block/backup: support bitmap sync modes for non-bitmap backups

Accept bitmaps and sync policies for the other backup modes.
This allows us to do things like create a bitmap synced to a full backup
without a transaction, or start a resumable backup process.

Some combinations don't make sense, though:

- NEVER policy combined with any non-BITMAP mode doesn't do anything,
  because the bitmap isn't used for input or output.
  It's harmless, but is almost certainly never what the user wanted.

- sync=NONE is more questionable. It can't use on-success because this
  job never completes with success anyway, and the resulting artifact
  of 'always' is suspect: because we start with a full bitmap and only
  copy out segments that get written to, the final output bitmap will
  always be ... a fully set bitmap.

  Maybe there's contexts in which bitmaps make sense for sync=none,
  but not without more severe changes to the current job, and omitting
  it here doesn't prevent us from adding it later.

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Message-id: 20190716000117.25219-11-jsnow@redhat.com
Signed-off-by: John Snow <jsnow@redhat.com>

1 files changed, 1 insertions, 7 deletions

diff --git a/block/backup.c b/block/backup.c
index 9e1382ec5c..a9be07258c 100644
--- a/block/backup.c
+++ b/block/backup.c
@@ -697,7 +697,7 @@ BlockJob *backup_job_create(const char *job_id, BlockDriverState *bs,
         return NULL;
     }
 
-    if (sync_mode == MIRROR_SYNC_MODE_BITMAP) {
+    if (sync_bitmap) {
         /* If we need to write to this bitmap, check that we can: */
         if (bitmap_mode != BITMAP_SYNC_MODE_NEVER &&
             bdrv_dirty_bitmap_check(sync_bitmap, BDRV_BITMAP_DEFAULT, errp)) {
@@ -708,12 +708,6 @@ BlockJob *backup_job_create(const char *job_id, BlockDriverState *bs,
         if (bdrv_dirty_bitmap_create_successor(bs, sync_bitmap, errp) < 0) {
             return NULL;
         }
-    } else if (sync_bitmap) {
-        error_setg(errp,
-                   "a bitmap was given to backup_job_create, "
-                   "but it received an incompatible sync_mode (%s)",
-                   MirrorSyncMode_str(sync_mode));
-        return NULL;
     }
 
     len = bdrv_getlength(bs);