From fae8bd3904642dd7ff582f4ad4e5e63b0cacbe6f Mon Sep 17 00:00:00 2001 From: Max Reitz Date: Wed, 13 May 2020 13:05:20 +0200 Subject: [PATCH] block: Add generic bdrv_inherited_options() After the series this patch belongs to, we want to have a common BdrvChildClass that encompasses all of child_file, child_format, and child_backing. Such a single class needs a single .inherit_options() implementation, and this patch introduces it. The next patch will show how the existing implementations can fall back to it just by passing appropriate BdrvChildRole and parent_is_format values. Signed-off-by: Max Reitz Message-Id: <20200513110544.176672-11-mreitz@redhat.com> Reviewed-by: Eric Blake Signed-off-by: Kevin Wolf --- block.c | 81 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 81 insertions(+) diff --git a/block.c b/block.c index a17c29f54b..9b0e13d537 100644 --- a/block.c +++ b/block.c @@ -1356,6 +1356,87 @@ const BdrvChildClass child_backing = { .set_aio_ctx = bdrv_child_cb_set_aio_ctx, }; +/* + * Returns the options and flags that a generic child of a BDS should + * get, based on the given options and flags for the parent BDS. + */ +static void __attribute__((unused)) + bdrv_inherited_options(BdrvChildRole role, bool parent_is_format, + int *child_flags, QDict *child_options, + int parent_flags, QDict *parent_options) +{ + int flags = parent_flags; + + /* + * First, decide whether to set, clear, or leave BDRV_O_PROTOCOL. + * Generally, the question to answer is: Should this child be + * format-probed by default? + */ + + /* + * Pure and non-filtered data children of non-format nodes should + * be probed by default (even when the node itself has BDRV_O_PROTOCOL + * set). This only affects a very limited set of drivers (namely + * quorum and blkverify when this comment was written). + * Force-clear BDRV_O_PROTOCOL then. + */ + if (!parent_is_format && + (role & BDRV_CHILD_DATA) && + !(role & (BDRV_CHILD_METADATA | BDRV_CHILD_FILTERED))) + { + flags &= ~BDRV_O_PROTOCOL; + } + + /* + * All children of format nodes (except for COW children) and all + * metadata children in general should never be format-probed. + * Force-set BDRV_O_PROTOCOL then. + */ + if ((parent_is_format && !(role & BDRV_CHILD_COW)) || + (role & BDRV_CHILD_METADATA)) + { + flags |= BDRV_O_PROTOCOL; + } + + /* + * If the cache mode isn't explicitly set, inherit direct and no-flush from + * the parent. + */ + qdict_copy_default(child_options, parent_options, BDRV_OPT_CACHE_DIRECT); + qdict_copy_default(child_options, parent_options, BDRV_OPT_CACHE_NO_FLUSH); + qdict_copy_default(child_options, parent_options, BDRV_OPT_FORCE_SHARE); + + if (role & BDRV_CHILD_COW) { + /* backing files are opened read-only by default */ + qdict_set_default_str(child_options, BDRV_OPT_READ_ONLY, "on"); + qdict_set_default_str(child_options, BDRV_OPT_AUTO_READ_ONLY, "off"); + } else { + /* Inherit the read-only option from the parent if it's not set */ + qdict_copy_default(child_options, parent_options, BDRV_OPT_READ_ONLY); + qdict_copy_default(child_options, parent_options, + BDRV_OPT_AUTO_READ_ONLY); + } + + /* + * bdrv_co_pdiscard() respects unmap policy for the parent, so we + * can default to enable it on lower layers regardless of the + * parent option. + */ + qdict_set_default_str(child_options, BDRV_OPT_DISCARD, "unmap"); + + /* Clear flags that only apply to the top layer */ + flags &= ~(BDRV_O_SNAPSHOT | BDRV_O_NO_BACKING | BDRV_O_COPY_ON_READ); + + if (role & BDRV_CHILD_METADATA) { + flags &= ~BDRV_O_NO_IO; + } + if (role & BDRV_CHILD_COW) { + flags &= ~BDRV_O_TEMPORARY; + } + + *child_flags = flags; +} + static int bdrv_open_flags(BlockDriverState *bs, int flags) { int open_flags = flags;