block/backup: loosen restriction on readonly bitmaps

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>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Message-id: 20190709232550.10724-19-jsnow@redhat.com
Signed-off-by: John Snow <jsnow@redhat.com>

block-backup-loosen-restriction-on-readonly-bitmaps.patch

@@ -0,0 +1,51 @@
+From 801e9452bc80a38ee26fe12ba42356851acd6a9e Mon Sep 17 00:00:00 2001
+From: John Snow <jsnow@redhat.com>
+Date: Mon, 29 Jul 2019 16:35:54 -0400
+Subject: [PATCH] block/backup: loosen restriction on readonly bitmaps
+
+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>
+Reviewed-by: Max Reitz <mreitz@redhat.com>
+Message-id: 20190709232550.10724-19-jsnow@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 84a56337ac..59ac2c0396 100644
+--- a/block/backup.c
++++ b/block/backup.c
+@@ -606,6 +606,12 @@ 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 34c8b651e1..efb69d343a 100644
+--- a/blockdev.c
++++ b/blockdev.c
+@@ -3533,7 +3533,7 @@ 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;
+         }
+     }
+-- 
+2.27.0
+