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qapi: deprecate drive-backup

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Modern way is using blockdev-add + blockdev-backup, which provides a
lot more control on how target is opened.

As example of drive-backup problems consider the following:

User of drive-backup expects that target will be opened in the same
cache and aio mode as source. Corresponding logic is in
drive_backup_prepare(), where we take bs->open_flags of source.

It works rather bad if source was added by blockdev-add. Assume source
is qcow2 image. On blockdev-add we should specify aio and cache options
for file child of qcow2 node. What happens next:

drive_backup_prepare() looks at bs->open_flags of qcow2 source node.
But there no BDRV_O_NOCAHE neither BDRV_O_NATIVE_AIO: BDRV_O_NOCAHE is
places in bs->file->bs->open_flags, and BDRV_O_NATIVE_AIO is nowhere,
as file-posix parse options and simply set s->use_linux_aio.

The documentation is updated in a minimal way, so that drive-backup is
noted only as a deprecated command, and blockdev-backup used in most of
places.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
This commit is contained in:
Vladimir Sementsov-Ogievskiy 2021-11-04 09:58:11 +01:00
parent 24d6cc1fa1
commit 1084159b31
4 changed files with 51 additions and 18 deletions
Download patch file Download diff file Expand all files Collapse all files

5
qapi/block-core.json
View file

@ -1709,6 +1709,9 @@
# The operation can be stopped before it has completed using the
# block-job-cancel command.
#
# Features:
# @deprecated: This command is deprecated. Use @blockdev-backup instead.
#
# Returns: - nothing on success
# - If @device is not a valid block device, GenericError
#
@ -1724,7 +1727,7 @@
#
##
{ 'command': 'drive-backup', 'boxed': true,
'data': 'DriveBackup' }
'data': 'DriveBackup', 'features': ['deprecated'] }
##
# @blockdev-backup:

6
qapi/transaction.json
View file

@ -54,6 +54,10 @@
# @blockdev-snapshot-sync: since 1.1
# @drive-backup: Since 1.6
#
# Features:
# @deprecated: Member @drive-backup is deprecated. Use member
# @blockdev-backup instead.
#
# Since: 1.1
##
{ 'enum': 'TransactionActionKind',
@ -62,7 +66,7 @@
'block-dirty-bitmap-disable', 'block-dirty-bitmap-merge',
'blockdev-backup', 'blockdev-snapshot',
'blockdev-snapshot-internal-sync', 'blockdev-snapshot-sync',
'drive-backup' ] }
{ 'name': 'drive-backup', 'features': [ 'deprecated' ] } ] }
##
# @AbortWrapper: