With the "never" sync policy, we actually can utilize readonly bitmaps
now. Loosen the check at the QMP level, and tighten it based on
provided arguments down at the job creation level instead.

Signed-off-by: John Snow <jsnow@redhat.com>
---
 block/backup.c | 6 ++++++
 blockdev.c     | 2 +-
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/block/backup.c b/block/backup.c
index 495d8f71aa..4abe90d462 100644
--- a/block/backup.c
+++ b/block/backup.c
@@ -598,6 +598,12 @@ BlockJob *backup_job_create(const char *job_id, BlockDriverState *bs,
             return NULL;
         }
 
+        /* 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)) {
+            return NULL;
+        }
+
         /* Create a new bitmap, and freeze/disable this one. */
         if (bdrv_dirty_bitmap_create_successor(bs, sync_bitmap, errp) < 0) {
             return NULL;
diff --git a/blockdev.c b/blockdev.c
index d5b089a446..020ce7e960 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -3492,7 +3492,7 @@ static BlockJob *do_backup_common(BackupCommon *backup,
             error_setg(errp, "Bitmap '%s' could not be found", backup->bitmap);
             goto out;
         }
-        if (bdrv_dirty_bitmap_check(bmap, BDRV_BITMAP_DEFAULT, errp)) {
+        if (bdrv_dirty_bitmap_check(bmap, BDRV_BITMAP_ALLOW_RO, errp)) {
             goto out;
         }
     }
-- 
2.21.0

On 03.07.19 23:55, John Snow wrote:
> With the "never" sync policy, we actually can utilize readonly bitmaps
> now. Loosen the check at the QMP level, and tighten it based on
> provided arguments down at the job creation level instead.
> 
> Signed-off-by: John Snow <jsnow@redhat.com>
> ---
>  block/backup.c | 6 ++++++
>  blockdev.c     | 2 +-
>  2 files changed, 7 insertions(+), 1 deletion(-)

Reviewed-by: Max Reitz <mreitz@redhat.com>