block/nbd: fix how state is cleared on nbd_open() failure paths

We have two "return error" paths in nbd_open() after
nbd_process_options(). Actually we should call nbd_clear_bdrvstate()
on these paths. Interesting that nbd_process_options() calls
nbd_clear_bdrvstate() by itself.

Let's fix leaks and refactor things to be more obvious:

- intialize yank at top of nbd_open()
- move yank cleanup to nbd_clear_bdrvstate()
- refactor nbd_open() so that all failure paths except for
  yank-register goes through nbd_clear_bdrvstate()

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Roman Kagan <rvkagan@yandex-team.ru>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20210610100802.5888-4-vsementsov@virtuozzo.com>
Signed-off-by: Eric Blake <eblake@redhat.com>

block/nbd.c

@@ -152,8 +152,12 @@ static void nbd_co_establish_connection_cancel(BlockDriverState *bs,
 static int nbd_client_handshake(BlockDriverState *bs, Error **errp);
 static void nbd_yank(void *opaque);
 
-static void nbd_clear_bdrvstate(BDRVNBDState *s)
+static void nbd_clear_bdrvstate(BlockDriverState *bs)
 {
+    BDRVNBDState *s = (BDRVNBDState *)bs->opaque;
+
+    yank_unregister_instance(BLOCKDEV_YANK_INSTANCE(bs->node_name));
+
     object_unref(OBJECT(s->tlscreds));
     qapi_free_SocketAddress(s->saddr);
     s->saddr = NULL;
@@ -2275,9 +2279,6 @@ static int nbd_process_options(BlockDriverState *bs, QDict *options,
     ret = 0;
 
  error:
-    if (ret < 0) {
-        nbd_clear_bdrvstate(s);
-    }
     qemu_opts_del(opts);
     return ret;
 }
@@ -2288,11 +2289,6 @@ static int nbd_open(BlockDriverState *bs, QDict *options, int flags,
     int ret;
     BDRVNBDState *s = (BDRVNBDState *)bs->opaque;
 
-    ret = nbd_process_options(bs, options, errp);
-    if (ret < 0) {
-        return ret;
-    }
-
     s->bs = bs;
     qemu_co_mutex_init(&s->send_mutex);
     qemu_co_queue_init(&s->free_sema);
@@ -2301,20 +2297,23 @@ static int nbd_open(BlockDriverState *bs, QDict *options, int flags,
         return -EEXIST;
     }
 
+    ret = nbd_process_options(bs, options, errp);
+    if (ret < 0) {
+        goto fail;
+    }
+
     /*
      * establish TCP connection, return error if it fails
      * TODO: Configurable retry-until-timeout behaviour.
      */
     if (nbd_establish_connection(bs, s->saddr, errp) < 0) {
-        yank_unregister_instance(BLOCKDEV_YANK_INSTANCE(bs->node_name));
-        return -ECONNREFUSED;
+        ret = -ECONNREFUSED;
+        goto fail;
     }
 
     ret = nbd_client_handshake(bs, errp);
     if (ret < 0) {
-        yank_unregister_instance(BLOCKDEV_YANK_INSTANCE(bs->node_name));
-        nbd_clear_bdrvstate(s);
-        return ret;
+        goto fail;
     }
     /* successfully connected */
     s->state = NBD_CLIENT_CONNECTED;
@@ -2326,6 +2325,10 @@ static int nbd_open(BlockDriverState *bs, QDict *options, int flags,
     aio_co_schedule(bdrv_get_aio_context(bs), s->connection_co);
 
     return 0;
+
+fail:
+    nbd_clear_bdrvstate(bs);
+    return ret;
 }
 
 static int nbd_co_flush(BlockDriverState *bs)
@@ -2369,11 +2372,8 @@ static void nbd_refresh_limits(BlockDriverState *bs, Error **errp)
 
 static void nbd_close(BlockDriverState *bs)
 {
-    BDRVNBDState *s = bs->opaque;
-
     nbd_client_close(bs);
-    yank_unregister_instance(BLOCKDEV_YANK_INSTANCE(bs->node_name));
-    nbd_clear_bdrvstate(s);
+    nbd_clear_bdrvstate(bs);
 }
 
 /*