block: use bdrv_get_device_or_node_name() in error messages

There are several error messages that identify a BlockDriverState by
its device name. However those errors can be produced in nodes that
don't have a device name associated.

In those cases we should use bdrv_get_device_or_node_name() to fall
back to the node name and produce a more meaningful message. The
messages are also updated to use the more generic term 'node' instead
of 'device'.

Signed-off-by: Alberto Garcia <berto@igalia.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-id: 9823a1f0514fdb0692e92868661c38a9e00a12d6.1428485266.git.berto@igalia.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
diff --git a/block/qcow.c b/block/qcow.c
index 0558969..ab89328 100644
--- a/block/qcow.c
+++ b/block/qcow.c
@@ -124,7 +124,7 @@
         snprintf(version, sizeof(version), "QCOW version %" PRIu32,
                  header.version);
         error_set(errp, QERR_UNKNOWN_BLOCK_FORMAT_FEATURE,
-                  bdrv_get_device_name(bs), "qcow", version);
+                  bdrv_get_device_or_node_name(bs), "qcow", version);
         ret = -ENOTSUP;
         goto fail;
     }
@@ -229,9 +229,9 @@
     }
 
     /* Disable migration when qcow images are used */
-    error_set(&s->migration_blocker,
-              QERR_BLOCK_FORMAT_FEATURE_NOT_SUPPORTED,
-              "qcow", bdrv_get_device_name(bs), "live migration");
+    error_setg(&s->migration_blocker, "The qcow format used by node '%s' "
+               "does not support live migration",
+               bdrv_get_device_or_node_name(bs));
     migrate_add_blocker(s->migration_blocker);
 
     qemu_co_mutex_init(&s->lock);