ceph: name bdi ceph-%d instead of major:minor

The bdi_setup_and_register() helper doesn't help us since we bdi_init() in
create_client() and bdi_register() only when sget() succeeds.
Signed-off-by: Sage Weil <sage@newdream.net>

fs/ceph/super.c

@@ -910,6 +910,8 @@ static int ceph_compare_super(struct super_block *sb, void *data)
 /*
  * construct our own bdi so we can control readahead, etc.
  */
+static atomic_long_t bdi_seq = ATOMIC_INIT(0);
+
 static int ceph_register_bdi(struct super_block *sb, struct ceph_client *client)
 {
 	int err;
@@ -919,7 +921,8 @@ static int ceph_register_bdi(struct super_block *sb, struct ceph_client *client)
 		client->backing_dev_info.ra_pages =
 			(client->mount_args->rsize + PAGE_CACHE_SIZE - 1)
 			>> PAGE_SHIFT;
-	err = bdi_register_dev(&client->backing_dev_info, sb->s_dev);
+	err = bdi_register(&client->backing_dev_info, NULL, "ceph-%d",
+			   atomic_long_inc_return(&bdi_seq));
 	if (!err)
 		sb->s_bdi = &client->backing_dev_info;
 	return err;