[Qemu-devel] [PATCH 03/12] block/backup: add 'never' policy to bitmap sync mode

[John Snow]

This adds a "never" policy for bitmap synchronization. Regardless of if
the job succeeds or fails, we never update the bitmap. This can be used
to perform differential backups, or simply to avoid the job modifying a
bitmap.

Signed-off-by: John Snow <address@hidden>
---
 qapi/block-core.json | 6 +++++-
 block/backup.c       | 5 +++--
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/qapi/block-core.json b/qapi/block-core.json
index 6d05ad8f47..0332dcaabc 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -1146,10 +1146,14 @@
 # @conditional: The bitmap is only synchronized when the operation is 
successul.
 #               This is useful for Incremental semantics.
 #
+# @never: The bitmap is never synchronized with the operation, and is
+#         treated solely as a manifest of blocks to copy.
+#         This is useful for Differential semantics.
+#
 # Since: 4.1
 ##
 { 'enum': 'BitmapSyncMode',
-  'data': ['conditional'] }
+  'data': ['conditional', 'never'] }
 
 ##
 # @MirrorCopyMode:
diff --git a/block/backup.c b/block/backup.c
index c4f83d4ef7..627f724b68 100644
--- a/block/backup.c
+++ b/block/backup.c
@@ -265,8 +265,9 @@ static void backup_cleanup_sync_bitmap(BackupBlockJob *job, 
int ret)
     BdrvDirtyBitmap *bm;
     BlockDriverState *bs = blk_bs(job->common.blk);
 
-    if (ret < 0) {
-        /* Merge the successor back into the parent, delete nothing. */
+    if (ret < 0 || job->bitmap_mode == BITMAP_SYNC_MODE_NEVER) {
+        /* Failure, or we don't want to synchronize the bitmap.
+         * Merge the successor back into the parent, delete nothing. */
         bm = bdrv_reclaim_dirty_bitmap(bs, job->sync_bitmap, NULL);
         assert(bm);
     } else {
-- 
2.21.0