block/nbd: extract the common cleanup code

The BDRVNBDState cleanup code is common in two places, add
nbd_clear_bdrvstate() function to do these cleanups.

Suggested-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Pan Nengyuan <pannengyuan@huawei.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <1575517528-44312-2-git-send-email-pannengyuan@huawei.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
[eblake: fix compilation error and commit message]
Signed-off-by: Eric Blake <eblake@redhat.com>
(cherry picked from commit 7f49366)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>

block/nbd.c

@@ -94,6 +94,19 @@ typedef struct BDRVNBDState {
 
 static int nbd_client_connect(BlockDriverState *bs, Error **errp);
 
+static void nbd_clear_bdrvstate(BDRVNBDState *s)
+{
+    object_unref(OBJECT(s->tlscreds));
+    qapi_free_SocketAddress(s->saddr);
+    s->saddr = NULL;
+    g_free(s->export);
+    s->export = NULL;
+    g_free(s->tlscredsid);
+    s->tlscredsid = NULL;
+    g_free(s->x_dirty_bitmap);
+    s->x_dirty_bitmap = NULL;
+}
+
 static void nbd_channel_error(BDRVNBDState *s, int ret)
 {
     if (ret == -EIO) {
@@ -1864,11 +1877,7 @@ static int nbd_process_options(BlockDriverState *bs, QDict *options,
 
  error:
     if (ret < 0) {
-        object_unref(OBJECT(s->tlscreds));
-        qapi_free_SocketAddress(s->saddr);
-        g_free(s->export);
-        g_free(s->tlscredsid);
-        g_free(s->x_dirty_bitmap);
+        nbd_clear_bdrvstate(s);
     }
     qemu_opts_del(opts);
     return ret;
@@ -1947,12 +1956,7 @@ static void nbd_close(BlockDriverState *bs)
     BDRVNBDState *s = bs->opaque;
 
     nbd_client_close(bs);
-
-    object_unref(OBJECT(s->tlscreds));
-    qapi_free_SocketAddress(s->saddr);
-    g_free(s->export);
-    g_free(s->tlscredsid);
-    g_free(s->x_dirty_bitmap);
+    nbd_clear_bdrvstate(s);
 }
 
 static int64_t nbd_getlength(BlockDriverState *bs)