blockdev-backup: Add error handling option for copy-before-write jobs

This patch extends the blockdev-backup QMP command to allow users to specify
how to behave when IO errors occur during copy-before-write operations.
Previously, the behavior was fixed and could not be controlled by the user.

The new 'on-cbw-error' option can be set to one of two values:
- 'break-guest-write': Forwards the IO error to the guest and triggers
  the on-source-error policy. This preserves snapshot integrity at the
  expense of guest IO operations.
- 'break-snapshot': Allows the guest OS to continue running normally,
  but invalidates the snapshot and aborts related jobs. This prioritizes
  guest operation over backup consistency.

This enhancement provides more flexibility for backup operations in different
environments where requirements for guest availability versus backup
consistency may vary.

The default behavior remains unchanged to maintain backward compatibility.

Signed-off-by: Raman Dzehtsiar <Raman.Dzehtsiar@gmail.com>
Message-ID: <20250414090025.828660-1-Raman.Dzehtsiar@gmail.com>
Acked-by: Markus Armbruster <armbru@redhat.com>
[vsementsov: fix long lines]
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Tested-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>

1 files changed, 2 insertions, 0 deletions

diff --git a/include/block/block_int-global-state.h b/include/block/block_int-global-state.h
index eb2d92a226..0d93783763 100644
--- a/include/block/block_int-global-state.h
+++ b/include/block/block_int-global-state.h
@@ -179,6 +179,7 @@ void mirror_start(const char *job_id, BlockDriverState *bs,
  *        all ".has_*" fields are ignored.
  * @on_source_error: The action to take upon error reading from the source.
  * @on_target_error: The action to take upon error writing to the target.
+ * @on_cbw_error: The action to take upon error in copy-before-write operations.
  * @creation_flags: Flags that control the behavior of the Job lifetime.
  *                  See @BlockJobCreateFlags
  * @cb: Completion function for the job.
@@ -198,6 +199,7 @@ BlockJob *backup_job_create(const char *job_id, BlockDriverState *bs,
                             BackupPerf *perf,
                             BlockdevOnError on_source_error,
                             BlockdevOnError on_target_error,
+                            OnCbwError on_cbw_error,
                             int creation_flags,
                             BlockCompletionFunc *cb, void *opaque,
                             JobTxn *txn, Error **errp);