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qapi: Introduce blockdev-group-snapshot-sync command

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This is a QAPI/QMP only command to take a snapshot of a group of
devices. This is similar to the blockdev-snapshot-sync command, except
blockdev-group-snapshot-sync accepts a list devices, filenames, and
formats.

It is attempted to keep the snapshot of the group atomic; if the
creation or open of any of the new snapshots fails, then all of
the new snapshots are abandoned, and the name of the snapshot image
that failed is returned.  The failure case should not interrupt
any operations.

Rather than use bdrv_close() along with a subsequent bdrv_open() to
perform the pivot, the original image is never closed and the new
image is placed 'in front' of the original image via manipulation
of the BlockDriverState fields.  Thus, once the new snapshot image
has been successfully created, there are no more failure points
before pivoting to the new snapshot.

This allows the group of disks to remain consistent with each other,
even across snapshot failures.

Signed-off-by: Jeff Cody <jcody@redhat.com>
Acked-by: Luiz Capitulino <lcapitulino@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Jeff Cody 2012-02-28 15:54:06 -05:00 • committed by Kevin Wolf
parent 64ca6aee4f
commit 8802d1fdd4
5 changed files with 257 additions and 0 deletions
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38
qapi-schema.json
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@ -1117,6 +1117,44 @@
##
{ 'command': 'block_resize', 'data': { 'device': 'str', 'size': 'int' }}
##
# @SnapshotDev
#
# @device: the name of the device to generate the snapshot from.
#
# @snapshot-file: the target of the new image. A new file will be created.
#
# @format: #optional the format of the snapshot image, default is 'qcow2'.
##
{ 'type': 'SnapshotDev',
'data': {'device': 'str', 'snapshot-file': 'str', '*format': 'str' } }
##
# @blockdev-group-snapshot-sync
#
# Generates a synchronous snapshot of a group of one or more block devices,
# as atomically as possible. If the snapshot of any device in the group
# fails, then the entire group snapshot will be abandoned and the
# appropriate error returned.
#
# List of:
# @SnapshotDev: information needed for the device snapshot
#
# Returns: nothing on success
# If @device is not a valid block device, DeviceNotFound
# If @device is busy, DeviceInUse will be returned
# If @snapshot-file can't be created, OpenFileFailed
# If @snapshot-file can't be opened, OpenFileFailed
# If @format is invalid, InvalidBlockFormat
#
# Note: The group snapshot attempt returns failure on the first snapshot
# device failure. Therefore, there will be only one device or snapshot file
# returned in an error condition, and subsequent devices will not have been
# attempted.
##
{ 'command': 'blockdev-group-snapshot-sync',
'data': { 'devlist': [ 'SnapshotDev' ] } }
##
# @blockdev-snapshot-sync
#