block/export: Don't ignore image activation error in blk_exp_add()

Currently, block exports can't handle inactive images correctly.
Incoming write requests would run into assertion failures. Make sure
that we return an error when creating an export can't activate the
image.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Acked-by: Fabiano Rosas <farosas@suse.de>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-ID: <20250204211407.381505-11-kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block/export/export.c

@@ -145,7 +145,11 @@ BlockExport *blk_exp_add(BlockExportOptions *export, Error **errp)
      * ctx was acquired in the caller.
      */
     bdrv_graph_rdlock_main_loop();
-    bdrv_activate(bs, NULL);
+    ret = bdrv_activate(bs, errp);
+    if (ret < 0) {
+        bdrv_graph_rdunlock_main_loop();
+        goto fail;
+    }
     bdrv_graph_rdunlock_main_loop();
 
     perm = BLK_PERM_CONSISTENT_READ;