blockdev: loosen restrictions on drive-backup source node

We mandate that the source node must be a root node; but there's no reason
I am aware of that it needs to be restricted to such. In some cases, we need
to make sure that there's a medium present, but in the general case we can
allow the backup job itself to do the graph checking.

This patch helps improve the error message when you try to backup from
the same node more than once, which is reflected in the change to test
056.

For backups with bitmaps, it will also show a better error message that
the bitmap is in use instead of giving you something cryptic like "need
a root node."

Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1707303
Signed-off-by: John Snow <jsnow@redhat.com>
Message-id: 20190521210053.8864-1-jsnow@redhat.com
Signed-off-by: Max Reitz <mreitz@redhat.com>

diff --git a/blockdev.c b/blockdev.c
index 79fbac8450816b58091d38d53f57c9a656740822..bc339d78184423171cc7ef0009632e954a3282d1 100644 (file)
--- a/blockdev.c
+++ b/blockdev.c
@@ -3450,11 +3450,16 @@ static BlockJob *do_drive_backup(DriveBackup *backup, JobTxn *txn,
         backup->compress = false;
     }
 
-    bs = qmp_get_root_bs(backup->device, errp);
+    bs = bdrv_lookup_bs(backup->device, backup->device, errp);
     if (!bs) {
         return NULL;
     }
 
+    if (!bs->drv) {
+        error_setg(errp, "Device has no medium");
+        return NULL;
+    }
+
     aio_context = bdrv_get_aio_context(bs);
     aio_context_acquire(aio_context);
 

diff --git a/tests/qemu-iotests/056 b/tests/qemu-iotests/056
index 3df323984d9c7300758e60f97247cada706b5fbf..f40fc11a09df8d39b576e3539a29c77e32f007bf 100755 (executable)
--- a/tests/qemu-iotests/056
+++ b/tests/qemu-iotests/056
@@ -214,7 +214,7 @@ class BackupTest(iotests.QMPTestCase):
         res = self.vm.qmp('query-block-jobs')
         self.assert_qmp(res, 'return[0]/status', 'concluded')
         # Leave zombie job un-dismissed, observe a failure:
-        res = self.qmp_backup_and_wait(serror='Need a root block node',
+        res = self.qmp_backup_and_wait(serror="Node 'drive0' is busy: block device is in use by block job: backup",
                                        device='drive0', format=iotests.imgfmt,
                                        sync='full', target=self.dest_img,
                                        auto_dismiss=False)