qemu-iotests: qcow2.py
This adds a tool that is meant to inspect and edit qcow2 files in a low-level way, that wouldn't be possible with qemu-img/io, for example by adding yet unknown extensions or flags. This way we can test whether qemu deals properly with future backwards compatible extensions. For now, let's start with the image header and header extensions. Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Kevin Wolf
parent
eb09218077
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6e19b3c4e0
207
tests/qemu-iotests/qcow2.py
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207
tests/qemu-iotests/qcow2.py
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#!/usr/bin/env python
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import sys
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import struct
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import string
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class QcowHeaderExtension:
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def __init__(self, magic, length, data):
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self.magic = magic
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self.length = length
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self.data = data
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@classmethod
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def create(cls, magic, data):
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return QcowHeaderExtension(magic, len(data), data)
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class QcowHeader:
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uint32_t = 'I'
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uint64_t = 'Q'
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fields = [
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# Version 2 header fields
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[ uint32_t, '%#x', 'magic' ],
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[ uint32_t, '%d', 'version' ],
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[ uint64_t, '%#x', 'backing_file_offset' ],
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[ uint32_t, '%#x', 'backing_file_size' ],
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[ uint32_t, '%d', 'cluster_bits' ],
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[ uint64_t, '%d', 'size' ],
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[ uint32_t, '%d', 'crypt_method' ],
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[ uint32_t, '%d', 'l1_size' ],
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[ uint64_t, '%#x', 'l1_table_offset' ],
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[ uint64_t, '%#x', 'refcount_table_offset' ],
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[ uint32_t, '%d', 'refcount_table_clusters' ],
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[ uint32_t, '%d', 'nb_snapshots' ],
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[ uint64_t, '%#x', 'snapshot_offset' ],
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];
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fmt = '>' + ''.join(field[0] for field in fields)
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def __init__(self, fd):
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buf_size = struct.calcsize(QcowHeader.fmt)
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fd.seek(0)
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buf = fd.read(buf_size)
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header = struct.unpack(QcowHeader.fmt, buf)
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self.__dict__ = dict((field[2], header[i])
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for i, field in enumerate(QcowHeader.fields))
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self.cluster_size = 1 << self.cluster_bits
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fd.seek(self.get_header_length())
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self.load_extensions(fd)
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if self.backing_file_offset:
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fd.seek(self.backing_file_offset)
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self.backing_file = fd.read(self.backing_file_size)
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else:
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self.backing_file = None
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def get_header_length(self):
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if self.version == 2:
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return 72
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else:
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raise Exception("version != 2 not supported")
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def load_extensions(self, fd):
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self.extensions = []
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if self.backing_file_offset != 0:
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end = min(self.cluster_size, self.backing_file_offset)
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else:
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end = self.cluster_size
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while fd.tell() < end:
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(magic, length) = struct.unpack('>II', fd.read(8))
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if magic == 0:
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break
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else:
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padded = (length + 7) & ~7
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data = fd.read(padded)
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self.extensions.append(QcowHeaderExtension(magic, length, data))
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def update_extensions(self, fd):
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fd.seek(self.get_header_length())
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extensions = self.extensions
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extensions.append(QcowHeaderExtension(0, 0, ""))
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for ex in extensions:
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buf = struct.pack('>II', ex.magic, ex.length)
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fd.write(buf)
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fd.write(ex.data)
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if self.backing_file != None:
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self.backing_file_offset = fd.tell()
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fd.write(self.backing_file)
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if fd.tell() > self.cluster_size:
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raise Exception("I think I just broke the image...")
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def update(self, fd):
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header_bytes = self.get_header_length()
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self.update_extensions(fd)
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fd.seek(0)
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header = tuple(self.__dict__[f] for t, p, f in QcowHeader.fields)
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buf = struct.pack(QcowHeader.fmt, *header)
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buf = buf[0:header_bytes-1]
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fd.write(buf)
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def dump(self):
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for f in QcowHeader.fields:
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print "%-25s" % f[2], f[1] % self.__dict__[f[2]]
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print ""
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def dump_extensions(self):
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for ex in self.extensions:
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data = ex.data[:ex.length]
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if all(c in string.printable for c in data):
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data = "'%s'" % data
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else:
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data = "<binary>"
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print "Header extension:"
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print "%-25s %#x" % ("magic", ex.magic)
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print "%-25s %d" % ("length", ex.length)
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print "%-25s %s" % ("data", data)
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print ""
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def cmd_dump_header(fd):
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h = QcowHeader(fd)
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h.dump()
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h.dump_extensions()
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def cmd_add_header_ext(fd, magic, data):
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try:
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magic = int(magic, 0)
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except:
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print "'%s' is not a valid magic number" % magic
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sys.exit(1)
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h = QcowHeader(fd)
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h.extensions.append(QcowHeaderExtension.create(magic, data))
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h.update(fd)
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def cmd_del_header_ext(fd, magic):
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try:
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magic = int(magic, 0)
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except:
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print "'%s' is not a valid magic number" % magic
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sys.exit(1)
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h = QcowHeader(fd)
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found = False
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for ex in h.extensions:
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if ex.magic == magic:
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found = True
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h.extensions.remove(ex)
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if not found:
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print "No such header extension"
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return
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h.update(fd)
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cmds = [
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[ 'dump-header', cmd_dump_header, 0, 'Dump image header and header extensions' ],
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[ 'add-header-ext', cmd_add_header_ext, 2, 'Add a header extension' ],
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[ 'del-header-ext', cmd_del_header_ext, 1, 'Delete a header extension' ],
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]
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def main(filename, cmd, args):
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fd = open(filename, "r+b")
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try:
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for name, handler, num_args, desc in cmds:
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if name != cmd:
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continue
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elif len(args) != num_args:
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usage()
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return
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else:
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handler(fd, *args)
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return
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print "Unknown command '%s'" % cmd
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finally:
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fd.close()
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def usage():
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print "Usage: %s <file> <cmd> [<arg>, ...]" % sys.argv[0]
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print ""
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print "Supported commands:"
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for name, handler, num_args, desc in cmds:
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print " %-20s - %s" % (name, desc)
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if len(sys.argv) < 3:
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usage()
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sys.exit(1)
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main(sys.argv[1], sys.argv[2], sys.argv[3:])
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