00
|
|
|
Resulting in these JSON objects:
|
|
|
|
|
2016-03-17 23:48:38 +01:00
|
|
|
{ "driver": "file", "read-only": true,
|
2015-05-04 17:04:59 +02:00
|
|
|
"filename": "/some/place/my-image" }
|
2016-03-17 23:48:38 +01:00
|
|
|
{ "driver": "qcow2", "read-only": false,
|
|
|
|
"backing": "/some/place/my-image", "lazy-refcounts": true }
|
2015-05-04 17:04:59 +02:00
|
|
|
|
|
|
|
Notice that in a flat union, the discriminator name is controlled by
|
|
|
|
the user, but because it must map to a base member with enum type, the
|
|
|
|
code generator can ensure that branches exist for all values of the
|
|
|
|
enum (although the order of the keys need not match the declaration of
|
|
|
|
the enum). In the resulting generated C data types, a flat union is
|
2016-03-03 17:16:46 +01:00
|
|
|
represented as a struct with the base members included directly, and
|
|
|
|
then a union of structures for each branch of the struct.
|
2015-05-04 17:04:59 +02:00
|
|
|
|
|
|
|
A simple union can always be re-written as a flat union where the base
|
|
|
|
class has a single member named 'type', and where each branch of the
|
2015-05-04 17:05:26 +02:00
|
|
|
union has a struct with a single member named 'data'. That is,
|
2013-07-03 15:58:57 +02:00
|
|
|
|
2015-05-04 17:04:59 +02:00
|
|
|
{ 'union': 'Simple', 'data': { 'one': 'str', 'two': 'int' } }
|
2013-07-03 15:58:57 +02:00
|
|
|
|
2015-05-04 17:04:59 +02:00
|
|
|
is identical on the wire to:
|
2013-07-03 15:58:57 +02:00
|
|
|
|
2015-05-04 17:04:59 +02:00
|
|
|
{ 'enum': 'Enum', 'data': ['one', 'two'] }
|
2015-05-04 17:05:26 +02:00
|
|
|
{ 'struct': 'Branch1', 'data': { 'data': 'str' } }
|
|
|
|
{ 'struct': 'Branch2', 'data': { 'data': 'int' } }
|
2016-03-17 23:48:39 +01:00
|
|
|
{ 'union': 'Flat': 'base': { 'type': 'Enum' }, 'discriminator': 'type',
|
2015-05-04 17:04:59 +02:00
|
|
|
'data': { 'one': 'Branch1', 'two': 'Branch2' } }
|
2013-07-08 16:14:21 +02:00
|
|
|
|
2015-05-04 17:04:59 +02:00
|
|
|
|
2015-05-04 17:05:12 +02:00
|
|
|
=== Alternate types ===
|
2013-07-08 16:14:21 +02:00
|
|
|
|
2015-05-04 17:05:12 +02:00
|
|
|
Usage: { 'alternate': STRING, 'data': DICT }
|
|
|
|
|
|
|
|
An alternate type is one that allows a choice between two or more JSON
|
|
|
|
data types (string, integer, number, or object, but currently not
|
|
|
|
array) on the wire. The definition is similar to a simple union type,
|
|
|
|
where each branch of the union names a QAPI type. For example:
|
|
|
|
|
2016-03-17 23:48:38 +01:00
|
|
|
{ 'alternate': 'BlockdevRef',
|
2013-07-08 16:14:21 +02:00
|
|
|
'data': { 'definition': 'BlockdevOptions',
|
|
|
|
'reference': 'str' } }
|
|
|
|
|
2015-05-04 17:05:12 +02:00
|
|
|
Unlike a union, the discriminator string is never passed on the wire
|
2015-05-04 17:05:35 +02:00
|
|
|
for the Client JSON Protocol. Instead, the value's JSON type serves
|
|
|
|
as an implicit discriminator, which in turn means that an alternate
|
|
|
|
can only express a choice between types represented differently in
|
|
|
|
JSON. If a branch is typed as the 'bool' built-in, the alternate
|
|
|
|
accepts true and false; if it is typed as any of the various numeric
|
|
|
|
built-ins, it accepts a JSON number; if it is typed as a 'str'
|
|
|
|
built-in or named enum type, it accepts a JSON string; and if it is
|
|
|
|
typed as a complex type (struct or union), it accepts a JSON object.
|
|
|
|
Two different complex types, for instance, aren't permitted, because
|
|
|
|
both are represented as a JSON object.
|
2015-05-04 17:05:12 +02:00
|
|
|
|
|
|
|
The example alternate declaration above allows using both of the
|
|
|
|
following example objects:
|
2013-07-08 16:14:21 +02:00
|
|
|
|
|
|
|
{ "file": "my_existing_block_device_id" }
|
|
|
|
{ "file": { "driver": "file",
|
2016-03-17 23:48:38 +01:00
|
|
|
"read-only": false,
|
2013-10-19 18:52:33 +02:00
|
|
|
"filename": "/tmp/mydisk.qcow2" } }
|
2013-07-08 16:14:21 +02:00
|
|
|
|
|
|
|
|
2013-07-16 13:17:27 +02:00
|
|
|
=== Commands ===
|
2011-07-19 21:50:46 +02:00
|
|
|
|
2015-05-04 17:04:59 +02:00
|
|
|
Usage: { 'command': STRING, '*data': COMPLEX-TYPE-NAME-OR-DICT,
|
qapi: Command returning anonymous type doesn't work, outlaw
Reproducer: with
{ 'command': 'user_def_cmd4', 'returns': { 'a': 'int' } }
added to qapi-schema-test.json, qapi-commands.py dies when it tries to
generate the command handler function
Traceback (most recent call last):
File "/work/armbru/qemu/scripts/qapi-commands.py", line 359, in <module>
ret = generate_command_decl(cmd['command'], arglist, ret_type) + "\n"
File "/work/armbru/qemu/scripts/qapi-commands.py", line 29, in generate_command_decl
ret_type=c_type(ret_type), name=c_name(name),
File "/work/armbru/qemu/scripts/qapi.py", line 927, in c_type
assert isinstance(value, str) and value != ""
AssertionError
because the return type doesn't exist.
Simply outlaw this usage, and drop or dumb down test cases accordingly.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
2015-07-31 17:59:38 +02:00
|
|
|
'*returns': TYPE-NAME,
|
2015-05-04 17:04:59 +02:00
|
|
|
'*gen': false, '*success-response': false }
|
|
|
|
|
|
|
|
Commands are defined by using a dictionary containing several members,
|
|
|
|
where three members are most common. The 'command' member is a
|
2015-05-04 17:05:35 +02:00
|
|
|
mandatory string, and determines the "execute" value passed in a
|
|
|
|
Client JSON Protocol command exchange.
|
2015-05-04 17:04:59 +02:00
|
|
|
|
|
|
|
The 'data' argument maps to the "arguments" dictionary passed in as
|
2015-05-04 17:05:35 +02:00
|
|
|
part of a Client JSON Protocol command. The 'data' member is optional
|
|
|
|
and defaults to {} (an empty dictionary). If present, it must be the
|
2015-07-01 10:12:24 +02:00
|
|
|
string name of a complex type, or a dictionary that declares an
|
|
|
|
anonymous type with the same semantics as a 'struct' expression, with
|
|
|
|
one exception noted below when 'gen' is used.
|
2015-05-04 17:04:59 +02:00
|
|
|
|
2016-03-03 17:16:46 +01:00
|
|
|
The 'returns' member describes what will appear in the "return" member
|
2015-05-04 17:05:35 +02:00
|
|
|
of a Client JSON Protocol reply on successful completion of a command.
|
|
|
|
The member is optional from the command declaration; if absent, the
|
2016-03-03 17:16:46 +01:00
|
|
|
"return" member will be an empty dictionary. If 'returns' is present,
|
2015-05-04 17:05:35 +02:00
|
|
|
it must be the string name of a complex or built-in type, a
|
|
|
|
one-element array containing the name of a complex or built-in type,
|
qapi: Command returning anonymous type doesn't work, outlaw
Reproducer: with
{ 'command': 'user_def_cmd4', 'returns': { 'a': 'int' } }
added to qapi-schema-test.json, qapi-commands.py dies when it tries to
generate the command handler function
Traceback (most recent call last):
File "/work/armbru/qemu/scripts/qapi-commands.py", line 359, in <module>
ret = generate_command_decl(cmd['command'], arglist, ret_type) + "\n"
File "/work/armbru/qemu/scripts/qapi-commands.py", line 29, in generate_command_decl
ret_type=c_type(ret_type), name=c_name(name),
File "/work/armbru/qemu/scripts/qapi.py", line 927, in c_type
assert isinstance(value, str) and value != ""
AssertionError
because the return type doesn't exist.
Simply outlaw this usage, and drop or dumb down test cases accordingly.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
2015-07-31 17:59:38 +02:00
|
|
|
with one exception noted below when 'gen' is used. Although it is
|
|
|
|
permitted to have the 'returns' member name a built-in type or an
|
|
|
|
array of built-in types, any command that does this cannot be extended
|
|
|
|
to return additional information in the future; thus, new commands
|
|
|
|
should strongly consider returning a dictionary-based type or an array
|
2016-03-03 17:16:46 +01:00
|
|
|
of dictionaries, even if the dictionary only contains one member at the
|
qapi: Command returning anonymous type doesn't work, outlaw
Reproducer: with
{ 'command': 'user_def_cmd4', 'returns': { 'a': 'int' } }
added to qapi-schema-test.json, qapi-commands.py dies when it tries to
generate the command handler function
Traceback (most recent call last):
File "/work/armbru/qemu/scripts/qapi-commands.py", line 359, in <module>
ret = generate_command_decl(cmd['command'], arglist, ret_type) + "\n"
File "/work/armbru/qemu/scripts/qapi-commands.py", line 29, in generate_command_decl
ret_type=c_type(ret_type), name=c_name(name),
File "/work/armbru/qemu/scripts/qapi.py", line 927, in c_type
assert isinstance(value, str) and value != ""
AssertionError
because the return type doesn't exist.
Simply outlaw this usage, and drop or dumb down test cases accordingly.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
2015-07-31 17:59:38 +02:00
|
|
|
present.
|
2015-05-04 17:05:35 +02:00
|
|
|
|
|
|
|
All commands in Client JSON Protocol use a dictionary to report
|
|
|
|
failure, with no way to specify that in QAPI. Where the error return
|
|
|
|
is different than the usual GenericError class in order to help the
|
|
|
|
client react differently to certain error conditions, it is worth
|
|
|
|
documenting this in the comments before the command declaration.
|
2015-05-04 17:04:59 +02:00
|
|
|
|
|
|
|
Some example commands:
|
|
|
|
|
|
|
|
{ 'command': 'my-first-command',
|
|
|
|
'data': { 'arg1': 'str', '*arg2': 'str' } }
|
2015-05-04 17:05:26 +02:00
|
|
|
{ 'struct': 'MyType', 'data': { '*value': 'str' } }
|
2015-05-04 17:04:59 +02:00
|
|
|
{ 'command': 'my-second-command',
|
|
|
|
'returns': [ 'MyType' ] }
|
|
|
|
|
2015-05-04 17:05:35 +02:00
|
|
|
which would validate this Client JSON Protocol transaction:
|
2015-05-04 17:04:59 +02:00
|
|
|
|
|
|
|
=> { "execute": "my-first-command",
|
|
|
|
"arguments": { "arg1": "hello" } }
|
|
|
|
<= { "return": { } }
|
|
|
|
=> { "execute": "my-second-command" }
|
|
|
|
<= { "return": [ { "value": "one" }, { } ] }
|
|
|
|
|
|
|
|
In rare cases, QAPI cannot express a type-safe representation of a
|
2015-09-16 13:06:27 +02:00
|
|
|
corresponding Client JSON Protocol command. You then have to suppress
|
|
|
|
generation of a marshalling function by including a key 'gen' with
|
|
|
|
boolean value false, and instead write your own function. Please try
|
|
|
|
to avoid adding new commands that rely on this, and instead use
|
|
|
|
type-safe unions. For an example of this usage:
|
2015-05-04 17:04:59 +02:00
|
|
|
|
|
|
|
{ 'command': 'netdev_add',
|
2015-09-16 13:06:26 +02:00
|
|
|
'data': {'type': 'str', 'id': 'str'},
|
2015-05-04 17:04:59 +02:00
|
|
|
'gen': false }
|
|
|
|
|
|
|
|
Normally, the QAPI schema is used to describe synchronous exchanges,
|
|
|
|
where a response is expected. But in some cases, the action of a
|
|
|
|
command is expected to change state in a way that a successful
|
|
|
|
response is not possible (although the command will still return a
|
|
|
|
normal dictionary error on failure). When a successful reply is not
|
|
|
|
possible, the command expression should include the optional key
|
|
|
|
'success-response' with boolean value false. So far, only QGA makes
|
2016-03-03 17:16:46 +01:00
|
|
|
use of this member.
|
2011-07-19 21:50:46 +02:00
|
|
|
|
|
|
|
|
2014-06-18 08:43:28 +02:00
|
|
|
=== Events ===
|
|
|
|
|
2015-05-04 17:04:59 +02:00
|
|
|
Usage: { 'event': STRING, '*data': COMPLEX-TYPE-NAME-OR-DICT }
|
|
|
|
|
|
|
|
Events are defined with the keyword 'event'. It is not allowed to
|
|
|
|
name an event 'MAX', since the generator also produces a C enumeration
|
|
|
|
of all event names with a generated _MAX value at the end. When
|
|
|
|
'data' is also specified, additional info will be included in the
|
2015-05-04 17:05:26 +02:00
|
|
|
event, with similar semantics to a 'struct' expression. Finally there
|
2015-05-04 17:04:59 +02:00
|
|
|
will be C API generated in qapi-event.h; when called by QEMU code, a
|
|
|
|
message with timestamp will be emitted on the wire.
|
2014-06-18 08:43:28 +02:00
|
|
|
|
|
|
|
An example event is:
|
|
|
|
|
|
|
|
{ 'event': 'EVENT_C',
|
|
|
|
'data': { '*a': 'int', 'b': 'str' } }
|
|
|
|
|
|
|
|
Resulting in this JSON object:
|
|
|
|
|
|
|
|
{ "event": "EVENT_C",
|
|
|
|
"data": { "b": "test string" },
|
|
|
|
"timestamp": { "seconds": 1267020223, "microseconds": 435656 } }
|
2011-07-19 21:50:46 +02:00
|
|
|
|
2014-09-26 17:20:33 +02:00
|
|
|
|
qapi: New QMP command query-qmp-schema for QMP introspection
qapi/introspect.json defines the introspection schema. It's designed
for QMP introspection, but should do for similar uses, such as QGA.
The introspection schema does not reflect all the rules and
restrictions that apply to QAPI schemata. A valid QAPI schema has an
introspection value conforming to the introspection schema, but the
converse is not true.
Introspection lowers away a number of schema details, and makes
implicit things explicit:
* The built-in types are declared with their JSON type.
All integer types are mapped to 'int', because how many bits we use
internally is an implementation detail. It could be pressed into
external interface service as very approximate range information,
but that's a bad idea. If we need range information, we better do
it properly.
* Implicit type definitions are made explicit, and given
auto-generated names:
- Array types, named by appending "List" to the name of their
element type, like in generated C.
- The enumeration types implicitly defined by simple union types,
named by appending "Kind" to the name of their simple union type,
like in generated C.
- Types that don't occur in generated C. Their names start with ':'
so they don't clash with the user's names.
* All type references are by name.
* The struct and union types are generalized into an object type.
* Base types are flattened.
* Commands take a single argument and return a single result.
Dictionary argument or list result is an implicit type definition.
The empty object type is used when a command takes no arguments or
produces no results.
The argument is always of object type, but the introspection schema
doesn't reflect that.
The 'gen': false directive is omitted as implementation detail.
The 'success-response' directive is omitted as well for now, even
though it's not an implementation detail, because it's not used by
QMP.
* Events carry a single data value.
Implicit type definition and empty object type use, just like for
commands.
The value is of object type, but the introspection schema doesn't
reflect that.
* Types not used by commands or events are omitted.
Indirect use counts as use.
* Optional members have a default, which can only be null right now
Instead of a mandatory "optional" flag, we have an optional default.
No default means mandatory, default null means optional without
default value. Non-null is available for optional with default
(possible future extension).
* Clients should *not* look up types by name, because type names are
not ABI. Look up the command or event you're interested in, then
follow the references.
TODO Should we hide the type names to eliminate the temptation?
New generator scripts/qapi-introspect.py computes an introspection
value for its input, and generates a C variable holding it.
It can generate awfully long lines. Marked TODO.
A new test-qmp-input-visitor test case feeds its result for both
tests/qapi-schema/qapi-schema-test.json and qapi-schema.json to a
QmpInputVisitor to verify it actually conforms to the schema.
New QMP command query-qmp-schema takes its return value from that
variable. Its reply is some 85KiBytes for me right now.
If this turns out to be too much, we have a couple of options:
* We can use shorter names in the JSON. Not the QMP style.
* Optionally return the sub-schema for commands and events given as
arguments.
Right now qmp_query_schema() sends the string literal computed by
qmp-introspect.py. To compute sub-schema at run time, we'd have to
duplicate parts of qapi-introspect.py in C. Unattractive.
* Let clients cache the output of query-qmp-schema.
It changes only on QEMU upgrades, i.e. rarely. Provide a command
query-qmp-schema-hash. Clients can have a cache indexed by hash,
and re-query the schema only when they don't have it cached. Even
simpler: put the hash in the QMP greeting.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
2015-09-16 13:06:28 +02:00
|
|
|
== Client JSON Protocol introspection ==
|
|
|
|
|
|
|
|
Clients of a Client JSON Protocol commonly need to figure out what
|
|
|
|
exactly the server (QEMU) supports.
|
|
|
|
|
|
|
|
For this purpose, QMP provides introspection via command
|
|
|
|
query-qmp-schema. QGA currently doesn't support introspection.
|
|
|
|
|
2015-11-11 18:50:02 +01:00
|
|
|
While Client JSON Protocol wire compatibility should be maintained
|
|
|
|
between qemu versions, we cannot make the same guarantees for
|
|
|
|
introspection stability. For example, one version of qemu may provide
|
|
|
|
a non-variant optional member of a struct, and a later version rework
|
|
|
|
the member to instead be non-optional and associated with a variant.
|
|
|
|
Likewise, one version of qemu may list a member with open-ended type
|
|
|
|
'str', and a later version could convert it to a finite set of strings
|
|
|
|
via an enum type; or a member may be converted from a specific type to
|
|
|
|
an alternate that represents a choice between the original type and
|
|
|
|
something else.
|
|
|
|
|
qapi: New QMP command query-qmp-schema for QMP introspection
qapi/introspect.json defines the introspection schema. It's designed
for QMP introspection, but should do for similar uses, such as QGA.
The introspection schema does not reflect all the rules and
restrictions that apply to QAPI schemata. A valid QAPI schema has an
introspection value conforming to the introspection schema, but the
converse is not true.
Introspection lowers away a number of schema details, and makes
implicit things explicit:
* The built-in types are declared with their JSON type.
All integer types are mapped to 'int', because how many bits we use
internally is an implementation detail. It could be pressed into
external interface service as very approximate range information,
but that's a bad idea. If we need range information, we better do
it properly.
* Implicit type definitions are made explicit, and given
auto-generated names:
- Array types, named by appending "List" to the name of their
element type, like in generated C.
- The enumeration types implicitly defined by simple union types,
named by appending "Kind" to the name of their simple union type,
like in generated C.
- Types that don't occur in generated C. Their names start with ':'
so they don't clash with the user's names.
* All type references are by name.
* The struct and union types are generalized into an object type.
* Base types are flattened.
* Commands take a single argument and return a single result.
Dictionary argument or list result is an implicit type definition.
The empty object type is used when a command takes no arguments or
produces no results.
The argument is always of object type, but the introspection schema
doesn't reflect that.
The 'gen': false directive is omitted as implementation detail.
The 'success-response' directive is omitted as well for now, even
though it's not an implementation detail, because it's not used by
QMP.
* Events carry a single data value.
Implicit type definition and empty object type use, just like for
commands.
The value is of object type, but the introspection schema doesn't
reflect that.
* Types not used by commands or events are omitted.
Indirect use counts as use.
* Optional members have a default, which can only be null right now
Instead of a mandatory "optional" flag, we have an optional default.
No default means mandatory, default null means optional without
default value. Non-null is available for optional with default
(possible future extension).
* Clients should *not* look up types by name, because type names are
not ABI. Look up the command or event you're interested in, then
follow the references.
TODO Should we hide the type names to eliminate the temptation?
New generator scripts/qapi-introspect.py computes an introspection
value for its input, and generates a C variable holding it.
It can generate awfully long lines. Marked TODO.
A new test-qmp-input-visitor test case feeds its result for both
tests/qapi-schema/qapi-schema-test.json and qapi-schema.json to a
QmpInputVisitor to verify it actually conforms to the schema.
New QMP command query-qmp-schema takes its return value from that
variable. Its reply is some 85KiBytes for me right now.
If this turns out to be too much, we have a couple of options:
* We can use shorter names in the JSON. Not the QMP style.
* Optionally return the sub-schema for commands and events given as
arguments.
Right now qmp_query_schema() sends the string literal computed by
qmp-introspect.py. To compute sub-schema at run time, we'd have to
duplicate parts of qapi-introspect.py in C. Unattractive.
* Let clients cache the output of query-qmp-schema.
It changes only on QEMU upgrades, i.e. rarely. Provide a command
query-qmp-schema-hash. Clients can have a cache indexed by hash,
and re-query the schema only when they don't have it cached. Even
simpler: put the hash in the QMP greeting.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
2015-09-16 13:06:28 +02:00
|
|
|
query-qmp-schema returns a JSON array of SchemaInfo objects. These
|
|
|
|
objects together describe the wire ABI, as defined in the QAPI schema.
|
qapi-introspect: Document lack of sorting
qapi-code-gen.txt already claims that types, commands, and
events share a common namespace; set this in stone by further
documenting that our introspection output will never have
collisions with the same name tied to more than one meta-type.
Our largest QMP enum currently has 125 values, our largest
object type has 27 members, and the mean for each is less than
10. These sizes are small enough that the per-element overhead
of O(log n) binary searching probably outweighs the speed
possible with direct O(n) linear searching (a better algorithm
with more overhead will only beat a leaner naive algorithm only
as you scale to larger input sizes).
Arguably, the overall SchemaInfo array could be sorted by name;
there, we currently have 531 entities, large enough for a binary
search to be faster than linear. However, remember that we have
mutually-recursive types, which means there is no topological
ordering that will allow clients to learn all information about
that type in a single linear pass; thus clients will want to do
random access over the data, and they will probably read the
introspection output into a hashtable for O(1) lookup rather
than O(log n) binary searching, at which point, pre-sorting our
introspection output doesn't help the client.
It doesn't help that sorting can be subjective if you introduce
locales into the mix (I'm not experienced enough with Python
to know for sure, but at least it looks like it defaults to
sorting in the C locale even when run under a different locale).
And while our current introspection output is deterministic
(because we visit entities in a sorted order), we may want
to change that order in the future (such as using OrderedDict
to stick to .json declaration order).
For these reasons, we simply document that clients should not
rely on any particular order of items in introspection output.
And since it is now a documented part of the contract, we have
the freedom to later rearrange output if needed, without
worrying about breaking well-written clients.
Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1446791754-23823-13-git-send-email-eblake@redhat.com>
[Commit message tweaked]
Signed-off-by: Markus Armbruster <armbru@redhat.com>
2015-11-06 07:35:36 +01:00
|
|
|
There is no specified order to the SchemaInfo objects returned; a
|
|
|
|
client must search for a particular name throughout the entire array
|
|
|
|
to learn more about that name, but is at least guaranteed that there
|
|
|
|
will be no collisions between type, command, and event names.
|
qapi: New QMP command query-qmp-schema for QMP introspection
qapi/introspect.json defines the introspection schema. It's designed
for QMP introspection, but should do for similar uses, such as QGA.
The introspection schema does not reflect all the rules and
restrictions that apply to QAPI schemata. A valid QAPI schema has an
introspection value conforming to the introspection schema, but the
converse is not true.
Introspection lowers away a number of schema details, and makes
implicit things explicit:
* The built-in types are declared with their JSON type.
All integer types are mapped to 'int', because how many bits we use
internally is an implementation detail. It could be pressed into
external interface service as very approximate range information,
but that's a bad idea. If we need range information, we better do
it properly.
* Implicit type definitions are made explicit, and given
auto-generated names:
- Array types, named by appending "List" to the name of their
element type, like in generated C.
- The enumeration types implicitly defined by simple union types,
named by appending "Kind" to the name of their simple union type,
like in generated C.
- Types that don't occur in generated C. Their names start with ':'
so they don't clash with the user's names.
* All type references are by name.
* The struct and union types are generalized into an object type.
* Base types are flattened.
* Commands take a single argument and return a single result.
Dictionary argument or list result is an implicit type definition.
The empty object type is used when a command takes no arguments or
produces no results.
The argument is always of object type, but the introspection schema
doesn't reflect that.
The 'gen': false directive is omitted as implementation detail.
The 'success-response' directive is omitted as well for now, even
though it's not an implementation detail, because it's not used by
QMP.
* Events carry a single data value.
Implicit type definition and empty object type use, just like for
commands.
The value is of object type, but the introspection schema doesn't
reflect that.
* Types not used by commands or events are omitted.
Indirect use counts as use.
* Optional members have a default, which can only be null right now
Instead of a mandatory "optional" flag, we have an optional default.
No default means mandatory, default null means optional without
default value. Non-null is available for optional with default
(possible future extension).
* Clients should *not* look up types by name, because type names are
not ABI. Look up the command or event you're interested in, then
follow the references.
TODO Should we hide the type names to eliminate the temptation?
New generator scripts/qapi-introspect.py computes an introspection
value for its input, and generates a C variable holding it.
It can generate awfully long lines. Marked TODO.
A new test-qmp-input-visitor test case feeds its result for both
tests/qapi-schema/qapi-schema-test.json and qapi-schema.json to a
QmpInputVisitor to verify it actually conforms to the schema.
New QMP command query-qmp-schema takes its return value from that
variable. Its reply is some 85KiBytes for me right now.
If this turns out to be too much, we have a couple of options:
* We can use shorter names in the JSON. Not the QMP style.
* Optionally return the sub-schema for commands and events given as
arguments.
Right now qmp_query_schema() sends the string literal computed by
qmp-introspect.py. To compute sub-schema at run time, we'd have to
duplicate parts of qapi-introspect.py in C. Unattractive.
* Let clients cache the output of query-qmp-schema.
It changes only on QEMU upgrades, i.e. rarely. Provide a command
query-qmp-schema-hash. Clients can have a cache indexed by hash,
and re-query the schema only when they don't have it cached. Even
simpler: put the hash in the QMP greeting.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
2015-09-16 13:06:28 +02:00
|
|
|
|
|
|
|
However, the SchemaInfo can't reflect all the rules and restrictions
|
|
|
|
that apply to QMP. It's interface introspection (figuring out what's
|
|
|
|
there), not interface specification. The specification is in the QAPI
|
|
|
|
schema. To understand how QMP is to be used, you need to study the
|
|
|
|
QAPI schema.
|
|
|
|
|
|
|
|
Like any other command, query-qmp-schema is itself defined in the QAPI
|
|
|
|
schema, along with the SchemaInfo type. This text attempts to give an
|
|
|
|
overview how things work. For details you need to consult the QAPI
|
|
|
|
schema.
|
|
|
|
|
|
|
|
SchemaInfo objects have common members "name" and "meta-type", and
|
|
|
|
additional variant members depending on the value of meta-type.
|
|
|
|
|
|
|
|
Each SchemaInfo object describes a wire ABI entity of a certain
|
|
|
|
meta-type: a command, event or one of several kinds of type.
|
|
|
|
|
2015-09-16 13:06:29 +02:00
|
|
|
SchemaInfo for commands and events have the same name as in the QAPI
|
|
|
|
schema.
|
qapi: New QMP command query-qmp-schema for QMP introspection
qapi/introspect.json defines the introspection schema. It's designed
for QMP introspection, but should do for similar uses, such as QGA.
The introspection schema does not reflect all the rules and
restrictions that apply to QAPI schemata. A valid QAPI schema has an
introspection value conforming to the introspection schema, but the
converse is not true.
Introspection lowers away a number of schema details, and makes
implicit things explicit:
* The built-in types are declared with their JSON type.
All integer types are mapped to 'int', because how many bits we use
internally is an implementation detail. It could be pressed into
external interface service as very approximate range information,
but that's a bad idea. If we need range information, we better do
it properly.
* Implicit type definitions are made explicit, and given
auto-generated names:
- Array types, named by appending "List" to the name of their
element type, like in generated C.
- The enumeration types implicitly defined by simple union types,
named by appending "Kind" to the name of their simple union type,
like in generated C.
- Types that don't occur in generated C. Their names start with ':'
so they don't clash with the user's names.
* All type references are by name.
* The struct and union types are generalized into an object type.
* Base types are flattened.
* Commands take a single argument and return a single result.
Dictionary argument or list result is an implicit type definition.
The empty object type is used when a command takes no arguments or
produces no results.
The argument is always of object type, but the introspection schema
doesn't reflect that.
The 'gen': false directive is omitted as implementation detail.
The 'success-response' directive is omitted as well for now, even
though it's not an implementation detail, because it's not used by
QMP.
* Events carry a single data value.
Implicit type definition and empty object type use, just like for
commands.
The value is of object type, but the introspection schema doesn't
reflect that.
* Types not used by commands or events are omitted.
Indirect use counts as use.
* Optional members have a default, which can only be null right now
Instead of a mandatory "optional" flag, we have an optional default.
No default means mandatory, default null means optional without
default value. Non-null is available for optional with default
(possible future extension).
* Clients should *not* look up types by name, because type names are
not ABI. Look up the command or event you're interested in, then
follow the references.
TODO Should we hide the type names to eliminate the temptation?
New generator scripts/qapi-introspect.py computes an introspection
value for its input, and generates a C variable holding it.
It can generate awfully long lines. Marked TODO.
A new test-qmp-input-visitor test case feeds its result for both
tests/qapi-schema/qapi-schema-test.json and qapi-schema.json to a
QmpInputVisitor to verify it actually conforms to the schema.
New QMP command query-qmp-schema takes its return value from that
variable. Its reply is some 85KiBytes for me right now.
If this turns out to be too much, we have a couple of options:
* We can use shorter names in the JSON. Not the QMP style.
* Optionally return the sub-schema for commands and events given as
arguments.
Right now qmp_query_schema() sends the string literal computed by
qmp-introspect.py. To compute sub-schema at run time, we'd have to
duplicate parts of qapi-introspect.py in C. Unattractive.
* Let clients cache the output of query-qmp-schema.
It changes only on QEMU upgrades, i.e. rarely. Provide a command
query-qmp-schema-hash. Clients can have a cache indexed by hash,
and re-query the schema only when they don't have it cached. Even
simpler: put the hash in the QMP greeting.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
2015-09-16 13:06:28 +02:00
|
|
|
|
|
|
|
Command and event names are part of the wire ABI, but type names are
|
2015-09-16 13:06:29 +02:00
|
|
|
not. Therefore, the SchemaInfo for types have auto-generated
|
|
|
|
meaningless names. For readability, the examples in this section use
|
|
|
|
meaningful type names instead.
|
|
|
|
|
|
|
|
To examine a type, start with a command or event using it, then follow
|
|
|
|
references by name.
|
qapi: New QMP command query-qmp-schema for QMP introspection
qapi/introspect.json defines the introspection schema. It's designed
for QMP introspection, but should do for similar uses, such as QGA.
The introspection schema does not reflect all the rules and
restrictions that apply to QAPI schemata. A valid QAPI schema has an
introspection value conforming to the introspection schema, but the
converse is not true.
Introspection lowers away a number of schema details, and makes
implicit things explicit:
* The built-in types are declared with their JSON type.
All integer types are mapped to 'int', because how many bits we use
internally is an implementation detail. It could be pressed into
external interface service as very approximate range information,
but that's a bad idea. If we need range information, we better do
it properly.
* Implicit type definitions are made explicit, and given
auto-generated names:
- Array types, named by appending "List" to the name of their
element type, like in generated C.
- The enumeration types implicitly defined by simple union types,
named by appending "Kind" to the name of their simple union type,
like in generated C.
- Types that don't occur in generated C. Their names start with ':'
so they don't clash with the user's names.
* All type references are by name.
* The struct and union types are generalized into an object type.
* Base types are flattened.
* Commands take a single argument and return a single result.
Dictionary argument or list result is an implicit type definition.
The empty object type is used when a command takes no arguments or
produces no results.
The argument is always of object type, but the introspection schema
doesn't reflect that.
The 'gen': false directive is omitted as implementation detail.
The 'success-response' directive is omitted as well for now, even
though it's not an implementation detail, because it's not used by
QMP.
* Events carry a single data value.
Implicit type definition and empty object type use, just like for
commands.
The value is of object type, but the introspection schema doesn't
reflect that.
* Types not used by commands or events are omitted.
Indirect use counts as use.
* Optional members have a default, which can only be null right now
Instead of a mandatory "optional" flag, we have an optional default.
No default means mandatory, default null means optional without
default value. Non-null is available for optional with default
(possible future extension).
* Clients should *not* look up types by name, because type names are
not ABI. Look up the command or event you're interested in, then
follow the references.
TODO Should we hide the type names to eliminate the temptation?
New generator scripts/qapi-introspect.py computes an introspection
value for its input, and generates a C variable holding it.
It can generate awfully long lines. Marked TODO.
A new test-qmp-input-visitor test case feeds its result for both
tests/qapi-schema/qapi-schema-test.json and qapi-schema.json to a
QmpInputVisitor to verify it actually conforms to the schema.
New QMP command query-qmp-schema takes its return value from that
variable. Its reply is some 85KiBytes for me right now.
If this turns out to be too much, we have a couple of options:
* We can use shorter names in the JSON. Not the QMP style.
* Optionally return the sub-schema for commands and events given as
arguments.
Right now qmp_query_schema() sends the string literal computed by
qmp-introspect.py. To compute sub-schema at run time, we'd have to
duplicate parts of qapi-introspect.py in C. Unattractive.
* Let clients cache the output of query-qmp-schema.
It changes only on QEMU upgrades, i.e. rarely. Provide a command
query-qmp-schema-hash. Clients can have a cache indexed by hash,
and re-query the schema only when they don't have it cached. Even
simpler: put the hash in the QMP greeting.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
2015-09-16 13:06:28 +02:00
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QAPI schema definitions not reachable that way are omitted.
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The SchemaInfo for a command has meta-type "command", and variant
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members "arg-type" and "ret-type". On the wire, the "arguments"
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member of a client's "execute" command must conform to the object type
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named by "arg-type". The "return" member that the server passes in a
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success response conforms to the type named by "ret-type".
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If the command takes no arguments, "arg-type" names an object type
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without members. Likewise, if the command returns nothing, "ret-type"
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names an object type without members.
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Example: the SchemaInfo for command query-qmp-schema
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{ "name": "query-qmp-schema", "meta-type": "command",
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2016-03-17 23:48:29 +01:00
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"arg-type": "q_empty", "ret-type": "SchemaInfoList" }
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qapi: New QMP command query-qmp-schema for QMP introspection
qapi/introspect.json defines the introspection schema. It's designed
for QMP introspection, but should do for similar uses, such as QGA.
The introspection schema does not reflect all the rules and
restrictions that apply to QAPI schemata. A valid QAPI schema has an
introspection value conforming to the introspection schema, but the
converse is not true.
Introspection lowers away a number of schema details, and makes
implicit things explicit:
* The built-in types are declared with their JSON type.
All integer types are mapped to 'int', because how many bits we use
internally is an implementation detail. It could be pressed into
external interface service as very approximate range information,
but that's a bad idea. If we need range information, we better do
it properly.
* Implicit type definitions are made explicit, and given
auto-generated names:
- Array types, named by appending "List" to the name of their
element type, like in generated C.
- The enumeration types implicitly defined by simple union types,
named by appending "Kind" to the name of their simple union type,
like in generated C.
- Types that don't occur in generated C. Their names start with ':'
so they don't clash with the user's names.
* All type references are by name.
* The struct and union types are generalized into an object type.
* Base types are flattened.
* Commands take a single argument and return a single result.
Dictionary argument or list result is an implicit type definition.
The empty object type is used when a command takes no arguments or
produces no results.
The argument is always of object type, but the introspection schema
doesn't reflect that.
The 'gen': false directive is omitted as implementation detail.
The 'success-response' directive is omitted as well for now, even
though it's not an implementation detail, because it's not used by
QMP.
* Events carry a single data value.
Implicit type definition and empty object type use, just like for
commands.
The value is of object type, but the introspection schema doesn't
reflect that.
* Types not used by commands or events are omitted.
Indirect use counts as use.
* Optional members have a default, which can only be null right now
Instead of a mandatory "optional" flag, we have an optional default.
No default means mandatory, default null means optional without
default value. Non-null is available for optional with default
(possible future extension).
* Clients should *not* look up types by name, because type names are
not ABI. Look up the command or event you're interested in, then
follow the references.
TODO Should we hide the type names to eliminate the temptation?
New generator scripts/qapi-introspect.py computes an introspection
value for its input, and generates a C variable holding it.
It can generate awfully long lines. Marked TODO.
A new test-qmp-input-visitor test case feeds its result for both
tests/qapi-schema/qapi-schema-test.json and qapi-schema.json to a
QmpInputVisitor to verify it actually conforms to the schema.
New QMP command query-qmp-schema takes its return value from that
variable. Its reply is some 85KiBytes for me right now.
If this turns out to be too much, we have a couple of options:
* We can use shorter names in the JSON. Not the QMP style.
* Optionally return the sub-schema for commands and events given as
arguments.
Right now qmp_query_schema() sends the string literal computed by
qmp-introspect.py. To compute sub-schema at run time, we'd have to
duplicate parts of qapi-introspect.py in C. Unattractive.
* Let clients cache the output of query-qmp-schema.
It changes only on QEMU upgrades, i.e. rarely. Provide a command
query-qmp-schema-hash. Clients can have a cache indexed by hash,
and re-query the schema only when they don't have it cached. Even
simpler: put the hash in the QMP greeting.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
2015-09-16 13:06:28 +02:00
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2016-03-17 23:48:29 +01:00
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Type "q_empty" is an automatic object type without members, and type
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qapi: New QMP command query-qmp-schema for QMP introspection
qapi/introspect.json defines the introspection schema. It's designed
for QMP introspection, but should do for similar uses, such as QGA.
The introspection schema does not reflect all the rules and
restrictions that apply to QAPI schemata. A valid QAPI schema has an
introspection value conforming to the introspection schema, but the
converse is not true.
Introspection lowers away a number of schema details, and makes
implicit things explicit:
* The built-in types are declared with their JSON type.
All integer types are mapped to 'int', because how many bits we use
internally is an implementation detail. It could be pressed into
external interface service as very approximate range information,
but that's a bad idea. If we need range information, we better do
it properly.
* Implicit type definitions are made explicit, and given
auto-generated names:
- Array types, named by appending "List" to the name of their
element type, like in generated C.
- The enumeration types implicitly defined by simple union types,
named by appending "Kind" to the name of their simple union type,
like in generated C.
- Types that don't occur in generated C. Their names start with ':'
so they don't clash with the user's names.
* All type references are by name.
* The struct and union types are generalized into an object type.
* Base types are flattened.
* Commands take a single argument and return a single result.
Dictionary argument or list result is an implicit type definition.
The empty object type is used when a command takes no arguments or
produces no results.
The argument is always of object type, but the introspection schema
doesn't reflect that.
The 'gen': false directive is omitted as implementation detail.
The 'success-response' directive is omitted as well for now, even
though it's not an implementation detail, because it's not used by
QMP.
* Events carry a single data value.
Implicit type definition and empty object type use, just like for
commands.
The value is of object type, but the introspection schema doesn't
reflect that.
* Types not used by commands or events are omitted.
Indirect use counts as use.
* Optional members have a default, which can only be null right now
Instead of a mandatory "optional" flag, we have an optional default.
No default means mandatory, default null means optional without
default value. Non-null is available for optional with default
(possible future extension).
* Clients should *not* look up types by name, because type names are
not ABI. Look up the command or event you're interested in, then
follow the references.
TODO Should we hide the type names to eliminate the temptation?
New generator scripts/qapi-introspect.py computes an introspection
value for its input, and generates a C variable holding it.
It can generate awfully long lines. Marked TODO.
A new test-qmp-input-visitor test case feeds its result for both
tests/qapi-schema/qapi-schema-test.json and qapi-schema.json to a
QmpInputVisitor to verify it actually conforms to the schema.
New QMP command query-qmp-schema takes its return value from that
variable. Its reply is some 85KiBytes for me right now.
If this turns out to be too much, we have a couple of options:
* We can use shorter names in the JSON. Not the QMP style.
* Optionally return the sub-schema for commands and events given as
arguments.
Right now qmp_query_schema() sends the string literal computed by
qmp-introspect.py. To compute sub-schema at run time, we'd have to
duplicate parts of qapi-introspect.py in C. Unattractive.
* Let clients cache the output of query-qmp-schema.
It changes only on QEMU upgrades, i.e. rarely. Provide a command
query-qmp-schema-hash. Clients can have a cache indexed by hash,
and re-query the schema only when they don't have it cached. Even
simpler: put the hash in the QMP greeting.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
2015-09-16 13:06:28 +02:00
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"SchemaInfoList" is the array of SchemaInfo type.
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The SchemaInfo for an event has meta-type "event", and variant member
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"arg-type". On the wire, a "data" member that the server passes in an
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event conforms to the object type named by "arg-type".
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If the event carries no additional information, "arg-type" names an
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object type without members. The event may not have a data member on
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the wire then.
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Each command or event defined with dictionary-valued 'data' in the
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2015-09-16 13:06:29 +02:00
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QAPI schema implicitly defines an object type.
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qapi: New QMP command query-qmp-schema for QMP introspection
qapi/introspect.json defines the introspection schema. It's designed
for QMP introspection, but should do for similar uses, such as QGA.
The introspection schema does not reflect all the rules and
restrictions that apply to QAPI schemata. A valid QAPI schema has an
introspection value conforming to the introspection schema, but the
converse is not true.
Introspection lowers away a number of schema details, and makes
implicit things explicit:
* The built-in types are declared with their JSON type.
All integer types are mapped to 'int', because how many bits we use
internally is an implementation detail. It could be pressed into
external interface service as very approximate range information,
but that's a bad idea. If we need range information, we better do
it properly.
* Implicit type definitions are made explicit, and given
auto-generated names:
- Array types, named by appending "List" to the name of their
element type, like in generated C.
- The enumeration types implicitly defined by simple union types,
named by appending "Kind" to the name of their simple union type,
like in generated C.
- Types that don't occur in generated C. Their names start with ':'
so they don't clash with the user's names.
* All type references are by name.
* The struct and union types are generalized into an object type.
* Base types are flattened.
* Commands take a single argument and return a single result.
Dictionary argument or list result is an implicit type definition.
The empty object type is used when a command takes no arguments or
produces no results.
The argument is always of object type, but the introspection schema
doesn't reflect that.
The 'gen': false directive is omitted as implementation detail.
The 'success-response' directive is omitted as well for now, even
though it's not an implementation detail, because it's not used by
QMP.
* Events carry a single data value.
Implicit type definition and empty object type use, just like for
commands.
The value is of object type, but the introspection schema doesn't
reflect that.
* Types not used by commands or events are omitted.
Indirect use counts as use.
* Optional members have a default, which can only be null right now
Instead of a mandatory "optional" flag, we have an optional default.
No default means mandatory, default null means optional without
default value. Non-null is available for optional with default
(possible future extension).
* Clients should *not* look up types by name, because type names are
not ABI. Look up the command or event you're interested in, then
follow the references.
TODO Should we hide the type names to eliminate the temptation?
New generator scripts/qapi-introspect.py computes an introspection
value for its input, and generates a C variable holding it.
It can generate awfully long lines. Marked TODO.
A new test-qmp-input-visitor test case feeds its result for both
tests/qapi-schema/qapi-schema-test.json and qapi-schema.json to a
QmpInputVisitor to verify it actually conforms to the schema.
New QMP command query-qmp-schema takes its return value from that
variable. Its reply is some 85KiBytes for me right now.
If this turns out to be too much, we have a couple of options:
* We can use shorter names in the JSON. Not the QMP style.
* Optionally return the sub-schema for commands and events given as
arguments.
Right now qmp_query_schema() sends the string literal computed by
qmp-introspect.py. To compute sub-schema at run time, we'd have to
duplicate parts of qapi-introspect.py in C. Unattractive.
* Let clients cache the output of query-qmp-schema.
It changes only on QEMU upgrades, i.e. rarely. Provide a command
query-qmp-schema-hash. Clients can have a cache indexed by hash,
and re-query the schema only when they don't have it cached. Even
simpler: put the hash in the QMP greeting.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
2015-09-16 13:06:28 +02:00
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Example: the SchemaInfo for EVENT_C from section Events
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{ "name": "EVENT_C", "meta-type": "event",
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2016-03-17 23:48:29 +01:00
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"arg-type": "q_obj-EVENT_C-arg" }
|
qapi: New QMP command query-qmp-schema for QMP introspection
qapi/introspect.json defines the introspection schema. It's designed
for QMP introspection, but should do for similar uses, such as QGA.
The introspection schema does not reflect all the rules and
restrictions that apply to QAPI schemata. A valid QAPI schema has an
introspection value conforming to the introspection schema, but the
converse is not true.
Introspection lowers away a number of schema details, and makes
implicit things explicit:
* The built-in types are declared with their JSON type.
All integer types are mapped to 'int', because how many bits we use
internally is an implementation detail. It could be pressed into
external interface service as very approximate range information,
but that's a bad idea. If we need range information, we better do
it properly.
* Implicit type definitions are made explicit, and given
auto-generated names:
- Array types, named by appending "List" to the name of their
element type, like in generated C.
- The enumeration types implicitly defined by simple union types,
named by appending "Kind" to the name of their simple union type,
like in generated C.
- Types that don't occur in generated C. Their names start with ':'
so they don't clash with the user's names.
* All type references are by name.
* The struct and union types are generalized into an object type.
* Base types are flattened.
* Commands take a single argument and return a single result.
Dictionary argument or list result is an implicit type definition.
The empty object type is used when a command takes no arguments or
produces no results.
The argument is always of object type, but the introspection schema
doesn't reflect that.
The 'gen': false directive is omitted as implementation detail.
