qapi: deprecate drive-backup
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>
diff --git a/qapi/block-core.json b/qapi/block-core.json
index 33e8507..1d3dd9c 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -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:
