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.

Reviewed-by: Max Reitz <mreitz@redhat.com>
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 b25e6179cf..a59962cea8 100644
--- a/block/backup.c
+++ b/block/backup.c
@@ -607,6 +607,12 @@ 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 5dfaa976c9..3e30bc2ca7 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -3489,7 +3489,7 @@ static BlockJob *do_backup_common(BackupCommon *backup,
                        "when providing a bitmap");
             return NULL;
         }
-        if (bdrv_dirty_bitmap_check(bmap, BDRV_BITMAP_DEFAULT, errp)) {
+        if (bdrv_dirty_bitmap_check(bmap, BDRV_BITMAP_ALLOW_RO, errp)) {
             return NULL;
         }
     }
-- 
2.21.0