The 'success-response' directive is omitted as well for now, even
though it's not an implementation detail, because it's not used by
QMP.
* Events carry a single data value.
Implicit type definition and empty object type use, just like for
commands.
The value is of object type, but the introspection schema doesn't
reflect that.
* Types not used by commands or events are omitted.
Indirect use counts as use.
* Optional members have a default, which can only be null right now
Instead of a mandatory "optional" flag, we have an optional default.
No default means mandatory, default null means optional without
default value. Non-null is available for optional with default
(possible future extension).
* Clients should *not* look up types by name, because type names are
not ABI. Look up the command or event you're interested in, then
follow the references.
TODO Should we hide the type names to eliminate the temptation?
New generator scripts/qapi-introspect.py computes an introspection
value for its input, and generates a C variable holding it.
It can generate awfully long lines. Marked TODO.
A new test-qmp-input-visitor test case feeds its result for both
tests/qapi-schema/qapi-schema-test.json and qapi-schema.json to a
QmpInputVisitor to verify it actually conforms to the schema.
New QMP command query-qmp-schema takes its return value from that
variable. Its reply is some 85KiBytes for me right now.
If this turns out to be too much, we have a couple of options:
* We can use shorter names in the JSON. Not the QMP style.
* Optionally return the sub-schema for commands and events given as
arguments.
Right now qmp_query_schema() sends the string literal computed by
qmp-introspect.py. To compute sub-schema at run time, we'd have to
duplicate parts of qapi-introspect.py in C. Unattractive.
* Let clients cache the output of query-qmp-schema.
It changes only on QEMU upgrades, i.e. rarely. Provide a command
query-qmp-schema-hash. Clients can have a cache indexed by hash,
and re-query the schema only when they don't have it cached. Even
simpler: put the hash in the QMP greeting.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
2015-09-16 13:06:28 +02:00
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2016-03-17 23:48:29 +01:00
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Type "q_obj-EVENT_C-arg" is an implicitly defined object type with
|
qapi: New QMP command query-qmp-schema for QMP introspection
qapi/introspect.json defines the introspection schema. It's designed
for QMP introspection, but should do for similar uses, such as QGA.
The introspection schema does not reflect all the rules and
restrictions that apply to QAPI schemata. A valid QAPI schema has an
introspection value conforming to the introspection schema, but the
converse is not true.
Introspection lowers away a number of schema details, and makes
implicit things explicit:
* The built-in types are declared with their JSON type.
All integer types are mapped to 'int', because how many bits we use
internally is an implementation detail. It could be pressed into
external interface service as very approximate range information,
but that's a bad idea. If we need range information, we better do
it properly.
* Implicit type definitions are made explicit, and given
auto-generated names:
- Array types, named by appending "List" to the name of their
element type, like in generated C.
- The enumeration types implicitly defined by simple union types,
named by appending "Kind" to the name of their simple union type,
like in generated C.
- Types that don't occur in generated C. Their names start with ':'
so they don't clash with the user's names.
* All type references are by name.
* The struct and union types are generalized into an object type.
* Base types are flattened.
* Commands take a single argument and return a single result.
Dictionary argument or list result is an implicit type definition.
The empty object type is used when a command takes no arguments or
produces no results.
The argument is always of object type, but the introspection schema
doesn't reflect that.
The 'gen': false directive is omitted as implementation detail.
The 'success-response' directive is omitted as well for now, even
though it's not an implementation detail, because it's not used by
QMP.
* Events carry a single data value.
Implicit type definition and empty object type use, just like for
commands.
The value is of object type, but the introspection schema doesn't
reflect that.
* Types not used by commands or events are omitted.
Indirect use counts as use.
* Optional members have a default, which can only be null right now
Instead of a mandatory "optional" flag, we have an optional default.
No default means mandatory, default null means optional without
default value. Non-null is available for optional with default
(possible future extension).
* Clients should *not* look up types by name, because type names are
not ABI. Look up the command or event you're interested in, then
follow the references.
TODO Should we hide the type names to eliminate the temptation?
New generator scripts/qapi-introspect.py computes an introspection
value for its input, and generates a C variable holding it.
It can generate awfully long lines. Marked TODO.
A new test-qmp-input-visitor test case feeds its result for both
tests/qapi-schema/qapi-schema-test.json and qapi-schema.json to a
QmpInputVisitor to verify it actually conforms to the schema.
New QMP command query-qmp-schema takes its return value from that
variable. Its reply is some 85KiBytes for me right now.
If this turns out to be too much, we have a couple of options:
* We can use shorter names in the JSON. Not the QMP style.
* Optionally return the sub-schema for commands and events given as
arguments.
Right now qmp_query_schema() sends the string literal computed by
qmp-introspect.py. To compute sub-schema at run time, we'd have to
duplicate parts of qapi-introspect.py in C. Unattractive.
* Let clients cache the output of query-qmp-schema.
It changes only on QEMU upgrades, i.e. rarely. Provide a command
query-qmp-schema-hash. Clients can have a cache indexed by hash,
and re-query the schema only when they don't have it cached. Even
simpler: put the hash in the QMP greeting.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
2015-09-16 13:06:28 +02:00
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the two members from the event's definition.
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The SchemaInfo for struct and union types has meta-type "object".
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The SchemaInfo for a struct type has variant member "members".
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The SchemaInfo for a union type additionally has variant members "tag"
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and "variants".
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"members" is a JSON array describing the object's common members, if
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any. Each element is a JSON object with members "name" (the member's
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name), "type" (the name of its type), and optionally "default". The
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member is optional if "default" is present. Currently, "default" can
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only have value null. Other values are reserved for future
|
qapi-introspect: Document lack of sorting
qapi-code-gen.txt already claims that types, commands, and
events share a common namespace; set this in stone by further
documenting that our introspection output will never have
collisions with the same name tied to more than one meta-type.
Our largest QMP enum currently has 125 values, our largest
object type has 27 members, and the mean for each is less than
10. These sizes are small enough that the per-element overhead
of O(log n) binary searching probably outweighs the speed
possible with direct O(n) linear searching (a better algorithm
with more overhead will only beat a leaner naive algorithm only
as you scale to larger input sizes).
Arguably, the overall SchemaInfo array could be sorted by name;
there, we currently have 531 entities, large enough for a binary
search to be faster than linear. However, remember that we have
mutually-recursive types, which means there is no topological
ordering that will allow clients to learn all information about
that type in a single linear pass; thus clients will want to do
random access over the data, and they will probably read the
introspection output into a hashtable for O(1) lookup rather
than O(log n) binary searching, at which point, pre-sorting our
introspection output doesn't help the client.
It doesn't help that sorting can be subjective if you introduce
locales into the mix (I'm not experienced enough with Python
to know for sure, but at least it looks like it defaults to
sorting in the C locale even when run under a different locale).
And while our current introspection output is deterministic
(because we visit entities in a sorted order), we may want
to change that order in the future (such as using OrderedDict
to stick to .json declaration order).
For these reasons, we simply document that clients should not
rely on any particular order of items in introspection output.
And since it is now a documented part of the contract, we have
the freedom to later rearrange output if needed, without
worrying about breaking well-written clients.
Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1446791754-23823-13-git-send-email-eblake@redhat.com>
[Commit message tweaked]
Signed-off-by: Markus Armbruster <armbru@redhat.com>
2015-11-06 07:35:36 +01:00
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extensions. The "members" array is in no particular order; clients
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must search the entire object when learning whether a particular
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member is supported.
|
qapi: New QMP command query-qmp-schema for QMP introspection
qapi/introspect.json defines the introspection schema. It's designed
for QMP introspection, but should do for similar uses, such as QGA.
The introspection schema does not reflect all the rules and
restrictions that apply to QAPI schemata. A valid QAPI schema has an
introspection value conforming to the introspection schema, but the
converse is not true.
Introspection lowers away a number of schema details, and makes
implicit things explicit:
* The built-in types are declared with their JSON type.
All integer types are mapped to 'int', because how many bits we use
internally is an implementation detail. It could be pressed into
external interface service as very approximate range information,
but that's a bad idea. If we need range information, we better do
it properly.
* Implicit type definitions are made explicit, and given
auto-generated names:
- Array types, named by appending "List" to the name of their
element type, like in generated C.
- The enumeration types implicitly defined by simple union types,
named by appending "Kind" to the name of their simple union type,
like in generated C.
- Types that don't occur in generated C. Their names start with ':'
so they don't clash with the user's names.
* All type references are by name.
* The struct and union types are generalized into an object type.
* Base types are flattened.
* Commands take a single argument and return a single result.
Dictionary argument or list result is an implicit type definition.
The empty object type is used when a command takes no arguments or
produces no results.
The argument is always of object type, but the introspection schema
doesn't reflect that.
The 'gen': false directive is omitted as implementation detail.
The 'success-response' directive is omitted as well for now, even
though it's not an implementation detail, because it's not used by
QMP.
* Events carry a single data value.
Implicit type definition and empty object type use, just like for
commands.
The value is of object type, but the introspection schema doesn't
reflect that.
* Types not used by commands or events are omitted.
Indirect use counts as use.
* Optional members have a default, which can only be null right now
Instead of a mandatory "optional" flag, we have an optional default.
No default means mandatory, default null means optional without
default value. Non-null is available for optional with default
(possible future extension).
* Clients should *not* look up types by name, because type names are
not ABI. Look up the command or event you're interested in, then
follow the references.
TODO Should we hide the type names to eliminate the temptation?
New generator scripts/qapi-introspect.py computes an introspection
value for its input, and generates a C variable holding it.
It can generate awfully long lines. Marked TODO.
A new test-qmp-input-visitor test case feeds its result for both
tests/qapi-schema/qapi-schema-test.json and qapi-schema.json to a
QmpInputVisitor to verify it actually conforms to the schema.
New QMP command query-qmp-schema takes its return value from that
variable. Its reply is some 85KiBytes for me right now.
If this turns out to be too much, we have a couple of options:
* We can use shorter names in the JSON. Not the QMP style.
* Optionally return the sub-schema for commands and events given as
arguments.
Right now qmp_query_schema() sends the string literal computed by
qmp-introspect.py. To compute sub-schema at run time, we'd have to
duplicate parts of qapi-introspect.py in C. Unattractive.
* Let clients cache the output of query-qmp-schema.
It changes only on QEMU upgrades, i.e. rarely. Provide a command
query-qmp-schema-hash. Clients can have a cache indexed by hash,
and re-query the schema only when they don't have it cached. Even
simpler: put the hash in the QMP greeting.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
2015-09-16 13:06:28 +02:00
|
|
|
|
|
|
|
Example: the SchemaInfo for MyType from section Struct types
|
|
|
|
|
|
|
|
{ "name": "MyType", "meta-type": "object",
|
|
|
|
"members": [
|
|
|
|
{ "name": "member1", "type": "str" },
|
|
|
|
{ "name": "member2", "type": "int" },
|
|
|
|
{ "name": "member3", "type": "str", "default": null } ] }
|
|
|
|
|
|
|
|
"tag" is the name of the common member serving as type tag.
|
|
|
|
"variants" is a JSON array describing the object's variant members.
|
|
|
|
Each element is a JSON object with members "case" (the value of type
|
|
|
|
tag this element applies to) and "type" (the name of an object type
|
qapi-introspect: Document lack of sorting
qapi-code-gen.txt already claims that types, commands, and
events share a common namespace; set this in stone by further
documenting that our introspection output will never have
collisions with the same name tied to more than one meta-type.
Our largest QMP enum currently has 125 values, our largest
object type has 27 members, and the mean for each is less than
10. These sizes are small enough that the per-element overhead
of O(log n) binary searching probably outweighs the speed
possible with direct O(n) linear searching (a better algorithm
with more overhead will only beat a leaner naive algorithm only
as you scale to larger input sizes).
Arguably, the overall SchemaInfo array could be sorted by name;
there, we currently have 531 entities, large enough for a binary
search to be faster than linear. However, remember that we have
mutually-recursive types, which means there is no topological
ordering that will allow clients to learn all information about
that type in a single linear pass; thus clients will want to do
random access over the data, and they will probably read the
introspection output into a hashtable for O(1) lookup rather
than O(log n) binary searching, at which point, pre-sorting our
introspection output doesn't help the client.
It doesn't help that sorting can be subjective if you introduce
locales into the mix (I'm not experienced enough with Python
to know for sure, but at least it looks like it defaults to
sorting in the C locale even when run under a different locale).
And while our current introspection output is deterministic
(because we visit entities in a sorted order), we may want
to change that order in the future (such as using OrderedDict
to stick to .json declaration order).
For these reasons, we simply document that clients should not
rely on any particular order of items in introspection output.
And since it is now a documented part of the contract, we have
the freedom to later rearrange output if needed, without
worrying about breaking well-written clients.
Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1446791754-23823-13-git-send-email-eblake@redhat.com>
[Commit message tweaked]
Signed-off-by: Markus Armbruster <armbru@redhat.com>
2015-11-06 07:35:36 +01:00
|
|
|
that provides the variant members for this type tag value). The
|
|
|
|
"variants" array is in no particular order, and is not guaranteed to
|
|
|
|
list cases in the same order as the corresponding "tag" enum type.
|
qapi: New QMP command query-qmp-schema for QMP introspection
qapi/introspect.json defines the introspection schema. It's designed
for QMP introspection, but should do for similar uses, such as QGA.
The introspection schema does not reflect all the rules and
restrictions that apply to QAPI schemata. A valid QAPI schema has an
introspection value conforming to the introspection schema, but the
converse is not true.
Introspection lowers away a number of schema details, and makes
implicit things explicit:
* The built-in types are declared with their JSON type.
All integer types are mapped to 'int', because how many bits we use
internally is an implementation detail. It could be pressed into
external interface service as very approximate range information,
but that's a bad idea. If we need range information, we better do
it properly.
* Implicit type definitions are made explicit, and given
auto-generated names:
- Array types, named by appending "List" to the name of their
element type, like in generated C.
- The enumeration types implicitly defined by simple union types,
named by appending "Kind" to the name of their simple union type,
like in generated C.
- Types that don't occur in generated C. Their names start with ':'
so they don't clash with the user's names.
* All type references are by name.
* The struct and union types are generalized into an object type.
* Base types are flattened.
* Commands take a single argument and return a single result.
Dictionary argument or list result is an implicit type definition.
The empty object type is used when a command takes no arguments or
produces no results.
The argument is always of object type, but the introspection schema
doesn't reflect that.
The 'gen': false directive is omitted as implementation detail.
The 'success-response' directive is omitted as well for now, even
though it's not an implementation detail, because it's not used by
QMP.
* Events carry a single data value.
Implicit type definition and empty object type use, just like for
commands.
The value is of object type, but the introspection schema doesn't
reflect that.
* Types not used by commands or events are omitted.
Indirect use counts as use.
* Optional members have a default, which can only be null right now
Instead of a mandatory "optional" flag, we have an optional default.
No default means mandatory, default null means optional without
default value. Non-null is available for optional with default
(possible future extension).
* Clients should *not* look up types by name, because type names are
not ABI. Look up the command or event you're interested in, then
follow the references.
TODO Should we hide the type names to eliminate the temptation?
New generator scripts/qapi-introspect.py computes an introspection
value for its input, and generates a C variable holding it.
It can generate awfully long lines. Marked TODO.
A new test-qmp-input-visitor test case feeds its result for both
tests/qapi-schema/qapi-schema-test.json and qapi-schema.json to a
QmpInputVisitor to verify it actually conforms to the schema.
New QMP command query-qmp-schema takes its return value from that
variable. Its reply is some 85KiBytes for me right now.
If this turns out to be too much, we have a couple of options:
* We can use shorter names in the JSON. Not the QMP style.
* Optionally return the sub-schema for commands and events given as
arguments.
Right now qmp_query_schema() sends the string literal computed by
qmp-introspect.py. To compute sub-schema at run time, we'd have to
duplicate parts of qapi-introspect.py in C. Unattractive.
* Let clients cache the output of query-qmp-schema.
It changes only on QEMU upgrades, i.e. rarely. Provide a command
query-qmp-schema-hash. Clients can have a cache indexed by hash,
and re-query the schema only when they don't have it cached. Even
simpler: put the hash in the QMP greeting.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
2015-09-16 13:06:28 +02:00
|
|
|
|
|
|
|
Example: the SchemaInfo for flat union BlockdevOptions from section
|
|
|
|
Union types
|
|
|
|
|
|
|
|
{ "name": "BlockdevOptions", "meta-type": "object",
|
|
|
|
"members": [
|
|
|
|
{ "name": "driver", "type": "BlockdevDriver" },
|
2016-03-17 23:48:38 +01:00
|
|
|
{ "name": "read-only", "type": "bool", "default": null } ],
|
qapi: New QMP command query-qmp-schema for QMP introspection
qapi/introspect.json defines the introspection schema. It's designed
for QMP introspection, but should do for similar uses, such as QGA.
The introspection schema does not reflect all the rules and
restrictions that apply to QAPI schemata. A valid QAPI schema has an
introspection value conforming to the introspection schema, but the
converse is not true.
Introspection lowers away a number of schema details, and makes
implicit things explicit:
* The built-in types are declared with their JSON type.
All integer types are mapped to 'int', because how many bits we use
internally is an implementation detail. It could be pressed into
external interface service as very approximate range information,
but that's a bad idea. If we need range information, we better do
it properly.
* Implicit type definitions are made explicit, and given
auto-generated names:
- Array types, named by appending "List" to the name of their
element type, like in generated C.
- The enumeration types implicitly defined by simple union types,
named by appending "Kind" to the name of their simple union type,
like in generated C.
- Types that don't occur in generated C. Their names start with ':'
so they don't clash with the user's names.
* All type references are by name.
* The struct and union types are generalized into an object type.
* Base types are flattened.
* Commands take a single argument and return a single result.
Dictionary argument or list result is an implicit type definition.
The empty object type is used when a command takes no arguments or
produces no results.
The argument is always of object type, but the introspection schema
doesn't reflect that.
The 'gen': false directive is omitted as implementation detail.
The 'success-response' directive is omitted as well for now, even
though it's not an implementation detail, because it's not used by
QMP.
* Events carry a single data value.
Implicit type definition and empty object type use, just like for
commands.
The value is of object type, but the introspection schema doesn't
reflect that.
* Types not used by commands or events are omitted.
Indirect use counts as use.
* Optional members have a default, which can only be null right now
Instead of a mandatory "optional" flag, we have an optional default.
No default means mandatory, default null means optional without
default value. Non-null is available for optional with default
(possible future extension).
* Clients should *not* look up types by name, because type names are
not ABI. Look up the command or event you're interested in, then
follow the references.
TODO Should we hide the type names to eliminate the temptation?
New generator scripts/qapi-introspect.py computes an introspection
value for its input, and generates a C variable holding it.
It can generate awfully long lines. Marked TODO.
A new test-qmp-input-visitor test case feeds its result for both
tests/qapi-schema/qapi-schema-test.json and qapi-schema.json to a
QmpInputVisitor to verify it actually conforms to the schema.
New QMP command query-qmp-schema takes its return value from that
variable. Its reply is some 85KiBytes for me right now.
If this turns out to be too much, we have a couple of options:
* We can use shorter names in the JSON. Not the QMP style.
* Optionally return the sub-schema for commands and events given as
arguments.
Right now qmp_query_schema() sends the string literal computed by
qmp-introspect.py. To compute sub-schema at run time, we'd have to
duplicate parts of qapi-introspect.py in C. Unattractive.
* Let clients cache the output of query-qmp-schema.
It changes only on QEMU upgrades, i.e. rarely. Provide a command
query-qmp-schema-hash. Clients can have a cache indexed by hash,
and re-query the schema only when they don't have it cached. Even
simpler: put the hash in the QMP greeting.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
2015-09-16 13:06:28 +02:00
|
|
|
"tag": "driver",
|
|
|
|
"variants": [
|
2016-03-17 23:48:38 +01:00
|
|
|
{ "case": "file", "type": "BlockdevOptionsFile" },
|
|
|
|
{ "case": "qcow2", "type": "BlockdevOptionsQcow2" } ] }
|
qapi: New QMP command query-qmp-schema for QMP introspection
qapi/introspect.json defines the introspection schema. It's designed
for QMP introspection, but should do for similar uses, such as QGA.
The introspection schema does not reflect all the rules and
restrictions that apply to QAPI schemata. A valid QAPI schema has an
introspection value conforming to the introspection schema, but the
converse is not true.
Introspection lowers away a number of schema details, and makes
implicit things explicit:
* The built-in types are declared with their JSON type.
All integer types are mapped to 'int', because how many bits we use
internally is an implementation detail. It could be pressed into
external interface service as very approximate range information,
but that's a bad idea. If we need range information, we better do
it properly.
* Implicit type definitions are made explicit, and given
auto-generated names:
- Array types, named by appending "List" to the name of their
element type, like in generated C.
- The enumeration types implicitly defined by simple union types,
named by appending "Kind" to the name of their simple union type,
like in generated C.
- Types that don't occur in generated C. Their names start with ':'
so they don't clash with the user's names.
* All type references are by name.
* The struct and union types are generalized into an object type.
* Base types are flattened.
* Commands take a single argument and return a single result.
Dictionary argument or list result is an implicit type definition.
The empty object type is used when a command takes no arguments or
produces no results.
The argument is always of object type, but the introspection schema
doesn't reflect that.
The 'gen': false directive is omitted as implementation detail.
The 'success-response' directive is omitted as well for now, even
though it's not an implementation detail, because it's not used by
QMP.
* Events carry a single data value.
Implicit type definition and empty object type use, just like for
commands.
The value is of object type, but the introspection schema doesn't
reflect that.
* Types not used by commands or events are omitted.
Indirect use counts as use.
* Optional members have a default, which can only be null right now
Instead of a mandatory "optional" flag, we have an optional default.
No default means mandatory, default null means optional without
default value. Non-null is available for optional with default
(possible future extension).
* Clients should *not* look up types by name, because type names are
not ABI. Look up the command or event you're interested in, then
follow the references.
TODO Should we hide the type names to eliminate the temptation?
New generator scripts/qapi-introspect.py computes an introspection
value for its input, and generates a C variable holding it.
It can generate awfully long lines. Marked TODO.
A new test-qmp-input-visitor test case feeds its result for both
tests/qapi-schema/qapi-schema-test.json and qapi-schema.json to a
QmpInputVisitor to verify it actually conforms to the schema.
New QMP command query-qmp-schema takes its return value from that
variable. Its reply is some 85KiBytes for me right now.
If this turns out to be too much, we have a couple of options:
* We can use shorter names in the JSON. Not the QMP style.
* Optionally return the sub-schema for commands and events given as
arguments.
Right now qmp_query_schema() sends the string literal computed by
qmp-introspect.py. To compute sub-schema at run time, we'd have to
duplicate parts of qapi-introspect.py in C. Unattractive.
* Let clients cache the output of query-qmp-schema.
It changes only on QEMU upgrades, i.e. rarely. Provide a command
query-qmp-schema-hash. Clients can have a cache indexed by hash,
and re-query the schema only when they don't have it cached. Even
simpler: put the hash in the QMP greeting.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
2015-09-16 13:06:28 +02:00
|
|
|
|
|
|
|
Note that base types are "flattened": its members are included in the
|
|
|
|
"members" array.
|
|
|
|
|
|
|
|
A simple union implicitly defines an enumeration type for its implicit
|
|
|
|
discriminator (called "type" on the wire, see section Union types).
|
|
|
|
|
|
|
|
A simple union implicitly defines an object type for each of its
|
2015-09-16 13:06:29 +02:00
|
|
|
variants.
|
qapi: New QMP command query-qmp-schema for QMP introspection
qapi/introspect.json defines the introspection schema. It's designed
for QMP introspection, but should do for similar uses, such as QGA.
