block: Avoid printing NULL string in error messages

Even for nodes that have a BlockBackend attached, bdrv_get_parent_name()
can return NULL if the BB is anonymous (e.g. it belongs to a block job
or a device that was created with a drive=<node-name> option).

Remove the information from the error message. The user probably knows
already why the node is still in use.
Signed-off-by: NKevin Wolf <kwolf@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>

blockdev.c

@@ -1803,8 +1803,7 @@ static void external_snapshot_prepare(BlkActionState *common,
     }
 
     if (bdrv_has_blk(state->new_bs)) {
-        error_setg(errp, "The snapshot is already in use by %s",
-                   bdrv_get_parent_name(state->new_bs));
+        error_setg(errp, "The snapshot is already in use");
         return;
     }
 
@@ -2532,8 +2531,7 @@ void qmp_x_blockdev_insert_medium(bool has_device, const char *device,
     }
 
     if (bdrv_has_blk(bs)) {
-        error_setg(errp, "Node '%s' is already in use by '%s'", node_name,
-                   bdrv_get_parent_name(bs));
+        error_setg(errp, "Node '%s' is already in use", node_name);
         return;
     }
 
@@ -3941,8 +3939,7 @@ void qmp_x_blockdev_del(bool has_id, const char *id,
             return;
         }
         if (bdrv_has_blk(bs)) {
-            error_setg(errp, "Node %s is in use by %s",
-                       node_name, bdrv_get_parent_name(bs));
+            error_setg(errp, "Node %s is in use", node_name);
             return;
         }
         aio_context = bdrv_get_aio_context(bs);

tests/qemu-iotests/085.out

@@ -68,9 +68,9 @@ Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/
 
 === Invalid command - snapshot node used as active layer ===
 
-{"error": {"class": "GenericError", "desc": "The snapshot is already in use by virtio0"}}
-{"error": {"class": "GenericError", "desc": "The snapshot is already in use by virtio0"}}
-{"error": {"class": "GenericError", "desc": "The snapshot is already in use by virtio1"}}
+{"error": {"class": "GenericError", "desc": "The snapshot is already in use"}}
+{"error": {"class": "GenericError", "desc": "The snapshot is already in use"}}
+{"error": {"class": "GenericError", "desc": "The snapshot is already in use"}}
 
 === Invalid command - snapshot node used as backing hd ===