fs-util: add API for fsync()ing parent dir of path

src/basic/fs-util.c

@@ -1484,6 +1484,30 @@ int fsync_path_at(int at_fd, const char *path) {
         return 0;
 }
 
+int fsync_parent_at(int at_fd, const char *path) {
+        _cleanup_close_ int opened_fd = -1;
+
+        if (isempty(path)) {
+                if (at_fd != AT_FDCWD)
+                        return fsync_directory_of_file(at_fd);
+
+                opened_fd = open("..", O_RDONLY|O_DIRECTORY|O_CLOEXEC);
+                if (opened_fd < 0)
+                        return -errno;
+
+                if (fsync(opened_fd) < 0)
+                        return -errno;
+
+                return 0;
+        }
+
+        opened_fd = openat(at_fd, path, O_PATH|O_CLOEXEC|O_NOFOLLOW);
+        if (opened_fd < 0)
+                return -errno;
+
+        return fsync_directory_of_file(opened_fd);
+}
+
 int syncfs_path(int atfd, const char *path) {
         _cleanup_close_ int fd = -1;