The introspection schema does not reflect all the rules and
restrictions that apply to QAPI schemata. A valid QAPI schema has an
introspection value conforming to the introspection schema, but the
converse is not true.
Introspection lowers away a number of schema details, and makes
implicit things explicit:
* The built-in types are declared with their JSON type.
All integer types are mapped to 'int', because how many bits we use
internally is an implementation detail. It could be pressed into
external interface service as very approximate range information,
but that's a bad idea. If we need range information, we better do
it properly.
* Implicit type definitions are made explicit, and given
auto-generated names:
- Array types, named by appending "List" to the name of their
element type, like in generated C.
- The enumeration types implicitly defined by simple union types,
named by appending "Kind" to the name of their simple union type,
like in generated C.
- Types that don't occur in generated C. Their names start with ':'
so they don't clash with the user's names.
* All type references are by name.
* The struct and union types are generalized into an object type.
* Base types are flattened.
* Commands take a single argument and return a single result.
Dictionary argument or list result is an implicit type definition.
The empty object type is used when a command takes no arguments or
produces no results.
The argument is always of object type, but the introspection schema
doesn't reflect that.
The 'gen': false directive is omitted as implementation detail.
The 'success-response' directive is omitted as well for now, even
though it's not an implementation detail, because it's not used by
QMP.
* Events carry a single data value.
Implicit type definition and empty object type use, just like for
commands.
The value is of object type, but the introspection schema doesn't
reflect that.
* Types not used by commands or events are omitted.
Indirect use counts as use.
* Optional members have a default, which can only be null right now
Instead of a mandatory "optional" flag, we have an optional default.
No default means mandatory, default null means optional without
default value. Non-null is available for optional with default
(possible future extension).
* Clients should *not* look up types by name, because type names are
not ABI. Look up the command or event you're interested in, then
follow the references.
TODO Should we hide the type names to eliminate the temptation?
New generator scripts/qapi-introspect.py computes an introspection
value for its input, and generates a C variable holding it.
It can generate awfully long lines. Marked TODO.
A new test-qmp-input-visitor test case feeds its result for both
tests/qapi-schema/qapi-schema-test.json and qapi-schema.json to a
QmpInputVisitor to verify it actually conforms to the schema.
New QMP command query-qmp-schema takes its return value from that
variable. Its reply is some 85KiBytes for me right now.
If this turns out to be too much, we have a couple of options:
* We can use shorter names in the JSON. Not the QMP style.
* Optionally return the sub-schema for commands and events given as
arguments.
Right now qmp_query_schema() sends the string literal computed by
qmp-introspect.py. To compute sub-schema at run time, we'd have to
duplicate parts of qapi-introspect.py in C. Unattractive.
* Let clients cache the output of query-qmp-schema.
It changes only on QEMU upgrades, i.e. rarely. Provide a command
query-qmp-schema-hash. Clients can have a cache indexed by hash,
and re-query the schema only when they don't have it cached. Even
simpler: put the hash in the QMP greeting.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
2015-09-16 13:06:28 +02:00
|
|
|
|
2016-03-17 23:48:38 +01:00
|
|
|
Example: the SchemaInfo for simple union BlockdevOptionsSimple from section
|
qapi: New QMP command query-qmp-schema for QMP introspection
qapi/introspect.json defines the introspection schema. It's designed
for QMP introspection, but should do for similar uses, such as QGA.
The introspection schema does not reflect all the rules and
restrictions that apply to QAPI schemata. A valid QAPI schema has an
introspection value conforming to the introspection schema, but the
converse is not true.
Introspection lowers away a number of schema details, and makes
implicit things explicit:
* The built-in types are declared with their JSON type.
All integer types are mapped to 'int', because how many bits we use
internally is an implementation detail. It could be pressed into
external interface service as very approximate range information,
but that's a bad idea. If we need range information, we better do
it properly.
* Implicit type definitions are made explicit, and given
auto-generated names:
- Array types, named by appending "List" to the name of their
element type, like in generated C.
- The enumeration types implicitly defined by simple union types,
named by appending "Kind" to the name of their simple union type,
like in generated C.
- Types that don't occur in generated C. Their names start with ':'
so they don't clash with the user's names.
* All type references are by name.
* The struct and union types are generalized into an object type.
* Base types are flattened.
* Commands take a single argument and return a single result.
Dictionary argument or list result is an implicit type definition.
The empty object type is used when a command takes no arguments or
produces no results.
The argument is always of object type, but the introspection schema
doesn't reflect that.
The 'gen': false directive is omitted as implementation detail.
The 'success-response' directive is omitted as well for now, even
though it's not an implementation detail, because it's not used by
QMP.
* Events carry a single data value.
Implicit type definition and empty object type use, just like for
commands.
The value is of object type, but the introspection schema doesn't
reflect that.
* Types not used by commands or events are omitted.
Indirect use counts as use.
* Optional members have a default, which can only be null right now
Instead of a mandatory "optional" flag, we have an optional default.
No default means mandatory, default null means optional without
default value. Non-null is available for optional with default
(possible future extension).
* Clients should *not* look up types by name, because type names are
not ABI. Look up the command or event you're interested in, then
follow the references.
TODO Should we hide the type names to eliminate the temptation?
New generator scripts/qapi-introspect.py computes an introspection
value for its input, and generates a C variable holding it.
It can generate awfully long lines. Marked TODO.
A new test-qmp-input-visitor test case feeds its result for both
tests/qapi-schema/qapi-schema-test.json and qapi-schema.json to a
QmpInputVisitor to verify it actually conforms to the schema.
New QMP command query-qmp-schema takes its return value from that
variable. Its reply is some 85KiBytes for me right now.
If this turns out to be too much, we have a couple of options:
* We can use shorter names in the JSON. Not the QMP style.
* Optionally return the sub-schema for commands and events given as
arguments.
Right now qmp_query_schema() sends the string literal computed by
qmp-introspect.py. To compute sub-schema at run time, we'd have to
duplicate parts of qapi-introspect.py in C. Unattractive.
* Let clients cache the output of query-qmp-schema.
It changes only on QEMU upgrades, i.e. rarely. Provide a command
query-qmp-schema-hash. Clients can have a cache indexed by hash,
and re-query the schema only when they don't have it cached. Even
simpler: put the hash in the QMP greeting.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
2015-09-16 13:06:28 +02:00
|
|
|
Union types
|
|
|
|
|
2016-03-17 23:48:38 +01:00
|
|
|
{ "name": "BlockdevOptionsSimple", "meta-type": "object",
|
qapi: New QMP command query-qmp-schema for QMP introspection
qapi/introspect.json defines the introspection schema. It's designed
for QMP introspection, but should do for similar uses, such as QGA.
The introspection schema does not reflect all the rules and
restrictions that apply to QAPI schemata. A valid QAPI schema has an
introspection value conforming to the introspection schema, but the
converse is not true.
Introspection lowers away a number of schema details, and makes
implicit things explicit:
* The built-in types are declared with their JSON type.
All integer types are mapped to 'int', because how many bits we use
internally is an implementation detail. It could be pressed into
external interface service as very approximate range information,
but that's a bad idea. If we need range information, we better do
it properly.
* Implicit type definitions are made explicit, and given
auto-generated names:
- Array types, named by appending "List" to the name of their
element type, like in generated C.
- The enumeration types implicitly defined by simple union types,
named by appending "Kind" to the name of their simple union type,
like in generated C.
- Types that don't occur in generated C. Their names start with ':'
so they don't clash with the user's names.
* All type references are by name.
* The struct and union types are generalized into an object type.
* Base types are flattened.
* Commands take a single argument and return a single result.
Dictionary argument or list result is an implicit type definition.
The empty object type is used when a command takes no arguments or
produces no results.
The argument is always of object type, but the introspection schema
doesn't reflect that.
The 'gen': false directive is omitted as implementation detail.
The 'success-response' directive is omitted as well for now, even
though it's not an implementation detail, because it's not used by
QMP.
* Events carry a single data value.
Implicit type definition and empty object type use, just like for
commands.
The value is of object type, but the introspection schema doesn't
reflect that.
* Types not used by commands or events are omitted.
Indirect use counts as use.
* Optional members have a default, which can only be null right now
Instead of a mandatory "optional" flag, we have an optional default.
No default means mandatory, default null means optional without
default value. Non-null is available for optional with default
(possible future extension).
* Clients should *not* look up types by name, because type names are
not ABI. Look up the command or event you're interested in, then
follow the references.
TODO Should we hide the type names to eliminate the temptation?
New generator scripts/qapi-introspect.py computes an introspection
value for its input, and generates a C variable holding it.
It can generate awfully long lines. Marked TODO.
A new test-qmp-input-visitor test case feeds its result for both
tests/qapi-schema/qapi-schema-test.json and qapi-schema.json to a
QmpInputVisitor to verify it actually conforms to the schema.
New QMP command query-qmp-schema takes its return value from that
variable. Its reply is some 85KiBytes for me right now.
If this turns out to be too much, we have a couple of options:
* We can use shorter names in the JSON. Not the QMP style.
* Optionally return the sub-schema for commands and events given as
arguments.
Right now qmp_query_schema() sends the string literal computed by
qmp-introspect.py. To compute sub-schema at run time, we'd have to
duplicate parts of qapi-introspect.py in C. Unattractive.
* Let clients cache the output of query-qmp-schema.
It changes only on QEMU upgrades, i.e. rarely. Provide a command
query-qmp-schema-hash. Clients can have a cache indexed by hash,
and re-query the schema only when they don't have it cached. Even
simpler: put the hash in the QMP greeting.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
2015-09-16 13:06:28 +02:00
|
|
|
"members": [
|
2016-03-17 23:48:38 +01:00
|
|
|
{ "name": "type", "type": "BlockdevOptionsSimpleKind" } ],
|
qapi: New QMP command query-qmp-schema for QMP introspection
qapi/introspect.json defines the introspection schema. It's designed
for QMP introspection, but should do for similar uses, such as QGA.
The introspection schema does not reflect all the rules and
restrictions that apply to QAPI schemata. A valid QAPI schema has an
introspection value conforming to the introspection schema, but the
converse is not true.
Introspection lowers away a number of schema details, and makes
implicit things explicit:
* The built-in types are declared with their JSON type.
All integer types are mapped to 'int', because how many bits we use
internally is an implementation detail. It could be pressed into
external interface service as very approximate range information,
but that's a bad idea. If we need range information, we better do
it properly.
* Implicit type definitions are made explicit, and given
auto-generated names:
- Array types, named by appending "List" to the name of their
element type, like in generated C.
- The enumeration types implicitly defined by simple union types,
named by appending "Kind" to the name of their simple union type,
like in generated C.
- Types that don't occur in generated C. Their names start with ':'
so they don't clash with the user's names.
* All type references are by name.
* The struct and union types are generalized into an object type.
* Base types are flattened.
* Commands take a single argument and return a single result.
Dictionary argument or list result is an implicit type definition.
The empty object type is used when a command takes no arguments or
produces no results.
The argument is always of object type, but the introspection schema
doesn't reflect that.
The 'gen': false directive is omitted as implementation detail.
The 'success-response' directive is omitted as well for now, even
though it's not an implementation detail, because it's not used by
QMP.
* Events carry a single data value.
Implicit type definition and empty object type use, just like for
commands.
The value is of object type, but the introspection schema doesn't
reflect that.
* Types not used by commands or events are omitted.
Indirect use counts as use.
* Optional members have a default, which can only be null right now
Instead of a mandatory "optional" flag, we have an optional default.
No default means mandatory, default null means optional without
default value. Non-null is available for optional with default
(possible future extension).
* Clients should *not* look up types by name, because type names are
not ABI. Look up the command or event you're interested in, then
follow the references.
TODO Should we hide the type names to eliminate the temptation?
New generator scripts/qapi-introspect.py computes an introspection
value for its input, and generates a C variable holding it.
It can generate awfully long lines. Marked TODO.
A new test-qmp-input-visitor test case feeds its result for both
tests/qapi-schema/qapi-schema-test.json and qapi-schema.json to a
QmpInputVisitor to verify it actually conforms to the schema.
New QMP command query-qmp-schema takes its return value from that
variable. Its reply is some 85KiBytes for me right now.
If this turns out to be too much, we have a couple of options:
* We can use shorter names in the JSON. Not the QMP style.
* Optionally return the sub-schema for commands and events given as
arguments.
Right now qmp_query_schema() sends the string literal computed by
qmp-introspect.py. To compute sub-schema at run time, we'd have to
duplicate parts of qapi-introspect.py in C. Unattractive.
* Let clients cache the output of query-qmp-schema.
It changes only on QEMU upgrades, i.e. rarely. Provide a command
query-qmp-schema-hash. Clients can have a cache indexed by hash,
and re-query the schema only when they don't have it cached. Even
simpler: put the hash in the QMP greeting.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
2015-09-16 13:06:28 +02:00
|
|
|
"tag": "type",
|
|
|
|
"variants": [
|
2016-03-17 23:48:38 +01:00
|
|
|
{ "case": "file", "type": "q_obj-BlockdevOptionsFile-wrapper" },
|
|
|
|
{ "case": "qcow2", "type": "q_obj-BlockdevOptionsQcow2-wrapper" } ] }
|
qapi: New QMP command query-qmp-schema for QMP introspection
qapi/introspect.json defines the introspection schema. It's designed
for QMP introspection, but should do for similar uses, such as QGA.
The introspection schema does not reflect all the rules and
restrictions that apply to QAPI schemata. A valid QAPI schema has an
introspection value conforming to the introspection schema, but the
converse is not true.
Introspection lowers away a number of schema details, and makes
implicit things explicit:
* The built-in types are declared with their JSON type.
All integer types are mapped to 'int', because how many bits we use
internally is an implementation detail. It could be pressed into
external interface service as very approximate range information,
but that's a bad idea. If we need range information, we better do
it properly.
* Implicit type definitions are made explicit, and given
auto-generated names:
- Array types, named by appending "List" to the name of their
element type, like in generated C.
- The enumeration types implicitly defined by simple union types,
named by appending "Kind" to the name of their simple union type,
like in generated C.
- Types that don't occur in generated C. Their names start with ':'
so they don't clash with the user's names.
* All type references are by name.
* The struct and union types are generalized into an object type.
* Base types are flattened.
* Commands take a single argument and return a single result.
Dictionary argument or list result is an implicit type definition.
The empty object type is used when a command takes no arguments or
produces no results.
The argument is always of object type, but the introspection schema
doesn't reflect that.
The 'gen': false directive is omitted as implementation detail.
The 'success-response' directive is omitted as well for now, even
though it's not an implementation detail, because it's not used by
QMP.
* Events carry a single data value.
Implicit type definition and empty object type use, just like for
commands.
The value is of object type, but the introspection schema doesn't
reflect that.
* Types not used by commands or events are omitted.
Indirect use counts as use.
* Optional members have a default, which can only be null right now
Instead of a mandatory "optional" flag, we have an optional default.
No default means mandatory, default null means optional without
default value. Non-null is available for optional with default
(possible future extension).
* Clients should *not* look up types by name, because type names are
not ABI. Look up the command or event you're interested in, then
follow the references.
TODO Should we hide the type names to eliminate the temptation?
New generator scripts/qapi-introspect.py computes an introspection
value for its input, and generates a C variable holding it.
It can generate awfully long lines. Marked TODO.
A new test-qmp-input-visitor test case feeds its result for both
tests/qapi-schema/qapi-schema-test.json and qapi-schema.json to a
QmpInputVisitor to verify it actually conforms to the schema.
New QMP command query-qmp-schema takes its return value from that
variable. Its reply is some 85KiBytes for me right now.
If this turns out to be too much, we have a couple of options:
* We can use shorter names in the JSON. Not the QMP style.
* Optionally return the sub-schema for commands and events given as
arguments.
Right now qmp_query_schema() sends the string literal computed by
qmp-introspect.py. To compute sub-schema at run time, we'd have to
duplicate parts of qapi-introspect.py in C. Unattractive.
* Let clients cache the output of query-qmp-schema.
It changes only on QEMU upgrades, i.e. rarely. Provide a command
query-qmp-schema-hash. Clients can have a cache indexed by hash,
and re-query the schema only when they don't have it cached. Even
simpler: put the hash in the QMP greeting.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
2015-09-16 13:06:28 +02:00
|
|
|
|
2016-03-17 23:48:38 +01:00
|
|
|
Enumeration type "BlockdevOptionsSimpleKind" and the object types
|
|
|
|
"q_obj-BlockdevOptionsFile-wrapper", "q_obj-BlockdevOptionsQcow2-wrapper"
|
|
|
|
are implicitly defined.
|
qapi: New QMP command query-qmp-schema for QMP introspection
qapi/introspect.json defines the introspection schema. It's designed
for QMP introspection, but should do for similar uses, such as QGA.
The introspection schema does not reflect all the rules and
restrictions that apply to QAPI schemata. A valid QAPI schema has an
introspection value conforming to the introspection schema, but the
converse is not true.
Introspection lowers away a number of schema details, and makes
implicit things explicit:
* The built-in types are declared with their JSON type.
All integer types are mapped to 'int', because how many bits we use
internally is an implementation detail. It could be pressed into
external interface service as very approximate range information,
but that's a bad idea. If we need range information, we better do
it properly.
* Implicit type definitions are made explicit, and given
auto-generated names:
- Array types, named by appending "List" to the name of their
element type, like in generated C.
- The enumeration types implicitly defined by simple union types,
named by appending "Kind" to the name of their simple union type,
like in generated C.
- Types that don't occur in generated C. Their names start with ':'
so they don't clash with the user's names.
* All type references are by name.
* The struct and union types are generalized into an object type.
* Base types are flattened.
* Commands take a single argument and return a single result.
Dictionary argument or list result is an implicit type definition.
The empty object type is used when a command takes no arguments or
produces no results.
The argument is always of object type, but the introspection schema
doesn't reflect that.
The 'gen': false directive is omitted as implementation detail.
The 'success-response' directive is omitted as well for now, even
though it's not an implementation detail, because it's not used by
QMP.
* Events carry a single data value.
Implicit type definition and empty object type use, just like for
commands.
The value is of object type, but the introspection schema doesn't
reflect that.
* Types not used by commands or events are omitted.
Indirect use counts as use.
* Optional members have a default, which can only be null right now
Instead of a mandatory "optional" flag, we have an optional default.
No default means mandatory, default null means optional without
default value. Non-null is available for optional with default
(possible future extension).
* Clients should *not* look up types by name, because type names are
not ABI. Look up the command or event you're interested in, then
follow the references.
TODO Should we hide the type names to eliminate the temptation?
New generator scripts/qapi-introspect.py computes an introspection
value for its input, and generates a C variable holding it.
It can generate awfully long lines. Marked TODO.
A new test-qmp-input-visitor test case feeds its result for both
tests/qapi-schema/qapi-schema-test.json and qapi-schema.json to a
QmpInputVisitor to verify it actually conforms to the schema.
New QMP command query-qmp-schema takes its return value from that
variable. Its reply is some 85KiBytes for me right now.
If this turns out to be too much, we have a couple of options:
* We can use shorter names in the JSON. Not the QMP style.
* Optionally return the sub-schema for commands and events given as
arguments.
Right now qmp_query_schema() sends the string literal computed by
qmp-introspect.py. To compute sub-schema at run time, we'd have to
duplicate parts of qapi-introspect.py in C. Unattractive.
* Let clients cache the output of query-qmp-schema.
It changes only on QEMU upgrades, i.e. rarely. Provide a command
query-qmp-schema-hash. Clients can have a cache indexed by hash,
and re-query the schema only when they don't have it cached. Even
simpler: put the hash in the QMP greeting.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
2015-09-16 13:06:28 +02:00
|
|
|
|
|
|
|
The SchemaInfo for an alternate type has meta-type "alternate", and
|
|
|
|
variant member "members". "members" is a JSON array. Each element is
|
|
|
|
a JSON object with member "type", which names a type. Values of the
|
qapi-introspect: Document lack of sorting
qapi-code-gen.txt already claims that types, commands, and
events share a common namespace; set this in stone by further
documenting that our introspection output will never have
collisions with the same name tied to more than one meta-type.
Our largest QMP enum currently has 125 values, our largest
object type has 27 members, and the mean for each is less than
10. These sizes are small enough that the per-element overhead
of O(log n) binary searching probably outweighs the speed
possible with direct O(n) linear searching (a better algorithm
with more overhead will only beat a leaner naive algorithm only
as you scale to larger input sizes).
Arguably, the overall SchemaInfo array could be sorted by name;
there, we currently have 531 entities, large enough for a binary
search to be faster than linear. However, remember that we have
mutually-recursive types, which means there is no topological
ordering that will allow clients to learn all information about
that type in a single linear pass; thus clients will want to do
random access over the data, and they will probably read the
introspection output into a hashtable for O(1) lookup rather
than O(log n) binary searching, at which point, pre-sorting our
introspection output doesn't help the client.
It doesn't help that sorting can be subjective if you introduce
locales into the mix (I'm not experienced enough with Python
to know for sure, but at least it looks like it defaults to
sorting in the C locale even when run under a different locale).
And while our current introspection output is deterministic
(because we visit entities in a sorted order), we may want
to change that order in the future (such as using OrderedDict
to stick to .json declaration order).
For these reasons, we simply document that clients should not
rely on any particular order of items in introspection output.
And since it is now a documented part of the contract, we have
the freedom to later rearrange output if needed, without
worrying about breaking well-written clients.
Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1446791754-23823-13-git-send-email-eblake@redhat.com>
[Commit message tweaked]
Signed-off-by: Markus Armbruster <armbru@redhat.com>
2015-11-06 07:35:36 +01:00
|
|
|
alternate type conform to exactly one of its member types. There is
|
|
|
|
no guarantee on the order in which "members" will be listed.
|
qapi: New QMP command query-qmp-schema for QMP introspection
qapi/introspect.json defines the introspection schema. It's designed
for QMP introspection, but should do for similar uses, such as QGA.
The introspection schema does not reflect all the rules and
restrictions that apply to QAPI schemata. A valid QAPI schema has an
introspection value conforming to the introspection schema, but the
converse is not true.
Introspection lowers away a number of schema details, and makes
implicit things explicit:
* The built-in types are declared with their JSON type.
All integer types are mapped to 'int', because how many bits we use
internally is an implementation detail. It could be pressed into
external interface service as very approximate range information,
but that's a bad idea. If we need range information, we better do
it properly.
* Implicit type definitions are made explicit, and given
auto-generated names:
- Array types, named by appending "List" to the name of their
element type, like in generated C.
- The enumeration types implicitly defined by simple union types,
named by appending "Kind" to the name of their simple union type,
like in generated C.
- Types that don't occur in generated C. Their names start with ':'
so they don't clash with the user's names.
* All type references are by name.
* The struct and union types are generalized into an object type.
* Base types are flattened.
* Commands take a single argument and return a single result.
Dictionary argument or list result is an implicit type definition.
The empty object type is used when a command takes no arguments or
produces no results.
The argument is always of object type, but the introspection schema
doesn't reflect that.
The 'gen': false directive is omitted as implementation detail.
The 'success-response' directive is omitted as well for now, even
though it's not an implementation detail, because it's not used by
QMP.
* Events carry a single data value.
