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/transaction.json b/qapi/transaction.json
index d175b5f..381a2df 100644
--- a/qapi/transaction.json
+++ b/qapi/transaction.json
@@ -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:
