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>

4 files changed, 8 insertions, 2 deletions

diff --git a/block/backup.c b/block/backup.c
index 79652bf57b..0151e84395 100644
--- a/block/backup.c
+++ b/block/backup.c
@@ -361,6 +361,7 @@ 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)
@@ -458,7 +459,7 @@ BlockJob *backup_job_create(const char *job_id, BlockDriverState *bs,
     }
 
     cbw = bdrv_cbw_append(bs, target, filter_node_name, discard_source,
-                          perf->min_cluster_size, &bcs, errp);
+                          perf->min_cluster_size, &bcs, on_cbw_error, errp);
     if (!cbw) {
         goto error;
     }
diff --git a/block/copy-before-write.c b/block/copy-before-write.c
index fd470f5f92..00af0b18ac 100644
--- a/block/copy-before-write.c
+++ b/block/copy-before-write.c
@@ -551,6 +551,7 @@ BlockDriverState *bdrv_cbw_append(BlockDriverState *source,
                                   bool discard_source,
                                   uint64_t min_cluster_size,
                                   BlockCopyState **bcs,
+                                  OnCbwError on_cbw_error,
                                   Error **errp)
 {
     BDRVCopyBeforeWriteState *state;
@@ -568,6 +569,7 @@ BlockDriverState *bdrv_cbw_append(BlockDriverState *source,
     }
     qdict_put_str(opts, "file", bdrv_get_node_name(source));
     qdict_put_str(opts, "target", bdrv_get_node_name(target));
+    qdict_put_str(opts, "on-cbw-error", OnCbwError_str(on_cbw_error));
 
     if (min_cluster_size > INT64_MAX) {
         error_setg(errp, "min-cluster-size too large: %" PRIu64 " > %" PRIi64,
diff --git a/block/copy-before-write.h b/block/copy-before-write.h
index 2a5d4ba693..eb93364e85 100644
--- a/block/copy-before-write.h
+++ b/block/copy-before-write.h
@@ -42,6 +42,7 @@ BlockDriverState *bdrv_cbw_append(BlockDriverState *source,
                                   bool discard_source,
                                   uint64_t min_cluster_size,
                                   BlockCopyState **bcs,
+                                  OnCbwError on_cbw_error,
                                   Error **errp);
 void bdrv_cbw_drop(BlockDriverState *bs);
 
diff --git a/block/replication.c b/block/replication.c
index d6625c51fe..07f274de9e 100644
--- a/block/replication.c
+++ b/block/replication.c
@@ -583,7 +583,9 @@ static void replication_start(ReplicationState *rs, ReplicationMode mode,
                                 0, MIRROR_SYNC_MODE_NONE, NULL, 0, false, false,
                                 NULL, &perf,
                                 BLOCKDEV_ON_ERROR_REPORT,
-                                BLOCKDEV_ON_ERROR_REPORT, JOB_INTERNAL,
+                                BLOCKDEV_ON_ERROR_REPORT,
+                                ON_CBW_ERROR_BREAK_GUEST_WRITE,
+                                JOB_INTERNAL,
                                 backup_job_completed, bs, NULL, &local_err);
         if (local_err) {
             error_propagate(errp, local_err);