Implicit type definition and empty object type use, just like for
commands.
The value is of object type, but the introspection schema doesn't
reflect that.
* Types not used by commands or events are omitted.
Indirect use counts as use.
* Optional members have a default, which can only be null right now
Instead of a mandatory "optional" flag, we have an optional default.
No default means mandatory, default null means optional without
default value. Non-null is available for optional with default
(possible future extension).
* Clients should *not* look up types by name, because type names are
not ABI. Look up the command or event you're interested in, then
follow the references.
TODO Should we hide the type names to eliminate the temptation?
New generator scripts/qapi-introspect.py computes an introspection
value for its input, and generates a C variable holding it.
It can generate awfully long lines. Marked TODO.
A new test-qmp-input-visitor test case feeds its result for both
tests/qapi-schema/qapi-schema-test.json and qapi-schema.json to a
QmpInputVisitor to verify it actually conforms to the schema.
New QMP command query-qmp-schema takes its return value from that
variable. Its reply is some 85KiBytes for me right now.
If this turns out to be too much, we have a couple of options:
* We can use shorter names in the JSON. Not the QMP style.
* Optionally return the sub-schema for commands and events given as
arguments.
Right now qmp_query_schema() sends the string literal computed by
qmp-introspect.py. To compute sub-schema at run time, we'd have to
duplicate parts of qapi-introspect.py in C. Unattractive.
* Let clients cache the output of query-qmp-schema.
It changes only on QEMU upgrades, i.e. rarely. Provide a command
query-qmp-schema-hash. Clients can have a cache indexed by hash,
and re-query the schema only when they don't have it cached. Even
simpler: put the hash in the QMP greeting.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
2015-09-16 13:06:28 +02:00
|
|
|
|
2016-03-17 23:48:38 +01:00
|
|
|
Example: the SchemaInfo for BlockdevRef from section Alternate types
|
qapi: New QMP command query-qmp-schema for QMP introspection
qapi/introspect.json defines the introspection schema. It's designed
for QMP introspection, but should do for similar uses, such as QGA.
The introspection schema does not reflect all the rules and
restrictions that apply to QAPI schemata. A valid QAPI schema has an
introspection value conforming to the introspection schema, but the
converse is not true.
Introspection lowers away a number of schema details, and makes
implicit things explicit:
* The built-in types are declared with their JSON type.
All integer types are mapped to 'int', because how many bits we use
internally is an implementation detail. It could be pressed into
external interface service as very approximate range information,
but that's a bad idea. If we need range information, we better do
it properly.
* Implicit type definitions are made explicit, and given
auto-generated names:
- Array types, named by appending "List" to the name of their
element type, like in generated C.
- The enumeration types implicitly defined by simple union types,
named by appending "Kind" to the name of their simple union type,
like in generated C.
- Types that don't occur in generated C. Their names start with ':'
so they don't clash with the user's names.
* All type references are by name.
* The struct and union types are generalized into an object type.
* Base types are flattened.
* Commands take a single argument and return a single result.
Dictionary argument or list result is an implicit type definition.
The empty object type is used when a command takes no arguments or
produces no results.
The argument is always of object type, but the introspection schema
doesn't reflect that.
The 'gen': false directive is omitted as implementation detail.
The 'success-response' directive is omitted as well for now, even
though it's not an implementation detail, because it's not used by
QMP.
* Events carry a single data value.
Implicit type definition and empty object type use, just like for
commands.
The value is of object type, but the introspection schema doesn't
reflect that.
* Types not used by commands or events are omitted.
Indirect use counts as use.
* Optional members have a default, which can only be null right now
Instead of a mandatory "optional" flag, we have an optional default.
No default means mandatory, default null means optional without
default value. Non-null is available for optional with default
(possible future extension).
* Clients should *not* look up types by name, because type names are
not ABI. Look up the command or event you're interested in, then
follow the references.
TODO Should we hide the type names to eliminate the temptation?
New generator scripts/qapi-introspect.py computes an introspection
value for its input, and generates a C variable holding it.
It can generate awfully long lines. Marked TODO.
A new test-qmp-input-visitor test case feeds its result for both
tests/qapi-schema/qapi-schema-test.json and qapi-schema.json to a
QmpInputVisitor to verify it actually conforms to the schema.
New QMP command query-qmp-schema takes its return value from that
variable. Its reply is some 85KiBytes for me right now.
If this turns out to be too much, we have a couple of options:
* We can use shorter names in the JSON. Not the QMP style.
* Optionally return the sub-schema for commands and events given as
arguments.
Right now qmp_query_schema() sends the string literal computed by
qmp-introspect.py. To compute sub-schema at run time, we'd have to
duplicate parts of qapi-introspect.py in C. Unattractive.
* Let clients cache the output of query-qmp-schema.
It changes only on QEMU upgrades, i.e. rarely. Provide a command
query-qmp-schema-hash. Clients can have a cache indexed by hash,
and re-query the schema only when they don't have it cached. Even
simpler: put the hash in the QMP greeting.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
2015-09-16 13:06:28 +02:00
|
|
|
|
2016-03-17 23:48:38 +01:00
|
|
|
{ "name": "BlockdevRef", "meta-type": "alternate",
|
qapi: New QMP command query-qmp-schema for QMP introspection
qapi/introspect.json defines the introspection schema. It's designed
for QMP introspection, but should do for similar uses, such as QGA.
The introspection schema does not reflect all the rules and
restrictions that apply to QAPI schemata. A valid QAPI schema has an
introspection value conforming to the introspection schema, but the
converse is not true.
Introspection lowers away a number of schema details, and makes
implicit things explicit:
* The built-in types are declared with their JSON type.
All integer types are mapped to 'int', because how many bits we use
internally is an implementation detail. It could be pressed into
external interface service as very approximate range information,
but that's a bad idea. If we need range information, we better do
it properly.
* Implicit type definitions are made explicit, and given
auto-generated names:
- Array types, named by appending "List" to the name of their
element type, like in generated C.
- The enumeration types implicitly defined by simple union types,
named by appending "Kind" to the name of their simple union type,
like in generated C.
- Types that don't occur in generated C. Their names start with ':'
so they don't clash with the user's names.
* All type references are by name.
* The struct and union types are generalized into an object type.
* Base types are flattened.
* Commands take a single argument and return a single result.
Dictionary argument or list result is an implicit type definition.
The empty object type is used when a command takes no arguments or
produces no results.
The argument is always of object type, but the introspection schema
doesn't reflect that.
The 'gen': false directive is omitted as implementation detail.
The 'success-response' directive is omitted as well for now, even
though it's not an implementation detail, because it's not used by
QMP.
* Events carry a single data value.
Implicit type definition and empty object type use, just like for
commands.
The value is of object type, but the introspection schema doesn't
reflect that.
* Types not used by commands or events are omitted.
Indirect use counts as use.
* Optional members have a default, which can only be null right now
Instead of a mandatory "optional" flag, we have an optional default.
No default means mandatory, default null means optional without
default value. Non-null is available for optional with default
(possible future extension).
* Clients should *not* look up types by name, because type names are
not ABI. Look up the command or event you're interested in, then
follow the references.
TODO Should we hide the type names to eliminate the temptation?
New generator scripts/qapi-introspect.py computes an introspection
value for its input, and generates a C variable holding it.
It can generate awfully long lines. Marked TODO.
A new test-qmp-input-visitor test case feeds its result for both
tests/qapi-schema/qapi-schema-test.json and qapi-schema.json to a
QmpInputVisitor to verify it actually conforms to the schema.
New QMP command query-qmp-schema takes its return value from that
variable. Its reply is some 85KiBytes for me right now.
If this turns out to be too much, we have a couple of options:
* We can use shorter names in the JSON. Not the QMP style.
* Optionally return the sub-schema for commands and events given as
arguments.
Right now qmp_query_schema() sends the string literal computed by
qmp-introspect.py. To compute sub-schema at run time, we'd have to
duplicate parts of qapi-introspect.py in C. Unattractive.
* Let clients cache the output of query-qmp-schema.
It changes only on QEMU upgrades, i.e. rarely. Provide a command
query-qmp-schema-hash. Clients can have a cache indexed by hash,
and re-query the schema only when they don't have it cached. Even
simpler: put the hash in the QMP greeting.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
2015-09-16 13:06:28 +02:00
|
|
|
"members": [
|
|
|
|
{ "type": "BlockdevOptions" },
|
|
|
|
{ "type": "str" } ] }
|
|
|
|
|
|
|
|
The SchemaInfo for an array type has meta-type "array", and variant
|
|
|
|
member "element-type", which names the array's element type. Array
|
2015-11-06 07:35:35 +01:00
|
|
|
types are implicitly defined. For convenience, the array's name may
|
|
|
|
resemble the element type; however, clients should examine member
|
|
|
|
"element-type" instead of making assumptions based on parsing member
|
|
|
|
"name".
|
qapi: New QMP command query-qmp-schema for QMP introspection
qapi/introspect.json defines the introspection schema. It's designed
for QMP introspection, but should do for similar uses, such as QGA.
The introspection schema does not reflect all the rules and
restrictions that apply to QAPI schemata. A valid QAPI schema has an
introspection value conforming to the introspection schema, but the
converse is not true.
Introspection lowers away a number of schema details, and makes
implicit things explicit:
* The built-in types are declared with their JSON type.
All integer types are mapped to 'int', because how many bits we use
internally is an implementation detail. It could be pressed into
external interface service as very approximate range information,
but that's a bad idea. If we need range information, we better do
it properly.
* Implicit type definitions are made explicit, and given
auto-generated names:
- Array types, named by appending "List" to the name of their
element type, like in generated C.
- The enumeration types implicitly defined by simple union types,
named by appending "Kind" to the name of their simple union type,
like in generated C.
- Types that don't occur in generated C. Their names start with ':'
so they don't clash with the user's names.
* All type references are by name.
* The struct and union types are generalized into an object type.
* Base types are flattened.
* Commands take a single argument and return a single result.
Dictionary argument or list result is an implicit type definition.
The empty object type is used when a command takes no arguments or
produces no results.
The argument is always of object type, but the introspection schema
doesn't reflect that.
The 'gen': false directive is omitted as implementation detail.
The 'success-response' directive is omitted as well for now, even
though it's not an implementation detail, because it's not used by
QMP.
* Events carry a single data value.
Implicit type definition and empty object type use, just like for
commands.
The value is of object type, but the introspection schema doesn't
reflect that.
* Types not used by commands or events are omitted.
Indirect use counts as use.
* Optional members have a default, which can only be null right now
Instead of a mandatory "optional" flag, we have an optional default.
No default means mandatory, default null means optional without
default value. Non-null is available for optional with default
(possible future extension).
* Clients should *not* look up types by name, because type names are
not ABI. Look up the command or event you're interested in, then
follow the references.
TODO Should we hide the type names to eliminate the temptation?
New generator scripts/qapi-introspect.py computes an introspection
value for its input, and generates a C variable holding it.
It can generate awfully long lines. Marked TODO.
A new test-qmp-input-visitor test case feeds its result for both
tests/qapi-schema/qapi-schema-test.json and qapi-schema.json to a
QmpInputVisitor to verify it actually conforms to the schema.
New QMP command query-qmp-schema takes its return value from that
variable. Its reply is some 85KiBytes for me right now.
If this turns out to be too much, we have a couple of options:
* We can use shorter names in the JSON. Not the QMP style.
* Optionally return the sub-schema for commands and events given as
arguments.
Right now qmp_query_schema() sends the string literal computed by
qmp-introspect.py. To compute sub-schema at run time, we'd have to
duplicate parts of qapi-introspect.py in C. Unattractive.
* Let clients cache the output of query-qmp-schema.
It changes only on QEMU upgrades, i.e. rarely. Provide a command
query-qmp-schema-hash. Clients can have a cache indexed by hash,
and re-query the schema only when they don't have it cached. Even
simpler: put the hash in the QMP greeting.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
2015-09-16 13:06:28 +02:00
|
|
|
|
|
|
|
Example: the SchemaInfo for ['str']
|
|
|
|
|
2015-11-06 07:35:35 +01:00
|
|
|
{ "name": "[str]", "meta-type": "array",
|
qapi: New QMP command query-qmp-schema for QMP introspection
qapi/introspect.json defines the introspection schema. It's designed
for QMP introspection, but should do for similar uses, such as QGA.
The introspection schema does not reflect all the rules and
restrictions that apply to QAPI schemata. A valid QAPI schema has an
introspection value conforming to the introspection schema, but the
converse is not true.
Introspection lowers away a number of schema details, and makes
implicit things explicit:
* The built-in types are declared with their JSON type.
All integer types are mapped to 'int', because how many bits we use
internally is an implementation detail. It could be pressed into
external interface service as very approximate range information,
but that's a bad idea. If we need range information, we better do
it properly.
* Implicit type definitions are made explicit, and given
auto-generated names:
- Array types, named by appending "List" to the name of their
element type, like in generated C.
- The enumeration types implicitly defined by simple union types,
named by appending "Kind" to the name of their simple union type,
like in generated C.
- Types that don't occur in generated C. Their names start with ':'
so they don't clash with the user's names.
* All type references are by name.
* The struct and union types are generalized into an object type.
* Base types are flattened.
* Commands take a single argument and return a single result.
Dictionary argument or list result is an implicit type definition.
The empty object type is used when a command takes no arguments or
produces no results.
The argument is always of object type, but the introspection schema
doesn't reflect that.
The 'gen': false directive is omitted as implementation detail.
The 'success-response' directive is omitted as well for now, even
though it's not an implementation detail, because it's not used by
QMP.
* Events carry a single data value.
Implicit type definition and empty object type use, just like for
commands.
The value is of object type, but the introspection schema doesn't
reflect that.
* Types not used by commands or events are omitted.
Indirect use counts as use.
* Optional members have a default, which can only be null right now
Instead of a mandatory "optional" flag, we have an optional default.
No default means mandatory, default null means optional without
default value. Non-null is available for optional with default
(possible future extension).
* Clients should *not* look up types by name, because type names are
not ABI. Look up the command or event you're interested in, then
follow the references.
TODO Should we hide the type names to eliminate the temptation?
New generator scripts/qapi-introspect.py computes an introspection
value for its input, and generates a C variable holding it.
It can generate awfully long lines. Marked TODO.
A new test-qmp-input-visitor test case feeds its result for both
tests/qapi-schema/qapi-schema-test.json and qapi-schema.json to a
QmpInputVisitor to verify it actually conforms to the schema.
New QMP command query-qmp-schema takes its return value from that
variable. Its reply is some 85KiBytes for me right now.
If this turns out to be too much, we have a couple of options:
* We can use shorter names in the JSON. Not the QMP style.
* Optionally return the sub-schema for commands and events given as
arguments.
Right now qmp_query_schema() sends the string literal computed by
qmp-introspect.py. To compute sub-schema at run time, we'd have to
duplicate parts of qapi-introspect.py in C. Unattractive.
* Let clients cache the output of query-qmp-schema.
It changes only on QEMU upgrades, i.e. rarely. Provide a command
query-qmp-schema-hash. Clients can have a cache indexed by hash,
and re-query the schema only when they don't have it cached. Even
simpler: put the hash in the QMP greeting.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
2015-09-16 13:06:28 +02:00
|
|
|
"element-type": "str" }
|
|
|
|
|
|
|
|
The SchemaInfo for an enumeration type has meta-type "enum" and
|
qapi-introspect: Document lack of sorting
qapi-code-gen.txt already claims that types, commands, and
events share a common namespace; set this in stone by further
documenting that our introspection output will never have
collisions with the same name tied to more than one meta-type.
Our largest QMP enum currently has 125 values, our largest
object type has 27 members, and the mean for each is less than
10. These sizes are small enough that the per-element overhead
of O(log n) binary searching probably outweighs the speed
possible with direct O(n) linear searching (a better algorithm
with more overhead will only beat a leaner naive algorithm only
as you scale to larger input sizes).
Arguably, the overall SchemaInfo array could be sorted by name;
there, we currently have 531 entities, large enough for a binary
search to be faster than linear. However, remember that we have
mutually-recursive types, which means there is no topological
ordering that will allow clients to learn all information about
that type in a single linear pass; thus clients will want to do
random access over the data, and they will probably read the
introspection output into a hashtable for O(1) lookup rather
than O(log n) binary searching, at which point, pre-sorting our
introspection output doesn't help the client.
It doesn't help that sorting can be subjective if you introduce
locales into the mix (I'm not experienced enough with Python
to know for sure, but at least it looks like it defaults to
sorting in the C locale even when run under a different locale).
And while our current introspection output is deterministic
(because we visit entities in a sorted order), we may want
to change that order in the future (such as using OrderedDict
to stick to .json declaration order).
For these reasons, we simply document that clients should not
rely on any particular order of items in introspection output.
And since it is now a documented part of the contract, we have
the freedom to later rearrange output if needed, without
worrying about breaking well-written clients.
Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1446791754-23823-13-git-send-email-eblake@redhat.com>
[Commit message tweaked]
Signed-off-by: Markus Armbruster <armbru@redhat.com>
2015-11-06 07:35:36 +01:00
|
|
|
variant member "values". The values are listed in no particular
|
|
|
|
order; clients must search the entire enum when learning whether a
|
|
|
|
particular value is supported.
|
qapi: New QMP command query-qmp-schema for QMP introspection
qapi/introspect.json defines the introspection schema. It's designed
for QMP introspection, but should do for similar uses, such as QGA.
The introspection schema does not reflect all the rules and
restrictions that apply to QAPI schemata. A valid QAPI schema has an
introspection value conforming to the introspection schema, but the
converse is not true.
Introspection lowers away a number of schema details, and makes
implicit things explicit:
* The built-in types are declared with their JSON type.
All integer types are mapped to 'int', because how many bits we use
internally is an implementation detail. It could be pressed into
external interface service as very approximate range information,
but that's a bad idea. If we need range information, we better do
it properly.
* Implicit type definitions are made explicit, and given
auto-generated names:
- Array types, named by appending "List" to the name of their
element type, like in generated C.
- The enumeration types implicitly defined by simple union types,
named by appending "Kind" to the name of their simple union type,
like in generated C.
- Types that don't occur in generated C. Their names start with ':'
so they don't clash with the user's names.
* All type references are by name.
* The struct and union types are generalized into an object type.
* Base types are flattened.
* Commands take a single argument and return a single result.
Dictionary argument or list result is an implicit type definition.
The empty object type is used when a command takes no arguments or
produces no results.
The argument is always of object type, but the introspection schema
doesn't reflect that.
The 'gen': false directive is omitted as implementation detail.
The 'success-response' directive is omitted as well for now, even
though it's not an implementation detail, because it's not used by
QMP.
* Events carry a single data value.
Implicit type definition and empty object type use, just like for
commands.
The value is of object type, but the introspection schema doesn't
reflect that.
* Types not used by commands or events are omitted.
Indirect use counts as use.
* Optional members have a default, which can only be null right now
Instead of a mandatory "optional" flag, we have an optional default.
No default means mandatory, default null means optional without
default value. Non-null is available for optional with default
(possible future extension).
* Clients should *not* look up types by name, because type names are
not ABI. Look up the command or event you're interested in, then
follow the references.
TODO Should we hide the type names to eliminate the temptation?
New generator scripts/qapi-introspect.py computes an introspection
value for its input, and generates a C variable holding it.
It can generate awfully long lines. Marked TODO.
A new test-qmp-input-visitor test case feeds its result for both
tests/qapi-schema/qapi-schema-test.json and qapi-schema.json to a
QmpInputVisitor to verify it actually conforms to the schema.
New QMP command query-qmp-schema takes its return value from that
variable. Its reply is some 85KiBytes for me right now.
If this turns out to be too much, we have a couple of options:
* We can use shorter names in the JSON. Not the QMP style.
* Optionally return the sub-schema for commands and events given as
arguments.
Right now qmp_query_schema() sends the string literal computed by
qmp-introspect.py. To compute sub-schema at run time, we'd have to
duplicate parts of qapi-introspect.py in C. Unattractive.
* Let clients cache the output of query-qmp-schema.
It changes only on QEMU upgrades, i.e. rarely. Provide a command
query-qmp-schema-hash. Clients can have a cache indexed by hash,
and re-query the schema only when they don't have it cached. Even
simpler: put the hash in the QMP greeting.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
2015-09-16 13:06:28 +02:00
|
|
|
|
|
|
|
Example: the SchemaInfo for MyEnum from section Enumeration types
|
|
|
|
|
|
|
|
{ "name": "MyEnum", "meta-type": "enum",
|
|
|
|
"values": [ "value1", "value2", "value3" ] }
|
|
|
|
|
|
|
|
The SchemaInfo for a built-in type has the same name as the type in
|
|
|
|
the QAPI schema (see section Built-in Types), with one exception
|
|
|
|
detailed below. It has variant member "json-type" that shows how
|
|
|
|
values of this type are encoded on the wire.
|
|
|
|
|
|
|
|
Example: the SchemaInfo for str
|
|
|
|
|
|
|
|
{ "name": "str", "meta-type": "builtin", "json-type": "string" }
|
|
|
|
|
|
|
|
The QAPI schema supports a number of integer types that only differ in
|
|
|
|
how they map to C. They are identical as far as SchemaInfo is
|
|
|
|
concerned. Therefore, they get all mapped to a single type "int" in
|
|
|
|
SchemaInfo.
|
|
|
|
|
|
|
|
As explained above, type names are not part of the wire ABI. Not even
|
|
|
|
the names of built-in types. Clients should examine member
|
|
|
|
"json-type" instead of hard-coding names of built-in types.
|
|
|
|
|
|
|
|
|
2011-07-19 21:50:46 +02:00
|
|
|
== Code generation ==
|
|
|
|
|
2016-03-03 17:16:46 +01:00
|
|
|
Schemas are fed into five scripts to generate all the code/files that,
|
qapi: New QMP command query-qmp-schema for QMP introspection
qapi/introspect.json defines the introspection schema. It's designed
for QMP introspection, but should do for similar uses, such as QGA.
The introspection schema does not reflect all the rules and
restrictions that apply to QAPI schemata. A valid QAPI schema has an
introspection value conforming to the introspection schema, but the
converse is not true.
Introspection lowers away a number of schema details, and makes
implicit things explicit:
* The built-in types are declared with their JSON type.
All integer types are mapped to 'int', because how many bits we use
internally is an implementation detail. It could be pressed into
external interface service as very approximate range information,
but that's a bad idea. If we need range information, we better do
it properly.
* Implicit type definitions are made explicit, and given
auto-generated names:
- Array types, named by appending "List" to the name of their
element type, like in generated C.
- The enumeration types implicitly defined by simple union types,
named by appending "Kind" to the name of their simple union type,
like in generated C.
- Types that don't occur in generated C. Their names start with ':'
so they don't clash with the user's names.
* All type references are by name.
* The struct and union types are generalized into an object type.
* Base types are flattened.
* Commands take a single argument and return a single result.
Dictionary argument or list result is an implicit type definition.
The empty object type is used when a command takes no arguments or
produces no results.
The argument is always of object type, but the introspection schema
doesn't reflect that.
The 'gen': false directive is omitted as implementation detail.
The 'success-response' directive is omitted as well for now, even
though it's not an implementation detail, because it's not used by
QMP.
* Events carry a single data value.
Implicit type definition and empty object type use, just like for
commands.
The value is of object type, but the introspection schema doesn't
reflect that.
* Types not used by commands or events are omitted.
Indirect use counts as use.
