Add fsync for directory

src/irmin-pack/unix/gc_worker.ml

@@ -353,7 +353,8 @@ module Make (Args : Gc_args.S) = struct
     let out = Irmin.Type.to_json_string gc_output_t output in
     let* () = Io.write_string io ~off:Int63.zero out in
     let* () = Io.fsync io in
-    Io.close io
+    let* () = Io.close io in
+    Io.fsync_dir root
 
   (* No one catches errors when this function terminates. Write the result in a
      file and terminate. *)

src/irmin-pack/unix/io.ml

@@ -284,4 +284,17 @@ module Unix = struct
       Sys.remove path;
       Ok ()
     with Sys_error msg -> Error (`Sys_error msg)
+
+  let fsync_dir path =
+    try
+      let dirfd = Unix.openfile path Unix.[ O_RDONLY ] default_open_perm in
+      let fsync_result =
+        try
+          Unix.fsync dirfd;
+          Ok ()
+        with Unix.Unix_error (e, s1, s2) -> Error (`Io_misc (e, s1, s2))
+      in
+      Unix.close dirfd;
+      fsync_result
+    with Unix.Unix_error (e, s1, s2) -> Error (`Io_misc (e, s1, s2))
 end

src/irmin-pack/unix/io_intf.ml

@@ -140,6 +140,11 @@ module type S = sig
 
   val catch_misc_error :
     (unit -> 'a) -> ('a, [> `Io_misc of misc_error ]) result
+
+  val fsync_dir : string -> (unit, [> `Io_misc of misc_error ]) result
+  (** [fsync path] persists to the file system the directory in [path]. Note
+      that separate fsyncs are needed for persisting the files in the directory
+      [path]. *)
 end
 
 module type Sigs = sig