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block/copy-before-write: add on-cbw-error open parameter

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Currently, behavior on copy-before-write operation failure is simple:
report error to the guest.

Let's implement alternative behavior: break the whole copy-before-write
process (and corresponding backup job or NBD client) but keep guest
working. It's needed if we consider guest stability as more important.

The realisation is simple: on copy-before-write failure we set
s->snapshot_ret and continue guest operations. s->snapshot_ret being
set will lead to all further snapshot API requests. Note that all
in-flight snapshot-API requests may still success: we do wait for them
on BREAK_SNAPSHOT-failure path in cbw_do_copy_before_write().

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@openvz.org>
Reviewed-by: Hanna Reitz <hreitz@redhat.com>
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
This commit is contained in:
Vladimir Sementsov-Ogievskiy 2022-04-07 16:27:21 +03:00 • committed by Vladimir Sementsov-Ogievskiy
parent 79ef0cebb5
commit f1bb39a8a5
2 changed files with 54 additions and 3 deletions
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25
qapi/block-core.json
View file

@ -4184,6 +4184,25 @@
'base': 'BlockdevOptionsGenericFormat',
'data': { '*bottom': 'str' } }
##
# @OnCbwError:
#
# An enumeration of possible behaviors for copy-before-write operation
# failures.
#
# @break-guest-write: report the error to the guest. This way, the guest
# will not be able to overwrite areas that cannot be
# backed up, so the backup process remains valid.
#
# @break-snapshot: continue guest write. Doing so will make the provided
# snapshot state invalid and any backup or export
# process based on it will finally fail.
#
# Since: 7.1
##
{ 'enum': 'OnCbwError',
'data': [ 'break-guest-write', 'break-snapshot' ] }
##
# @BlockdevOptionsCbw:
#
@ -4205,11 +4224,15 @@
# modifications (or removing) of specified bitmap doesn't
# influence the filter. (Since 7.0)
#
# @on-cbw-error: Behavior on failure of copy-before-write operation.
# Default is @break-guest-write. (Since 7.1)
#
# Since: 6.2
##
{ 'struct': 'BlockdevOptionsCbw',
'base': 'BlockdevOptionsGenericFormat',
'data': { 'target': 'BlockdevRef', '*bitmap': 'BlockDirtyBitmap' } }
'data': { 'target': 'BlockdevRef', '*bitmap': 'BlockDirtyBitmap',
'*on-cbw-error': 'OnCbwError' } }
##
# @BlockdevOptions: