virtiofsd: Fix check of chown()'s return value

Otherwise you always get this warning when using --socket-group=users

 vhost socket failed to set group to users (100)

While here, print out the error if chown() fails.

Fixes: f6698f2b ("tools/virtiofsd: add support for --socket-group")
Signed-off-by: Greg Kurz <groug@kaod.org>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Message-Id: <162040394890.714971.15502455176528384778.stgit@bahia.lan>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>

tools/virtiofsd/fuse_virtio.c

@@ -1024,9 +1024,9 @@ static int fv_create_listen_socket(struct fuse_session *se)
     if (se->vu_socket_group) {
         struct group *g = getgrnam(se->vu_socket_group);
         if (g) {
-            if (!chown(se->vu_socket_path, -1, g->gr_gid)) {
+            if (chown(se->vu_socket_path, -1, g->gr_gid) == -1) {
                 fuse_log(FUSE_LOG_WARNING,
-                         "vhost socket failed to set group to %s (%d)\n",
+                         "vhost socket failed to set group to %s (%d): %m\n",
                          se->vu_socket_group, g->gr_gid);
             }
         }