* Optional members have a default, which can only be null right now
Instead of a mandatory "optional" flag, we have an optional default.
No default means mandatory, default null means optional without
default value. Non-null is available for optional with default
(possible future extension).
* Clients should *not* look up types by name, because type names are
not ABI. Look up the command or event you're interested in, then
follow the references.
TODO Should we hide the type names to eliminate the temptation?
New generator scripts/qapi-introspect.py computes an introspection
value for its input, and generates a C variable holding it.
It can generate awfully long lines. Marked TODO.
A new test-qmp-input-visitor test case feeds its result for both
tests/qapi-schema/qapi-schema-test.json and qapi-schema.json to a
QmpInputVisitor to verify it actually conforms to the schema.
New QMP command query-qmp-schema takes its return value from that
variable. Its reply is some 85KiBytes for me right now.
If this turns out to be too much, we have a couple of options:
* We can use shorter names in the JSON. Not the QMP style.
* Optionally return the sub-schema for commands and events given as
arguments.
Right now qmp_query_schema() sends the string literal computed by
qmp-introspect.py. To compute sub-schema at run time, we'd have to
duplicate parts of qapi-introspect.py in C. Unattractive.
* Let clients cache the output of query-qmp-schema.
It changes only on QEMU upgrades, i.e. rarely. Provide a command
query-qmp-schema-hash. Clients can have a cache indexed by hash,
and re-query the schema only when they don't have it cached. Even
simpler: put the hash in the QMP greeting.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
2015-09-16 13:06:28 +02:00
|
|
|
paired with the core QAPI libraries, comprise everything required to
|
|
|
|
take JSON commands read in by a Client JSON Protocol server, unmarshal
|
|
|
|
the arguments into the underlying C types, call into the corresponding
|
2016-03-03 17:16:46 +01:00
|
|
|
C function, map the response back to a Client JSON Protocol response
|
|
|
|
to be returned to the user, and introspect the commands.
|
2011-07-19 21:50:46 +02:00
|
|
|
|
2016-03-03 17:16:46 +01:00
|
|
|
As an example, we'll use the following schema, which describes a
|
|
|
|
single complex user-defined type, along with command which takes a
|
|
|
|
list of that type as a parameter, and returns a single element of that
|
|
|
|
type. The user is responsible for writing the implementation of
|
|
|
|
qmp_my_command(); everything else is produced by the generator.
|
2011-07-19 21:50:46 +02:00
|
|
|
|
2014-05-14 17:27:23 +02:00
|
|
|
$ cat example-schema.json
|
2015-05-04 17:05:26 +02:00
|
|
|
{ 'struct': 'UserDefOne',
|
2016-03-03 17:16:46 +01:00
|
|
|
'data': { 'integer': 'int', '*string': 'str' } }
|
2011-07-19 21:50:46 +02:00
|
|
|
|
|
|
|
{ 'command': 'my-command',
|
2016-03-03 17:16:46 +01:00
|
|
|
'data': { 'arg1': ['UserDefOne'] },
|
2011-07-19 21:50:46 +02:00
|
|
|
'returns': 'UserDefOne' }
|
|
|
|
|
2014-09-26 17:20:33 +02:00
|
|
|
{ 'event': 'MY_EVENT' }
|
|
|
|
|
2016-03-03 17:16:46 +01:00
|
|
|
For a more thorough look at generated code, the testsuite includes
|
|
|
|
tests/qapi-schema/qapi-schema-tests.json that covers more examples of
|
|
|
|
what the generator will accept, and compiles the resulting C code as
|
|
|
|
part of 'make check-unit'.
|
|
|
|
|
2011-07-19 21:50:46 +02:00
|
|
|
=== scripts/qapi-types.py ===
|
|
|
|
|
2016-03-03 17:16:46 +01:00
|
|
|
Used to generate the C types defined by a schema, along with
|
|
|
|
supporting code. The following files are created:
|
2011-07-19 21:50:46 +02:00
|
|
|
|
|
|
|
$(prefix)qapi-types.h - C types corresponding to types defined in
|
|
|
|
the schema you pass in
|
|
|
|
$(prefix)qapi-types.c - Cleanup functions for the above C types
|
|
|
|
|
|
|
|
The $(prefix) is an optional parameter used as a namespace to keep the
|
|
|
|
generated code from one schema/code-generation separated from others so code
|
|
|
|
can be generated/used from multiple schemas without clobbering previously
|
|
|
|
created code.
|
|
|
|
|
|
|
|
Example:
|
|
|
|
|
2014-05-14 17:27:23 +02:00
|
|
|
$ python scripts/qapi-types.py --output-dir="qapi-generated" \
|
2015-04-02 13:32:16 +02:00
|
|
|
--prefix="example-" example-schema.json
|
2016-03-03 17:16:46 +01:00
|
|
|
$ cat qapi-generated/example-qapi-types.h
|
|
|
|
[Uninteresting stuff omitted...]
|
|
|
|
|
|
|
|
#ifndef EXAMPLE_QAPI_TYPES_H
|
|
|
|
#define EXAMPLE_QAPI_TYPES_H
|
|
|
|
|
|
|
|
[Built-in types omitted...]
|
|
|
|
|
|
|
|
typedef struct UserDefOne UserDefOne;
|
|
|
|
|
|
|
|
typedef struct UserDefOneList UserDefOneList;
|
|
|
|
|
|
|
|
struct UserDefOne {
|
|
|
|
int64_t integer;
|
|
|
|
bool has_string;
|
|
|
|
char *string;
|
|
|
|
};
|
|
|
|
|
|
|
|
void qapi_free_UserDefOne(UserDefOne *obj);
|
|
|
|
|
|
|
|
struct UserDefOneList {
|
|
|
|
UserDefOneList *next;
|
|
|
|
UserDefOne *value;
|
|
|
|
};
|
|
|
|
|
|
|
|
void qapi_free_UserDefOneList(UserDefOneList *obj);
|
|
|
|
|
|
|
|
#endif
|
2014-05-14 17:27:23 +02:00
|
|
|
$ cat qapi-generated/example-qapi-types.c
|
2014-05-07 09:53:43 +02:00
|
|
|
[Uninteresting stuff omitted...]
|
|
|
|
|
qapi-types: Convert to QAPISchemaVisitor, fixing flat unions
Fixes flat unions to get the base's base members. Test case is from
commit 2fc0043, in qapi-schema-test.json:
{ 'union': 'UserDefFlatUnion',
'base': 'UserDefUnionBase',
'discriminator': 'enum1',
'data': { 'value1' : 'UserDefA',
'value2' : 'UserDefB',
'value3' : 'UserDefB' } }
{ 'struct': 'UserDefUnionBase',
'base': 'UserDefZero',
'data': { 'string': 'str', 'enum1': 'EnumOne' } }
{ 'struct': 'UserDefZero',
'data': { 'integer': 'int' } }
Patch's effect on UserDefFlatUnion:
struct UserDefFlatUnion {
/* Members inherited from UserDefUnionBase: */
+ int64_t integer;
char *string;
EnumOne enum1;
/* Own members: */
union { /* union tag is @enum1 */
void *data;
UserDefA *value1;
UserDefB *value2;
UserDefB *value3;
};
};
Flat union visitors remain broken. They'll be fixed next.
Code is generated in a different order now, but that doesn't matter.
The two guards QAPI_TYPES_BUILTIN_STRUCT_DECL and
QAPI_TYPES_BUILTIN_CLEANUP_DECL are replaced by just
QAPI_TYPES_BUILTIN.
Two ugly special cases for simple unions now stand out like sore
thumbs:
1. The type tag is named 'type' everywhere, except in generated C,
where it's 'kind'.
2. QAPISchema lowers simple unions to semantically equivalent flat
unions. However, the C generated for a simple unions differs from
the C generated for its equivalent flat union, and we therefore
need special code to preserve that pointless difference for now.
Mark both TODO.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Daniel P. Berrange <berrange@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
2015-09-16 13:06:09 +02:00
|
|
|
void qapi_free_UserDefOne(UserDefOne *obj)
|
2014-05-07 09:53:43 +02:00
|
|
|
{
|
2015-09-30 00:21:09 +02:00
|
|
|
QapiDeallocVisitor *qdv;
|
2014-05-07 09:53:43 +02:00
|
|
|
Visitor *v;
|
|
|
|
|
|
|
|
if (!obj) {
|
|
|
|
return;
|
|
|
|
}
|
|
|
|
|
2015-09-30 00:21:09 +02:00
|
|
|
qdv = qapi_dealloc_visitor_new();
|
|
|
|
v = qapi_dealloc_get_visitor(qdv);
|
2016-03-03 17:16:46 +01:00
|
|
|
visit_type_UserDefOne(v, NULL, &obj, NULL);
|
2015-09-30 00:21:09 +02:00
|
|
|
qapi_dealloc_visitor_cleanup(qdv);
|
2014-05-07 09:53:43 +02:00
|
|
|
}
|
2011-07-19 21:50:46 +02:00
|
|
|
|
qapi-types: Convert to QAPISchemaVisitor, fixing flat unions
Fixes flat unions to get the base's base members. Test case is from
commit 2fc0043, in qapi-schema-test.json:
{ 'union': 'UserDefFlatUnion',
'base': 'UserDefUnionBase',
'discriminator': 'enum1',
'data': { 'value1' : 'UserDefA',
'value2' : 'UserDefB',
'value3' : 'UserDefB' } }
{ 'struct': 'UserDefUnionBase',
'base': 'UserDefZero',
'data': { 'string': 'str', 'enum1': 'EnumOne' } }
{ 'struct': 'UserDefZero',
'data': { 'integer': 'int' } }
Patch's effect on UserDefFlatUnion:
struct UserDefFlatUnion {
/* Members inherited from UserDefUnionBase: */
+ int64_t integer;
char *string;
EnumOne enum1;
/* Own members: */
union { /* union tag is @enum1 */
void *data;
UserDefA *value1;
UserDefB *value2;
UserDefB *value3;
};
};
Flat union visitors remain broken. They'll be fixed next.
Code is generated in a different order now, but that doesn't matter.
The two guards QAPI_TYPES_BUILTIN_STRUCT_DECL and
QAPI_TYPES_BUILTIN_CLEANUP_DECL are replaced by just
QAPI_TYPES_BUILTIN.
Two ugly special cases for simple unions now stand out like sore
thumbs:
1. The type tag is named 'type' everywhere, except in generated C,
where it's 'kind'.
2. QAPISchema lowers simple unions to semantically equivalent flat
unions. However, the C generated for a simple unions differs from
the C generated for its equivalent flat union, and we therefore
need special code to preserve that pointless difference for now.
Mark both TODO.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Daniel P. Berrange <berrange@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
2015-09-16 13:06:09 +02:00
|
|
|
void qapi_free_UserDefOneList(UserDefOneList *obj)
|
2011-07-19 21:50:46 +02:00
|
|
|
{
|
2015-09-30 00:21:09 +02:00
|
|
|
QapiDeallocVisitor *qdv;
|
2011-07-19 21:50:46 +02:00
|
|
|
Visitor *v;
|
|
|
|
|
|
|
|
if (!obj) {
|
|
|
|
return;
|
|
|
|
}
|
|
|
|
|
2015-09-30 00:21:09 +02:00
|
|
|
qdv = qapi_dealloc_visitor_new();
|
|
|
|
v = qapi_dealloc_get_visitor(qdv);
|
2016-03-03 17:16:46 +01:00
|
|
|
visit_type_UserDefOneList(v, NULL, &obj, NULL);
|
2015-09-30 00:21:09 +02:00
|
|
|
qapi_dealloc_visitor_cleanup(qdv);
|
2011-07-19 21:50:46 +02:00
|
|
|
}
|
|
|
|
|
|
|
|
=== scripts/qapi-visit.py ===
|
|
|
|
|
2016-03-03 17:16:46 +01:00
|
|
|
Used to generate the visitor functions used to walk through and
|
|
|
|
convert between a native QAPI C data structure and some other format
|
|
|
|
(such as QObject); the generated functions are named visit_type_FOO()
|
|
|
|
and visit_type_FOO_members().
|
2011-07-19 21:50:46 +02:00
|
|
|
|
|
|
|
The following files are generated:
|
|
|
|
|
|
|
|
$(prefix)qapi-visit.c: visitor function for a particular C type, used
|
|
|
|
to automagically convert QObjects into the
|
|
|
|
corresponding C type and vice-versa, as well
|
|
|
|
as for deallocating memory for an existing C
|
|
|
|
type
|
|
|
|
|
|
|
|
$(prefix)qapi-visit.h: declarations for previously mentioned visitor
|
|
|
|
functions
|
|
|
|
|
|
|
|
Example:
|
|
|
|
|
2014-05-14 17:27:23 +02:00
|
|
|
$ python scripts/qapi-visit.py --output-dir="qapi-generated"
|
2015-04-02 13:32:16 +02:00
|
|
|
--prefix="example-" example-schema.json
|
2016-03-03 17:16:46 +01:00
|
|
|
$ cat qapi-generated/example-qapi-visit.h
|
|
|
|
[Uninteresting stuff omitted...]
|
|
|
|
|
|
|
|
#ifndef EXAMPLE_QAPI_VISIT_H
|
|
|
|
#define EXAMPLE_QAPI_VISIT_H
|
|
|
|
|
|
|
|
[Visitors for built-in types omitted...]
|
|
|
|
|
|
|
|
void visit_type_UserDefOne_members(Visitor *v, UserDefOne *obj, Error **errp);
|
|
|
|
void visit_type_UserDefOne(Visitor *v, const char *name, UserDefOne **obj, Error **errp);
|
|
|
|
void visit_type_UserDefOneList(Visitor *v, const char *name, UserDefOneList **obj, Error **errp);
|
|
|
|
|
|
|
|
#endif
|
2014-05-14 17:27:23 +02:00
|
|
|
$ cat qapi-generated/example-qapi-visit.c
|
2014-05-07 09:53:43 +02:00
|
|
|
[Uninteresting stuff omitted...]
|
2011-07-19 21:50:46 +02:00
|
|
|
|
2016-03-03 17:16:46 +01:00
|
|
|
void visit_type_UserDefOne_members(Visitor *v, UserDefOne *obj, Error **errp)
|
2014-05-07 09:53:43 +02:00
|
|
|
{
|
|
|
|
Error *err = NULL;
|
2015-07-01 16:55:15 +02:00
|
|
|
|
2016-03-03 17:16:46 +01:00
|
|
|
visit_type_int(v, "integer", &obj->integer, &err);
|
qapi: Replace uncommon use of the error API by the common one
We commonly use the error API like this:
err = NULL;
foo(..., &err);
if (err) {
goto out;
}
bar(..., &err);
Every error source is checked separately. The second function is only
called when the first one succeeds. Both functions are free to pass
their argument to error_set(). Because error_set() asserts no error
has been set, this effectively means they must not be called with an
error set.
The qapi-generated code uses the error API differently:
// *errp was initialized to NULL somewhere up the call chain
frob(..., errp);
gnat(..., errp);
Errors accumulate in *errp: first error wins, subsequent errors get
dropped. To make this work, the second function does nothing when
called with an error set. Requires non-null errp, or else the second
function can't see the first one fail.
This usage has also bled into visitor tests, and two device model
object property getters rtc_get_date() and balloon_stats_get_all().
With the "accumulate" technique, you need fewer error checks in
callers, and buy that with an error check in every callee. Can be
nice.
However, mixing the two techniques is confusing. You can't use the
"accumulate" technique with functions designed for the "check
separately" technique. You can use the "check separately" technique
with functions designed for the "accumulate" technique, but then
error_set() can't catch you setting an error more than once.
Standardize on the "check separately" technique for now, because it's
overwhelmingly prevalent.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
2014-05-07 09:53:54 +02:00
|
|
|
if (err) {
|
|
|
|
goto out;
|
|
|
|
}
|
2016-03-03 17:16:46 +01:00
|
|
|
if (visit_optional(v, "string", &obj->has_string)) {
|
|
|
|
visit_type_str(v, "string", &obj->string, &err);
|
|
|
|
if (err) {
|
|
|
|
goto out;
|
|
|
|
}
|
qapi: Replace uncommon use of the error API by the common one
We commonly use the error API like this:
err = NULL;
foo(..., &err);
if (err) {
goto out;
}
bar(..., &err);
Every error source is checked separately. The second function is only
called when the first one succeeds. Both functions are free to pass
their argument to error_set(). Because error_set() asserts no error
has been set, this effectively means they must not be called with an
error set.
The qapi-generated code uses the error API differently:
// *errp was initialized to NULL somewhere up the call chain
frob(..., errp);
gnat(..., errp);
Errors accumulate in *errp: first error wins, subsequent errors get
dropped. To make this work, the second function does nothing when
called with an error set. Requires non-null errp, or else the second
function can't see the first one fail.
This usage has also bled into visitor tests, and two device model
object property getters rtc_get_date() and balloon_stats_get_all().
With the "accumulate" technique, you need fewer error checks in
callers, and buy that with an error check in every callee. Can be
nice.
However, mixing the two techniques is confusing. You can't use the
"accumulate" technique with functions designed for the "check
separately" technique. You can use the "check separately" technique
with functions designed for the "accumulate" technique, but then
error_set() can't catch you setting an error more than once.
Standardize on the "check separately" technique for now, because it's
overwhelmingly prevalent.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
2014-05-07 09:53:54 +02:00
|
|
|
}
|
2014-05-07 09:53:43 +02:00
|
|
|
|
qapi: Replace uncommon use of the error API by the common one
We commonly use the error API like this:
err = NULL;
foo(..., &err);
if (err) {
goto out;
}
bar(..., &err);
Every error source is checked separately. The second function is only
called when the first one succeeds. Both functions are free to pass
their argument to error_set(). Because error_set() asserts no error
has been set, this effectively means they must not be called with an
error set.
The qapi-generated code uses the error API differently:
// *errp was initialized to NULL somewhere up the call chain
frob(..., errp);
gnat(..., errp);
Errors accumulate in *errp: first error wins, subsequent errors get
dropped. To make this work, the second function does nothing when
called with an error set. Requires non-null errp, or else the second
function can't see the first one fail.
This usage has also bled into visitor tests, and two device model
object property getters rtc_get_date() and balloon_stats_get_all().
With the "accumulate" technique, you need fewer error checks in
callers, and buy that with an error check in every callee. Can be
nice.
However, mixing the two techniques is confusing. You can't use the
"accumulate" technique with functions designed for the "check
separately" technique. You can use the "check separately" technique
with functions designed for the "accumulate" technique, but then
error_set() can't catch you setting an error more than once.
Standardize on the "check separately" technique for now, because it's
overwhelmingly prevalent.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
2014-05-07 09:53:54 +02:00
|
|
|
out:
|
2014-05-07 09:53:43 +02:00
|
|
|
error_propagate(errp, err);
|
|
|
|
}
|
2011-07-19 21:50:46 +02:00
|
|
|
|
2016-03-03 17:16:46 +01:00
|
|
|
void visit_type_UserDefOne(Visitor *v, const char *name, UserDefOne **obj, Error **errp)
|
2011-07-19 21:50:46 +02:00
|
|
|
{
|
qapi: Replace uncommon use of the error API by the common one
We commonly use the error API like this:
err = NULL;
foo(..., &err);
if (err) {
goto out;
}
bar(..., &err);
Every error source is checked separately. The second function is only
called when the first one succeeds. Both functions are free to pass
their argument to error_set(). Because error_set() asserts no error
has been set, this effectively means they must not be called with an
error set.
The qapi-generated code uses the error API differently:
// *errp was initialized to NULL somewhere up the call chain
frob(..., errp);
gnat(..., errp);
Errors accumulate in *errp: first error wins, subsequent errors get
dropped. To make this work, the second function does nothing when
called with an error set. Requires non-null errp, or else the second
function can't see the first one fail.
This usage has also bled into visitor tests, and two device model
object property getters rtc_get_date() and balloon_stats_get_all().
With the "accumulate" technique, you need fewer error checks in
callers, and buy that with an error check in every callee. Can be
nice.
However, mixing the two techniques is confusing. You can't use the
"accumulate" technique with functions designed for the "check
separately" technique. You can use the "check separately" technique
with functions designed for the "accumulate" technique, but then
error_set() can't catch you setting an error more than once.
Standardize on the "check separately" technique for now, because it's
overwhelmingly prevalent.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
2014-05-07 09:53:54 +02:00
|
|
|
Error *err = NULL;
|
|
|
|
|
2016-03-03 17:16:46 +01:00
|
|
|
visit_start_struct(v, name, (void **)obj, sizeof(UserDefOne), &err);
|
|
|
|
if (err) {
|
|
|
|
goto out;
|
|
|
|
}
|
|
|
|
if (!*obj) {
|
|
|
|
goto out_obj;
|
2014-05-07 09:53:43 +02:00
|
|
|
}
|
2016-03-03 17:16:46 +01:00
|
|
|
visit_type_UserDefOne_members(v, *obj, &err);
|
qapi: Split visit_end_struct() into pieces
As mentioned in previous patches, we want to call visit_end_struct()
functions unconditionally, so that visitors can release resources
tied up since the matching visit_start_struct() without also having
to worry about error priority if more than one error occurs.
Even though error_propagate() can be safely used to ignore a second
error during cleanup caused by a first error, it is simpler if the
cleanup cannot set an error. So, split out the error checking
portion (basically, input visitors checking for unvisited keys) into
a new function visit_check_struct(), which can be safely skipped if
any earlier errors are encountered, and leave the cleanup portion
(which never fails, but must be called unconditionally if
visit_start_struct() succeeded) in visit_end_struct().
Generated code in qapi-visit.c has diffs resembling:
|@@ -59,10 +59,12 @@ void visit_type_ACPIOSTInfo(Visitor *v,
| goto out_obj;
| }
| visit_type_ACPIOSTInfo_members(v, obj, &err);
|- error_propagate(errp, err);
|- err = NULL;
|+ if (err) {
|+ goto out_obj;
|+ }
|+ visit_check_struct(v, &err);
| out_obj:
|- visit_end_struct(v, &err);
|+ visit_end_struct(v);
| out:
and in qapi-event.c:
@@ -47,7 +47,10 @@ void qapi_event_send_acpi_device_ost(ACP
| goto out;
| }
| visit_type_q_obj_ACPI_DEVICE_OST_arg_members(v, ¶m, &err);
|- visit_end_struct(v, err ? NULL : &err);
|+ if (!err) {
|+ visit_check_struct(v, &err);
|+ }
|+ visit_end_struct(v);
| if (err) {
| goto out;
Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1461879932-9020-20-git-send-email-eblake@redhat.com>
[Conflict with a doc fixup resolved]
Signed-off-by: Markus Armbruster <armbru@redhat.com>
2016-04-28 23:45:27 +02:00
|
|
|
if (err) {
|
|
|
|
goto out_obj;
|
|
|
|
}
|
|
|
|
visit_check_struct(v, &err);
|
2016-03-03 17:16:46 +01:00
|
|
|
out_obj:
|
qapi: Split visit_end_struct() into pieces
As mentioned in previous patches, we want to call visit_end_struct()
functions unconditionally, so that visitors can release resources
tied up since the matching visit_start_struct() without also having
to worry about error priority if more than one error occurs.
Even though error_propagate() can be safely used to ignore a second
error during cleanup caused by a first error, it is simpler if the
cleanup cannot set an error. So, split out the error checking
portion (basically, input visitors checking for unvisited keys) into
a new function visit_check_struct(), which can be safely skipped if
any earlier errors are encountered, and leave the cleanup portion
(which never fails, but must be called unconditionally if
visit_start_struct() succeeded) in visit_end_struct().
