block/backup: add 'never' policy to bitmap sync mode

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 <jsnow@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Message-id: 20190709232550.10724-7-jsnow@redhat.com
Signed-off-by: John Snow <jsnow@redhat.com>

diff --git a/block/backup.c b/block/backup.c
index 2b4c5c23e4e5eaa3baab945128c052f1cf40720f..d07b838930fc5c043bdae2105eb92ebc160fe5cd 100644 (file)
--- a/block/backup.c
+++ b/block/backup.c
@@ -274,8 +274,11 @@ 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 {

diff --git a/qapi/block-core.json b/qapi/block-core.json
index dd926f782855367509152a091811ada92187402e..06e34488a30cfca70ac85ee4977ed39bebfe1b46 100644 (file)
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -1146,10 +1146,13 @@
 # @on-success: The bitmap is only synced when the operation is successful.
 #              This is the behavior always used for 'INCREMENTAL' backups.
 #
+# @never: The bitmap is never synchronized with the operation, and is
+#         treated solely as a read-only manifest of blocks to copy.
+#
 # Since: 4.2
 ##
 { 'enum': 'BitmapSyncMode',
-  'data': ['on-success'] }
+  'data': ['on-success', 'never'] }
 
 ##
 # @MirrorCopyMode: