fs-util: move fsync_directory_of_file() into generic code

This function used by the journal code is pretty useful generically,
let's move it to fs-util.c to make it useful for other code too.

src/basic/fs-util.c

@@ -967,3 +967,33 @@ int unlinkat_deallocate(int fd, const char *name, int flags) {
 
         return 0;
 }
+
+int fsync_directory_of_file(int fd) {
+        _cleanup_free_ char *path = NULL, *dn = NULL;
+        _cleanup_close_ int dfd = -1;
+        int r;
+
+        r = fd_verify_regular(fd);
+        if (r < 0)
+                return r;
+
+        r = fd_get_path(fd, &path);
+        if (r < 0)
+                return r;
+
+        if (!path_is_absolute(path))
+                return -EINVAL;
+
+        dn = dirname_malloc(path);
+        if (!dn)
+                return -ENOMEM;
+
+        dfd = open(dn, O_RDONLY|O_CLOEXEC|O_DIRECTORY);
+        if (dfd < 0)
+                return -errno;
+
+        if (fsync(dfd) < 0)
+                return -errno;
+
+        return 0;
+}

src/basic/fs-util.h

@@ -107,3 +107,5 @@ DEFINE_TRIVIAL_CLEANUP_FUNC(char*, unlink_and_free);
 int access_fd(int fd, int mode);
 
 int unlinkat_deallocate(int fd, const char *name, int flags);
+
+int fsync_directory_of_file(int fd);