Generated code in qapi-visit.c has diffs resembling:
|@@ -59,10 +59,12 @@ void visit_type_ACPIOSTInfo(Visitor *v,
| goto out_obj;
| }
| visit_type_ACPIOSTInfo_members(v, obj, &err);
|- error_propagate(errp, err);
|- err = NULL;
|+ if (err) {
|+ goto out_obj;
|+ }
|+ visit_check_struct(v, &err);
| out_obj:
|- visit_end_struct(v, &err);
|+ visit_end_struct(v);
| out:
and in qapi-event.c:
@@ -47,7 +47,10 @@ void qapi_event_send_acpi_device_ost(ACP
| goto out;
| }
| visit_type_q_obj_ACPI_DEVICE_OST_arg_members(v, ¶m, &err);
|- visit_end_struct(v, err ? NULL : &err);
|+ if (!err) {
|+ visit_check_struct(v, &err);
|+ }
|+ visit_end_struct(v);
| if (err) {
| goto out;
Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1461879932-9020-20-git-send-email-eblake@redhat.com>
[Conflict with a doc fixup resolved]
Signed-off-by: Markus Armbruster <armbru@redhat.com>
2016-04-28 23:45:27 +02:00
|
|
|
visit_end_struct(v);
|
2016-03-03 17:16:46 +01:00
|
|
|
out:
|
qapi: Replace uncommon use of the error API by the common one
We commonly use the error API like this:
err = NULL;
foo(..., &err);
if (err) {
goto out;
}
bar(..., &err);
Every error source is checked separately. The second function is only
called when the first one succeeds. Both functions are free to pass
their argument to error_set(). Because error_set() asserts no error
has been set, this effectively means they must not be called with an
error set.
The qapi-generated code uses the error API differently:
// *errp was initialized to NULL somewhere up the call chain
frob(..., errp);
gnat(..., errp);
Errors accumulate in *errp: first error wins, subsequent errors get
dropped. To make this work, the second function does nothing when
called with an error set. Requires non-null errp, or else the second
function can't see the first one fail.
This usage has also bled into visitor tests, and two device model
object property getters rtc_get_date() and balloon_stats_get_all().
With the "accumulate" technique, you need fewer error checks in
callers, and buy that with an error check in every callee. Can be
nice.
However, mixing the two techniques is confusing. You can't use the
"accumulate" technique with functions designed for the "check
separately" technique. You can use the "check separately" technique
with functions designed for the "accumulate" technique, but then
error_set() can't catch you setting an error more than once.
Standardize on the "check separately" technique for now, because it's
overwhelmingly prevalent.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
2014-05-07 09:53:54 +02:00
|
|
|
error_propagate(errp, err);
|
2011-07-19 21:50:46 +02:00
|
|
|
}
|
|
|
|
|
2016-03-03 17:16:46 +01:00
|
|
|
void visit_type_UserDefOneList(Visitor *v, const char *name, UserDefOneList **obj, Error **errp)
|
2011-07-19 21:50:46 +02:00
|
|
|
{
|
2014-05-07 09:53:43 +02:00
|
|
|
Error *err = NULL;
|
qapi: Simplify semantics of visit_next_list()
The semantics of the list visit are somewhat baroque, with the
following pseudocode when FooList is used:
start()
for (prev = head; cur = next(prev); prev = &cur) {
visit(&cur->value)
}
Note that these semantics (advance before visit) requires that
the first call to next() return the list head, while all other
calls return the next element of the list; that is, every visitor
implementation is required to track extra state to decide whether
to return the input as-is, or to advance. It also requires an
argument of 'GenericList **' to next(), solely because the first
iteration might need to modify the caller's GenericList head, so
that all other calls have to do a layer of dereferencing.
Thankfully, we only have two uses of list visits in the entire
code base: one in spapr_drc (which completely avoids
visit_next_list(), feeding in integers from a different source
than uint8List), and one in qapi-visit.py. That is, all other
list visitors are generated in qapi-visit.c, and share the same
paradigm based on a qapi FooList type, so we can refactor how
lists are laid out with minimal churn among clients.
We can greatly simplify things by hoisting the special case
into the start() routine, and flipping the order in the loop
to visit before advance:
start(head)
for (tail = *head; tail; tail = next(tail)) {
visit(&tail->value)
}
With the simpler semantics, visitors have less state to track,
the argument to next() is reduced to 'GenericList *', and it
also becomes obvious whether an input visitor is allocating a
FooList during visit_start_list() (rather than the old way of
not knowing if an allocation happened until the first
visit_next_list()). As a minor drawback, we now allocate in
two functions instead of one, and have to pass the size to
both functions (unless we were to tweak the input visitors to
cache the size to start_list for reuse during next_list, but
that defeats the goal of less visitor state).
The signature of visit_start_list() is chosen to match
visit_start_struct(), with the new parameters after 'name'.
The spapr_drc case is a virtual visit, done by passing NULL for
list, similarly to how NULL is passed to visit_start_struct()
when a qapi type is not used in those visits. It was easy to
provide these semantics for qmp-output and dealloc visitors,
and a bit harder for qmp-input (several prerequisite patches
refactored things to make this patch straightforward). But it
turned out that the string and opts visitors munge enough other
state during visit_next_list() to make it easier to just
document and require a GenericList visit for now; an assertion
will remind us to adjust things if we need the semantics in the
future.
Several pre-requisite cleanup patches made the reshuffling of
the various visitors easier; particularly the qmp input visitor.
Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1461879932-9020-24-git-send-email-eblake@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
2016-04-28 23:45:31 +02:00
|
|
|
UserDefOneList *tail;
|
|
|
|
size_t size = sizeof(**obj);
|
2014-05-07 09:53:43 +02:00
|
|
|
|
qapi: Simplify semantics of visit_next_list()
The semantics of the list visit are somewhat baroque, with the
following pseudocode when FooList is used:
start()
for (prev = head; cur = next(prev); prev = &cur) {
visit(&cur->value)
}
Note that these semantics (advance before visit) requires that
the first call to next() return the list head, while all other
calls return the next element of the list; that is, every visitor
implementation is required to track extra state to decide whether
to return the input as-is, or to advance. It also requires an
argument of 'GenericList **' to next(), solely because the first
iteration might need to modify the caller's GenericList head, so
that all other calls have to do a layer of dereferencing.
Thankfully, we only have two uses of list visits in the entire
code base: one in spapr_drc (which completely avoids
visit_next_list(), feeding in integers from a different source
than uint8List), and one in qapi-visit.py. That is, all other
list visitors are generated in qapi-visit.c, and share the same
paradigm based on a qapi FooList type, so we can refactor how
lists are laid out with minimal churn among clients.
We can greatly simplify things by hoisting the special case
into the start() routine, and flipping the order in the loop
to visit before advance:
start(head)
for (tail = *head; tail; tail = next(tail)) {
visit(&tail->value)
}
With the simpler semantics, visitors have less state to track,
the argument to next() is reduced to 'GenericList *', and it
also becomes obvious whether an input visitor is allocating a
FooList during visit_start_list() (rather than the old way of
not knowing if an allocation happened until the first
visit_next_list()). As a minor drawback, we now allocate in
two functions instead of one, and have to pass the size to
both functions (unless we were to tweak the input visitors to
cache the size to start_list for reuse during next_list, but
that defeats the goal of less visitor state).
The signature of visit_start_list() is chosen to match
visit_start_struct(), with the new parameters after 'name'.
The spapr_drc case is a virtual visit, done by passing NULL for
list, similarly to how NULL is passed to visit_start_struct()
when a qapi type is not used in those visits. It was easy to
provide these semantics for qmp-output and dealloc visitors,
and a bit harder for qmp-input (several prerequisite patches
refactored things to make this patch straightforward). But it
turned out that the string and opts visitors munge enough other
state during visit_next_list() to make it easier to just
document and require a GenericList visit for now; an assertion
will remind us to adjust things if we need the semantics in the
future.
Several pre-requisite cleanup patches made the reshuffling of
the various visitors easier; particularly the qmp input visitor.
Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1461879932-9020-24-git-send-email-eblake@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
2016-04-28 23:45:31 +02:00
|
|
|
visit_start_list(v, name, (GenericList **)obj, size, &err);
|
qapi: Replace uncommon use of the error API by the common one
We commonly use the error API like this:
err = NULL;
foo(..., &err);
if (err) {
goto out;
}
bar(..., &err);
Every error source is checked separately. The second function is only
called when the first one succeeds. Both functions are free to pass
their argument to error_set(). Because error_set() asserts no error
has been set, this effectively means they must not be called with an
error set.
The qapi-generated code uses the error API differently:
// *errp was initialized to NULL somewhere up the call chain
frob(..., errp);
gnat(..., errp);
Errors accumulate in *errp: first error wins, subsequent errors get
dropped. To make this work, the second function does nothing when
called with an error set. Requires non-null errp, or else the second
function can't see the first one fail.
This usage has also bled into visitor tests, and two device model
object property getters rtc_get_date() and balloon_stats_get_all().
With the "accumulate" technique, you need fewer error checks in
callers, and buy that with an error check in every callee. Can be
nice.
However, mixing the two techniques is confusing. You can't use the
"accumulate" technique with functions designed for the "check
separately" technique. You can use the "check separately" technique
with functions designed for the "accumulate" technique, but then
error_set() can't catch you setting an error more than once.
Standardize on the "check separately" technique for now, because it's
overwhelmingly prevalent.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
2014-05-07 09:53:54 +02:00
|
|
|
if (err) {
|
|
|
|
goto out;
|
|
|
|
}
|
|
|
|
|
qapi: Simplify semantics of visit_next_list()
The semantics of the list visit are somewhat baroque, with the
following pseudocode when FooList is used:
start()
for (prev = head; cur = next(prev); prev = &cur) {
visit(&cur->value)
}
Note that these semantics (advance before visit) requires that
the first call to next() return the list head, while all other
calls return the next element of the list; that is, every visitor
implementation is required to track extra state to decide whether
to return the input as-is, or to advance. It also requires an
argument of 'GenericList **' to next(), solely because the first
iteration might need to modify the caller's GenericList head, so
that all other calls have to do a layer of dereferencing.
Thankfully, we only have two uses of list visits in the entire
code base: one in spapr_drc (which completely avoids
visit_next_list(), feeding in integers from a different source
than uint8List), and one in qapi-visit.py. That is, all other
list visitors are generated in qapi-visit.c, and share the same
paradigm based on a qapi FooList type, so we can refactor how
lists are laid out with minimal churn among clients.
We can greatly simplify things by hoisting the special case
into the start() routine, and flipping the order in the loop
to visit before advance:
start(head)
for (tail = *head; tail; tail = next(tail)) {
visit(&tail->value)
}
With the simpler semantics, visitors have less state to track,
the argument to next() is reduced to 'GenericList *', and it
also becomes obvious whether an input visitor is allocating a
FooList during visit_start_list() (rather than the old way of
not knowing if an allocation happened until the first
visit_next_list()). As a minor drawback, we now allocate in
two functions instead of one, and have to pass the size to
both functions (unless we were to tweak the input visitors to
cache the size to start_list for reuse during next_list, but
that defeats the goal of less visitor state).
The signature of visit_start_list() is chosen to match
visit_start_struct(), with the new parameters after 'name'.
The spapr_drc case is a virtual visit, done by passing NULL for
list, similarly to how NULL is passed to visit_start_struct()
when a qapi type is not used in those visits. It was easy to
provide these semantics for qmp-output and dealloc visitors,
and a bit harder for qmp-input (several prerequisite patches
refactored things to make this patch straightforward). But it
turned out that the string and opts visitors munge enough other
state during visit_next_list() to make it easier to just
document and require a GenericList visit for now; an assertion
will remind us to adjust things if we need the semantics in the
future.
Several pre-requisite cleanup patches made the reshuffling of
the various visitors easier; particularly the qmp input visitor.
Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1461879932-9020-24-git-send-email-eblake@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
2016-04-28 23:45:31 +02:00
|
|
|
for (tail = *obj; tail;
|
|
|
|
tail = (UserDefOneList *)visit_next_list(v, (GenericList *)tail, size)) {
|
|
|
|
visit_type_UserDefOne(v, NULL, &tail->value, &err);
|
|
|
|
if (err) {
|
|
|
|
break;
|
|
|
|
}
|
2011-07-19 21:50:46 +02:00
|
|
|
}
|
qapi: Replace uncommon use of the error API by the common one
We commonly use the error API like this:
err = NULL;
foo(..., &err);
if (err) {
goto out;
}
bar(..., &err);
Every error source is checked separately. The second function is only
called when the first one succeeds. Both functions are free to pass
their argument to error_set(). Because error_set() asserts no error
has been set, this effectively means they must not be called with an
error set.
The qapi-generated code uses the error API differently:
// *errp was initialized to NULL somewhere up the call chain
frob(..., errp);
gnat(..., errp);
Errors accumulate in *errp: first error wins, subsequent errors get
dropped. To make this work, the second function does nothing when
called with an error set. Requires non-null errp, or else the second
function can't see the first one fail.
This usage has also bled into visitor tests, and two device model
object property getters rtc_get_date() and balloon_stats_get_all().
With the "accumulate" technique, you need fewer error checks in
callers, and buy that with an error check in every callee. Can be
nice.
However, mixing the two techniques is confusing. You can't use the
"accumulate" technique with functions designed for the "check
separately" technique. You can use the "check separately" technique
with functions designed for the "accumulate" technique, but then
error_set() can't catch you setting an error more than once.
Standardize on the "check separately" technique for now, because it's
overwhelmingly prevalent.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
2014-05-07 09:53:54 +02:00
|
|
|
|
2016-03-03 17:16:46 +01:00
|
|
|
visit_end_list(v);
|
qapi: Replace uncommon use of the error API by the common one
We commonly use the error API like this:
err = NULL;
foo(..., &err);
if (err) {
goto out;
}
bar(..., &err);
Every error source is checked separately. The second function is only
called when the first one succeeds. Both functions are free to pass
their argument to error_set(). Because error_set() asserts no error
has been set, this effectively means they must not be called with an
error set.
The qapi-generated code uses the error API differently:
// *errp was initialized to NULL somewhere up the call chain
frob(..., errp);
gnat(..., errp);
Errors accumulate in *errp: first error wins, subsequent errors get
dropped. To make this work, the second function does nothing when
called with an error set. Requires non-null errp, or else the second
function can't see the first one fail.
This usage has also bled into visitor tests, and two device model
object property getters rtc_get_date() and balloon_stats_get_all().
With the "accumulate" technique, you need fewer error checks in
callers, and buy that with an error check in every callee. Can be
nice.
However, mixing the two techniques is confusing. You can't use the
"accumulate" technique with functions designed for the "check
separately" technique. You can use the "check separately" technique
with functions designed for the "accumulate" technique, but then
error_set() can't catch you setting an error more than once.
Standardize on the "check separately" technique for now, because it's
overwhelmingly prevalent.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
2014-05-07 09:53:54 +02:00
|
|
|
out:
|
|
|
|
error_propagate(errp, err);
|
2011-07-19 21:50:46 +02:00
|
|
|
}
|
|
|
|
|
|
|
|
=== scripts/qapi-commands.py ===
|
|
|
|
|
2016-03-03 17:16:46 +01:00
|
|
|
Used to generate the marshaling/dispatch functions for the commands
|
|
|
|
defined in the schema. The generated code implements
|
|
|
|
qmp_marshal_COMMAND() (mentioned in qmp-commands.hx, and registered
|
|
|
|
automatically), and declares qmp_COMMAND() that the user must
|
|
|
|
implement. The following files are generated:
|
2011-07-19 21:50:46 +02:00
|
|
|
|
|
|
|
$(prefix)qmp-marshal.c: command marshal/dispatch functions for each
|
|
|
|
QMP command defined in the schema. Functions
|
|
|
|
generated by qapi-visit.py are used to
|
2011-08-28 21:45:40 +02:00
|
|
|
convert QObjects received from the wire into
|
2011-07-19 21:50:46 +02:00
|
|
|
function parameters, and uses the same
|
|
|
|
visitor functions to convert native C return
|
|
|
|
values to QObjects from transmission back
|
|
|
|
over the wire.
|
|
|
|
|
|
|
|
$(prefix)qmp-commands.h: Function prototypes for the QMP commands
|
|
|
|
specified in the schema.
|
|
|
|
|
|
|
|
Example:
|
|
|
|
|
2014-09-26 17:20:33 +02:00
|
|
|
$ python scripts/qapi-commands.py --output-dir="qapi-generated"
|
2015-04-02 13:32:16 +02:00
|
|
|
--prefix="example-" example-schema.json
|
2016-03-03 17:16:46 +01:00
|
|
|
$ cat qapi-generated/example-qmp-commands.h
|
|
|
|
[Uninteresting stuff omitted...]
|
|
|
|
|
|
|
|
#ifndef EXAMPLE_QMP_COMMANDS_H
|
|
|
|
#define EXAMPLE_QMP_COMMANDS_H
|
|
|
|
|
|
|
|
#include "example-qapi-types.h"
|
|
|
|
#include "qapi/qmp/qdict.h"
|
|
|
|
#include "qapi/error.h"
|
|
|
|
|
|
|
|
UserDefOne *qmp_my_command(UserDefOneList *arg1, Error **errp);
|
|
|
|
|
|
|
|
#endif
|
2014-05-14 17:27:23 +02:00
|
|
|
$ cat qapi-generated/example-qmp-marshal.c
|
2014-05-07 09:53:43 +02:00
|
|
|
[Uninteresting stuff omitted...]
|
2011-07-19 21:50:46 +02:00
|
|
|
|
2015-09-16 13:06:21 +02:00
|
|
|
static void qmp_marshal_output_UserDefOne(UserDefOne *ret_in, QObject **ret_out, Error **errp)
|
2011-07-19 21:50:46 +02:00
|
|
|
{
|
2015-09-30 00:21:08 +02:00
|
|
|
Error *err = NULL;
|
2015-09-30 00:21:09 +02:00
|
|
|
QmpOutputVisitor *qov = qmp_output_visitor_new();
|
|
|
|
QapiDeallocVisitor *qdv;
|
2011-07-19 21:50:46 +02:00
|
|
|
Visitor *v;
|
|
|
|
|
2015-09-30 00:21:09 +02:00
|
|
|
v = qmp_output_get_visitor(qov);
|
2016-03-03 17:16:46 +01:00
|
|
|
visit_type_UserDefOne(v, "unused", &ret_in, &err);
|
2015-09-30 00:21:08 +02:00
|
|
|
if (err) {
|
qapi: Replace uncommon use of the error API by the common one
We commonly use the error API like this:
err = NULL;
foo(..., &err);
if (err) {
goto out;
}
bar(..., &err);
Every error source is checked separately. The second function is only
called when the first one succeeds. Both functions are free to pass
their argument to error_set(). Because error_set() asserts no error
has been set, this effectively means they must not be called with an
error set.
The qapi-generated code uses the error API differently:
// *errp was initialized to NULL somewhere up the call chain
frob(..., errp);
gnat(..., errp);
Errors accumulate in *errp: first error wins, subsequent errors get
dropped. To make this work, the second function does nothing when
called with an error set. Requires non-null errp, or else the second
function can't see the first one fail.
This usage has also bled into visitor tests, and two device model
object property getters rtc_get_date() and balloon_stats_get_all().
With the "accumulate" technique, you need fewer error checks in
callers, and buy that with an error check in every callee. Can be
nice.
However, mixing the two techniques is confusing. You can't use the
"accumulate" technique with functions designed for the "check
separately" technique. You can use the "check separately" technique
with functions designed for the "accumulate" technique, but then
error_set() can't catch you setting an error more than once.
Standardize on the "check separately" technique for now, because it's
overwhelmingly prevalent.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
2014-05-07 09:53:54 +02:00
|
|
|
goto out;
|
2014-05-07 09:53:43 +02:00
|
|
|
}
|
2015-09-30 00:21:09 +02:00
|
|
|
*ret_out = qmp_output_get_qobject(qov);
|
qapi: Replace uncommon use of the error API by the common one
We commonly use the error API like this:
err = NULL;
foo(..., &err);
if (err) {
goto out;
}
bar(..., &err);
Every error source is checked separately. The second function is only
called when the first one succeeds. Both functions are free to pass
their argument to error_set(). Because error_set() asserts no error
has been set, this effectively means they must not be called with an
error set.
The qapi-generated code uses the error API differently:
// *errp was initialized to NULL somewhere up the call chain
frob(..., errp);
gnat(..., errp);
Errors accumulate in *errp: first error wins, subsequent errors get
dropped. To make this work, the second function does nothing when
called with an error set. Requires non-null errp, or else the second
function can't see the first one fail.
This usage has also bled into visitor tests, and two device model
object property getters rtc_get_date() and balloon_stats_get_all().
With the "accumulate" technique, you need fewer error checks in
callers, and buy that with an error check in every callee. Can be
nice.
However, mixing the two techniques is confusing. You can't use the
"accumulate" technique with functions designed for the "check
separately" technique. You can use the "check separately" technique
with functions designed for the "accumulate" technique, but then
error_set() can't catch you setting an error more than once.
Standardize on the "check separately" technique for now, because it's
overwhelmingly prevalent.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
2014-05-07 09:53:54 +02:00
|
|
|
|
|
|
|
out:
|
2015-09-30 00:21:08 +02:00
|
|
|
error_propagate(errp, err);
|
2015-09-30 00:21:09 +02:00
|
|
|
qmp_output_visitor_cleanup(qov);
|
|
|
|
qdv = qapi_dealloc_visitor_new();
|
|
|
|
v = qapi_dealloc_get_visitor(qdv);
|
2016-03-03 17:16:46 +01:00
|
|
|
visit_type_UserDefOne(v, "unused", &ret_in, NULL);
|
2015-09-30 00:21:09 +02:00
|
|
|
qapi_dealloc_visitor_cleanup(qdv);
|
2011-07-19 21:50:46 +02:00
|
|
|
}
|
|
|
|
|
2015-09-16 13:06:19 +02:00
|
|
|
static void qmp_marshal_my_command(QDict *args, QObject **ret, Error **errp)
|
2011-07-19 21:50:46 +02:00
|
|
|
{
|
2015-09-30 00:21:08 +02:00
|
|
|
Error *err = NULL;
|
2015-07-31 18:51:18 +02:00
|
|
|
UserDefOne *retval;
|
2016-04-28 23:45:13 +02:00
|
|
|
QmpInputVisitor *qiv = qmp_input_visitor_new(QOBJECT(args), true);
|
2015-09-30 00:21:09 +02:00
|
|
|
QapiDeallocVisitor *qdv;
|
2011-07-19 21:50:46 +02:00
|
|
|
Visitor *v;
|
2016-03-03 17:16:46 +01:00
|
|
|
UserDefOneList *arg1 = NULL;
|
2011-07-19 21:50:46 +02:00
|
|
|
|
2015-09-30 00:21:09 +02:00
|
|
|
v = qmp_input_get_visitor(qiv);
|
qapi-commands: Wrap argument visit in visit_start_struct
The qmp-input visitor was allowing callers to play rather fast
and loose: when visiting a QDict, you could grab members of the
root dictionary without first pushing into the dict; among the
culprit callers was the generated marshal code on the 'arguments'
dictionary of a QMP command. But we are about to tighten the
input visitor, at which point the generated marshal code MUST
follow the same paradigms as everyone else, of pushing into the
struct before grabbing its keys.
Generated code grows as follows:
|@@ -515,7 +641,12 @@ void qmp_marshal_blockdev_backup(QDict *
| BlockdevBackup arg = {0};
|
| v = qmp_input_get_visitor(qiv);
|+ visit_start_struct(v, NULL, NULL, 0, &err);
|+ if (err) {
|+ goto out;
|+ }
| visit_type_BlockdevBackup_members(v, &arg, &err);
|+ visit_end_struct(v, err ? NULL : &err);
| if (err) {
| goto out;
| }
|@@ -527,7 +715,9 @@ out:
| qmp_input_visitor_cleanup(qiv);
| qdv = qapi_dealloc_visitor_new();
| v = qapi_dealloc_get_visitor(qdv);
|+ visit_start_struct(v, NULL, NULL, 0, NULL);
| visit_type_BlockdevBackup_members(v, &arg, NULL);
|+ visit_end_struct(v, NULL);
| qapi_dealloc_visitor_cleanup(qdv);
| }
The use of 'err ? NULL : &err' is temporary; a later patch will
clean that up when it splits visit_end_struct().
Prior to this patch, the fact that there was no final
visit_end_struct() meant that even though we are using a strict
input visit, the marshalling code was not detecting excess input
at the top level (only in nested levels). Fortunately, we have
code in monitor.c:qmp_check_client_args() that also checks for
no excess arguments at the top level. But as the generated code
is more compact than the manual check, a later patch will clean
up monitor.c to drop the redundancy added here.
Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1461879932-9020-9-git-send-email-eblake@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
2016-04-28 23:45:16 +02:00
|
|
|
visit_start_struct(v, NULL, NULL, 0, &err);
|
|
|
|
if (err) {
|
|
|
|
goto out;
|
|
|
|
}
|
2016-03-03 17:16:46 +01:00
|
|
|
visit_type_UserDefOneList(v, "arg1", &arg1, &err);
|
qapi: Split visit_end_struct() into pieces
As mentioned in previous patches, we want to call visit_end_struct()
functions unconditionally, so that visitors can release resources
tied up since the matching visit_start_struct() without also having
to worry about error priority if more than one error occurs.
Even though error_propagate() can be safely used to ignore a second
error during cleanup caused by a first error, it is simpler if the
cleanup cannot set an error. So, split out the error checking
portion (basically, input visitors checking for unvisited keys) into
a new function visit_check_struct(), which can be safely skipped if
any earlier errors are encountered, and leave the cleanup portion
(which never fails, but must be called unconditionally if
visit_start_struct() succeeded) in visit_end_struct().
Generated code in qapi-visit.c has diffs resembling:
|@@ -59,10 +59,12 @@ void visit_type_ACPIOSTInfo(Visitor *v,
| goto out_obj;
| }
| visit_type_ACPIOSTInfo_members(v, obj, &err);
|- error_propagate(errp, err);
|- err = NULL;
|+ if (err) {
|+ goto out_obj;
|+ }
|+ visit_check_struct(v, &err);
| out_obj:
|- visit_end_struct(v, &err);
|+ visit_end_struct(v);
| out:
and in qapi-event.c:
@@ -47,7 +47,10 @@ void qapi_event_send_acpi_device_ost(ACP
| goto out;
| }
| visit_type_q_obj_ACPI_DEVICE_OST_arg_members(v, ¶m, &err);
|- visit_end_struct(v, err ? NULL : &err);
|+ if (!err) {
|+ visit_check_struct(v, &err);
|+ }
|+ visit_end_struct(v);
| if (err) {
| goto out;
Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1461879932-9020-20-git-send-email-eblake@redhat.com>
[Conflict with a doc fixup resolved]
Signed-off-by: Markus Armbruster <armbru@redhat.com>
2016-04-28 23:45:27 +02:00
|
|
|
if (!err) {
|
|
|
|
visit_check_struct(v, &err);
|
|
|
|
}
|
|
|
|
visit_end_struct(v);
|
2015-09-30 00:21:08 +02:00
|
|
|
if (err) {
|
2011-07-19 21:50:46 +02:00
|
|
|
goto out;
|
|
|
|
}
|
qapi: Replace uncommon use of the error API by the common one
We commonly use the error API like this:
err = NULL;
foo(..., &err);
if (err) {
goto out;
}
bar(..., &err);
Every error source is checked separately. The second function is only
called when the first one succeeds. Both functions are free to pass
their argument to error_set(). Because error_set() asserts no error
has been set, this effectively means they must not be called with an
error set.
The qapi-generated code uses the error API differently:
// *errp was initialized to NULL somewhere up the call chain
frob(..., errp);
gnat(..., errp);
Errors accumulate in *errp: first error wins, subsequent errors get
dropped. To make this work, the second function does nothing when
called with an error set. Requires non-null errp, or else the second
function can't see the first one fail.
This usage has also bled into visitor tests, and two device model
object property getters rtc_get_date() and balloon_stats_get_all().
With the "accumulate" technique, you need fewer error checks in
callers, and buy that with an error check in every callee. Can be
nice.
However, mixing the two techniques is confusing. You can't use the
"accumulate" technique with functions designed for the "check
separately" technique. You can use the "check separately" technique
with functions designed for the "accumulate" technique, but then
error_set() can't catch you setting an error more than once.
Standardize on the "check separately" technique for now, because it's
overwhelmingly prevalent.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
2014-05-07 09:53:54 +02:00
|
|
|
|
2015-09-30 00:21:08 +02:00
|
|
|
retval = qmp_my_command(arg1, &err);
|
|
|
|
if (err) {
|
qapi: Replace uncommon use of the error API by the common one
We commonly use the error API like this:
err = NULL;
foo(..., &err);
if (err) {
goto out;
}
bar(..., &err);
Every error source is checked separately. The second function is only
called when the first one succeeds. Both functions are free to pass
their argument to error_set(). Because error_set() asserts no error
has been set, this effectively means they must not be called with an
error set.
The qapi-generated code uses the error API differently:
// *errp was initialized to NULL somewhere up the call chain
frob(..., errp);
gnat(..., errp);
Errors accumulate in *errp: first error wins, subsequent errors get
dropped. To make this work, the second function does nothing when
called with an error set. Requires non-null errp, or else the second
function can't see the first one fail.
This usage has also bled into visitor tests, and two device model
object property getters rtc_get_date() and balloon_stats_get_all().
With the "accumulate" technique, you need fewer error checks in
callers, and buy that with an error check in every callee. Can be
nice.
However, mixing the two techniques is confusing. You can't use the
"accumulate" technique with functions designed for the "check
separately" technique. You can use the "check separately" technique
with functions designed for the "accumulate" technique, but then
error_set() can't catch you setting an error more than once.
Standardize on the "check separately" technique for now, because it's
overwhelmingly prevalent.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
2014-05-07 09:53:54 +02:00
|
|
|
goto out;
|
2014-05-07 09:53:43 +02:00
|
|
|
}
|
2011-07-19 21:50:46 +02:00
|
|
|
|
2015-09-30 00:21:08 +02:00
|
|
|
qmp_marshal_output_UserDefOne(retval, ret, &err);
|
qapi: Replace uncommon use of the error API by the common one
We commonly use the error API like this:
err = NULL;
foo(..., &err);
if (err) {
goto out;
}
bar(..., &err);
Every error source is checked separately. The second function is only
called when the first one succeeds. Both functions are free to pass
their argument to error_set(). Because error_set() asserts no error
has been set, this effectively means they must not be called with an
error set.
The qapi-generated code uses the error API differently:
// *errp was initialized to NULL somewhere up the call chain
frob(..., errp);
gnat(..., errp);
Errors accumulate in *errp: first error wins, subsequent errors get
dropped. To make this work, the second function does nothing when
called with an error set. Requires non-null errp, or else the second
function can't see the first one fail.
This usage has also bled into visitor tests, and two device model
object property getters rtc_get_date() and balloon_stats_get_all().
With the "accumulate" technique, you need fewer error checks in
callers, and buy that with an error check in every callee. Can be
nice.
However, mixing the two techniques is confusing. You can't use the
"accumulate" technique with functions designed for the "check
separately" technique. You can use the "check separately" technique
with functions designed for the "accumulate" technique, but then
error_set() can't catch you setting an error more than once.
Standardize on the "check separately" technique for now, because it's
overwhelmingly prevalent.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
2014-05-07 09:53:54 +02:00
|
|
|
|
2011-07-19 21:50:46 +02:00
|
|
|
out:
|
2015-09-30 00:21:08 +02:00
|
|
|
error_propagate(errp, err);
|
2015-09-30 00:21:09 +02:00
|
|
|
qmp_input_visitor_cleanup(qiv);
|
|
|
|
qdv = qapi_dealloc_visitor_new();
|
|
|
|
v = qapi_dealloc_get_visitor(qdv);
|
qapi-commands: Wrap argument visit in visit_start_struct
The qmp-input visitor was allowing callers to play rather fast
and loose: when visiting a QDict, you could grab members of the
root dictionary without first pushing into the dict; among the
culprit callers was the generated marshal code on the 'arguments'
dictionary of a QMP command. But we are about to tighten the
input visitor, at which point the generated marshal code MUST
follow the same paradigms as everyone else, of pushing into the
struct before grabbing its keys.
Generated code grows as follows:
|@@ -515,7 +641,12 @@ void qmp_marshal_blockdev_backup(QDict *
| BlockdevBackup arg = {0};
|
| v = qmp_input_get_visitor(qiv);
|+ visit_start_struct(v, NULL, NULL, 0, &err);
|+ if (err) {
|+ goto out;
|+ }
| visit_type_BlockdevBackup_members(v, &arg, &err);
|+ visit_end_struct(v, err ? NULL : &err);
| if (err) {
| goto out;
| }
|@@ -527,7 +715,9 @@ out:
| qmp_input_visitor_cleanup(qiv);
| qdv = qapi_dealloc_visitor_new();
| v = qapi_dealloc_get_visitor(qdv);
|+ visit_start_struct(v, NULL, NULL, 0, NULL);
| visit_type_BlockdevBackup_members(v, &arg, NULL);
|+ visit_end_struct(v, NULL);
| qapi_dealloc_visitor_cleanup(qdv);
| }
The use of 'err ? NULL : &err' is temporary; a later patch will
clean that up when it splits visit_end_struct().
Prior to this patch, the fact that there was no final
visit_end_struct() meant that even though we are using a strict
input visit, the marshalling code was not detecting excess input
at the top level (only in nested levels). Fortunately, we have
code in monitor.c:qmp_check_client_args() that also checks for
no excess arguments at the top level. But as the generated code
is more compact than the manual check, a later patch will clean
up monitor.c to drop the redundancy added here.
Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1461879932-9020-9-git-send-email-eblake@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
2016-04-28 23:45:16 +02:00
|
|
|
visit_start_struct(v, NULL, NULL, 0, NULL);
|
2016-03-03 17:16:46 +01:00
|
|
|
visit_type_UserDefOneList(v, "arg1", &arg1, NULL);
|
qapi: Split visit_end_struct() into pieces
As mentioned in previous patches, we want to call visit_end_struct()
functions unconditionally, so that visitors can release resources
tied up since the matching visit_start_struct() without also having
to worry about error priority if more than one error occurs.
Even though error_propagate() can be safely used to ignore a second
error during cleanup caused by a first error, it is simpler if the
cleanup cannot set an error. So, split out the error checking
portion (basically, input visitors checking for unvisited keys) into
a new function visit_check_struct(), which can be safely skipped if
any earlier errors are encountered, and leave the cleanup portion
(which never fails, but must be called unconditionally if
visit_start_struct() succeeded) in visit_end_struct().
Generated code in qapi-visit.c has diffs resembling:
|@@ -59,10 +59,12 @@ void visit_type_ACPIOSTInfo(Visitor *v,
| goto out_obj;
| }
| visit_type_ACPIOSTInfo_members(v, obj, &err);
|- error_propagate(errp, err);
|- err = NULL;
|+ if (err) {
|+ goto out_obj;
|+ }
|+ visit_check_struct(v, &err);
| out_obj:
|- visit_end_struct(v, &err);
|+ visit_end_struct(v);
| out:
and in qapi-event.c:
@@ -47,7 +47,10 @@ void qapi_event_send_acpi_device_ost(ACP
| goto out;
| }
| visit_type_q_obj_ACPI_DEVICE_OST_arg_members(v, ¶m, &err);
|- visit_end_struct(v, err ? NULL : &err);
|+ if (!err) {
|+ visit_check_struct(v, &err);
|+ }
|+ visit_end_struct(v);
| if (err) {
| goto out;
Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1461879932-9020-20-git-send-email-eblake@redhat.com>
[Conflict with a doc fixup resolved]
Signed-off-by: Markus Armbruster <armbru@redhat.com>
2016-04-28 23:45:27 +02:00
|
|
|
visit_end_struct(v);
|
2015-09-30 00:21:09 +02:00
|
|
|
qapi_dealloc_visitor_cleanup(qdv);
|
2011-07-19 21:50:46 +02:00
|
|
|
}
|
|
|
|
|
|
|
|
static void qmp_init_marshal(void)
|
|
|
|
{
|
2015-09-16 13:06:19 +02:00
|
|
|
qmp_register_command("my-command", qmp_marshal_my_command, QCO_NO_OPTIONS);
|
2011-07-19 21:50:46 +02:00
|
|
|
}
|
|
|
|
|
|
|
|
qapi_init(qmp_init_marshal);
|
2014-09-26 17:20:33 +02:00
|
|
|
|
|
|
|
=== scripts/qapi-event.py ===
|
|
|
|
|
2016-03-03 17:16:46 +01:00
|
|
|
Used to generate the event-related C code defined by a schema, with
|
|
|
|
implementations for qapi_event_send_FOO(). The following files are
|
|
|
|
created:
|
2014-09-26 17:20:33 +02:00
|
|
|
|
|
|
|
$(prefix)qapi-event.h - Function prototypes for each event type, plus an
|
|
|
|
enumeration of all event names
|
|
|
|
$(prefix)qapi-event.c - Implementation of functions to send an event
|
|
|
|
|
|
|
|
Example:
|
|
|
|
|
|
|
|
$ python scripts/qapi-event.py --output-dir="qapi-generated"
|
2015-04-02 13:32:16 +02:00
|
|
|
--prefix="example-" example-schema.json
|
2016-03-03 17:16:46 +01:00
|
|
|
$ cat qapi-generated/example-qapi-event.h
|
|
|
|
[Uninteresting stuff omitted...]
|
|
|
|
|
|
|
|
#ifndef EXAMPLE_QAPI_EVENT_H
|
|
|
|
#define EXAMPLE_QAPI_EVENT_H
|
|
|
|
|
|
|
|
#include "qapi/error.h"
|
|
|
|
#include "qapi/qmp/qdict.h"
|
|
|
|
#include "example-qapi-types.h"
|
|
|
|
|
|
|
|
|
|
|
|
void qapi_event_send_my_event(Error **errp);
|
|
|
|
|
|
|
|
typedef enum example_QAPIEvent {
|
|
|
|
EXAMPLE_QAPI_EVENT_MY_EVENT = 0,
|
|
|
|
EXAMPLE_QAPI_EVENT__MAX = 1,
|
|
|
|
} example_QAPIEvent;
|
|
|
|
|
|
|
|
extern const char *const example_QAPIEvent_lookup[];
|
|
|
|
|
|
|
|
#endif
|
2014-09-26 17:20:33 +02:00
|
|
|
$ cat qapi-generated/example-qapi-event.c
|
|
|
|
[Uninteresting stuff omitted...]
|
|
|
|
|
|
|
|
void qapi_event_send_my_event(Error **errp)
|
|
|
|
{
|
|
|
|
QDict *qmp;
|
2015-09-30 00:21:08 +02:00
|
|
|
Error *err = NULL;
|
2014-09-26 17:20:33 +02:00
|
|
|
QMPEventFuncEmit emit;
|
|
|
|
emit = qmp_event_get_func_emit();
|
|
|
|
if (!emit) {
|
|
|
|
return;
|
|
|
|
}
|
|
|
|
|
|
|
|
qmp = qmp_event_build_dict("MY_EVENT");
|
|
|
|
|
2015-09-30 00:21:08 +02:00
|
|
|
emit(EXAMPLE_QAPI_EVENT_MY_EVENT, qmp, &err);
|
2014-09-26 17:20:33 +02:00
|
|
|
|
2015-09-30 00:21:08 +02:00
|
|
|
error_propagate(errp, err);
|
2014-09-26 17:20:33 +02:00
|
|
|
QDECREF(qmp);
|
|
|
|
}
|
|
|
|
|
2015-09-16 13:06:12 +02:00
|
|
|
const char *const example_QAPIEvent_lookup[] = {
|
|
|
|
[EXAMPLE_QAPI_EVENT_MY_EVENT] = "MY_EVENT",
|
qapi: Don't let implicit enum MAX member collide
Now that we guarantee the user doesn't have any enum values
beginning with a single underscore, we can use that for our
own purposes. Renaming ENUM_MAX to ENUM__MAX makes it obvious
that the sentinel is generated.
This patch was mostly generated by applying a temporary patch:
|diff --git a/scripts/qapi.py b/scripts/qapi.py
|index e6d014b..b862ec9 100644
|--- a/scripts/qapi.py
|+++ b/scripts/qapi.py
|@@ -1570,6 +1570,7 @@ const char *const %(c_name)s_lookup[] = {
| max_index = c_enum_const(name, 'MAX', prefix)
| ret += mcgen('''
| [%(max_index)s] = NULL,
|+// %(max_index)s
| };
| ''',
| max_index=max_index)
then running:
$ cat qapi-{types,event}.c tests/test-qapi-types.c |
sed -n 's,^// \(.*\)MAX,s|\1MAX|\1_MAX|g,p' > list
$ git grep -l _MAX | xargs sed -i -f list
The only things not generated are the changes in scripts/qapi.py.
Rejecting enum members named 'MAX' is now useless, and will be dropped
in the next patch.
Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1447836791-369-23-git-send-email-eblake@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
[Rebased to current master, commit message tweaked]
Signed-off-by: Markus Armbruster <armbru@redhat.com>
2015-11-18 09:52:57 +01:00
|
|
|
[EXAMPLE_QAPI_EVENT__MAX] = NULL,
|
2014-09-26 17:20:33 +02:00
|
|
|
};
|
qapi: New QMP command query-qmp-schema for QMP introspection
qapi/introspect.json defines the introspection schema. It's designed
for QMP introspection, but should do for similar uses, such as QGA.
The introspection schema does not reflect all the rules and
restrictions that apply to QAPI schemata. A valid QAPI schema has an
introspection value conforming to the introspection schema, but the
converse is not true.
Introspection lowers away a number of schema details, and makes
implicit things explicit:
* The built-in types are declared with their JSON type.
All integer types are mapped to 'int', because how many bits we use
internally is an implementation detail. It could be pressed into
external interface service as very approximate range information,
but that's a bad idea. If we need range information, we better do
it properly.
* Implicit type definitions are made explicit, and given
auto-generated names:
- Array types, named by appending "List" to the name of their
element type, like in generated C.
- The enumeration types implicitly defined by simple union types,
named by appending "Kind" to the name of their simple union type,
like in generated C.
- Types that don't occur in generated C. Their names start with ':'
so they don't clash with the user's names.
* All type references are by name.
* The struct and union types are generalized into an object type.
* Base types are flattened.
* Commands take a single argument and return a single result.
Dictionary argument or list result is an implicit type definition.
The empty object type is used when a command takes no arguments or
produces no results.
The argument is always of object type, but the introspection schema
doesn't reflect that.
The 'gen': false directive is omitted as implementation detail.
The 'success-response' directive is omitted as well for now, even
though it's not an implementation detail, because it's not used by
QMP.
* Events carry a single data value.
Implicit type definition and empty object type use, just like for
commands.
The value is of object type, but the introspection schema doesn't
reflect that.
* Types not used by commands or events are omitted.
Indirect use counts as use.
* Optional members have a default, which can only be null right now
Instead of a mandatory "optional" flag, we have an optional default.
No default means mandatory, default null means optional without
default value. Non-null is available for optional with default
(possible future extension).
* Clients should *not* look up types by name, because type names are
not ABI. Look up the command or event you're interested in, then
follow the references.
TODO Should we hide the type names to eliminate the temptation?
New generator scripts/qapi-introspect.py computes an introspection
value for its input, and generates a C variable holding it.
It can generate awfully long lines. Marked TODO.
A new test-qmp-input-visitor test case feeds its result for both
tests/qapi-schema/qapi-schema-test.json and qapi-schema.json to a
QmpInputVisitor to verify it actually conforms to the schema.
New QMP command query-qmp-schema takes its return value from that
variable. Its reply is some 85KiBytes for me right now.
If this turns out to be too much, we have a couple of options:
* We can use shorter names in the JSON. Not the QMP style.
* Optionally return the sub-schema for commands and events given as
arguments.
Right now qmp_query_schema() sends the string literal computed by
qmp-introspect.py. To compute sub-schema at run time, we'd have to
duplicate parts of qapi-introspect.py in C. Unattractive.
* Let clients cache the output of query-qmp-schema.
It changes only on QEMU upgrades, i.e. rarely. Provide a command
query-qmp-schema-hash. Clients can have a cache indexed by hash,
and re-query the schema only when they don't have it cached. Even
simpler: put the hash in the QMP greeting.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
2015-09-16 13:06:28 +02:00
|
|
|
|
|
|
|
=== scripts/qapi-introspect.py ===
|
|
|
|
|
|
|
|
Used to generate the introspection C code for a schema. The following
|
|
|
|
files are created:
|
|
|
|
|
|
|
|
$(prefix)qmp-introspect.c - Defines a string holding a JSON
|
|
|
|
description of the schema.
|
|
|
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$(prefix)qmp-introspect.h - Declares the above string.
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Example:
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$ python scripts/qapi-introspect.py --output-dir="qapi-generated"
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--prefix="example-" example-schema.json
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$ cat qapi-generated/example-qmp-introspect.h
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[Uninteresting stuff omitted...]
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#ifndef EXAMPLE_QMP_INTROSPECT_H
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#define EXAMPLE_QMP_INTROSPECT_H
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extern const char example_qmp_schema_json[];
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#endif
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2016-03-03 17:16:46 +01:00
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$ cat qapi-generated/example-qmp-introspect.c
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[Uninteresting stuff omitted...]
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const char example_qmp_schema_json[] = "["
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"{\"arg-type\": \"0\", \"meta-type\": \"event\", \"name\": \"MY_EVENT\"}, "
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"{\"arg-type\": \"1\", \"meta-type\": \"command\", \"name\": \"my-command\", \"ret-type\": \"2\"}, "
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"{\"members\": [], \"meta-type\": \"object\", \"name\": \"0\"}, "
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"{\"members\": [{\"name\": \"arg1\", \"type\": \"[2]\"}], \"meta-type\": \"object\", \"name\": \"1\"}, "
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"{\"members\": [{\"name\": \"integer\", \"type\": \"int\"}, {\"default\": null, \"name\": \"string\", \"type\": \"str\"}], \"meta-type\": \"object\", \"name\": \"2\"}, "
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"{\"element-type\": \"2\", \"meta-type\": \"array\", \"name\": \"[2]\"}, "
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"{\"json-type\": \"int\", \"meta-type\": \"builtin\", \"name\": \"int\"}, "
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"{\"json-type\": \"string\", \"meta-type\": \"builtin\", \"name\": \"str\"}]";
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