CP-13469: upgrade/downgrade: Use flock() instead of lockf()

Signed-off-by: Si Beaumont <[email protected]>

Author: simonjbeaumont

idl/flock.ml

@@ -0,0 +1,28 @@
+(*
+ * Copyright (C) 2015 Citrix Systems Inc.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published
+ * by the Free Software Foundation; version 2.1 only. with the special
+ * exception on linking described in file LICENSE.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Lesser General Public License for more details.
+ *)
+open Core.Std
+
+exception Could_not_obtain_lock of string
+
+let with_flock path f =
+  Unix.mkdir_p ~perm:0o700 (Filename.dirname path);
+  let fd = Unix.(openfile path ~mode:[O_WRONLY; O_CREAT] ~perm:0o644) in
+  let rec try_lock tries =
+    if tries > 0 then
+      if Unix.(flock fd Flock_command.lock_exclusive) then ()
+      else begin Unix.sleep 1; try_lock (tries - 1) end
+    else raise (Could_not_obtain_lock path)
+  in
+  try_lock 5;
+  protect ~f ~finally:(fun () -> Unix.(ignore (flock fd Flock_command.unlock)))

xenvm/xenvm.ml

@@ -82,15 +82,8 @@ let format config name filenames =
 (* LVM locking code can be seen here:
  * https://git.fedorahosted.org/cgit/lvm2.git/tree/lib/misc/lvm-flock.c#n141 *)
 let with_lvm_lock vg_name f =
-  let lock_dir = "/run/lock/lvm" in
-  let lock_path = Filename.concat lock_dir ("V_" ^ vg_name ^ ":aux") in
-  Lwt.catch (fun () ->
-    mkdir_rec lock_dir 0o0700;
-    Lwt_unix.(openfile lock_path [O_CREAT; O_TRUNC; O_RDWR] 0o644)
-    >>= fun fd ->
-    Lwt_unix.(lockf fd F_LOCK) 0;
-  ) (function _ -> fail (Failure "Could_not_obtain_lvm_lock")) >>= fun () ->
-  Lwt.finalize f (fun () -> Lwt_unix.unlink lock_path)
+  let lock_path = Filename.concat "/run/lock/lvm" ("V_" ^ vg_name ^ ":aux") in
+  Flock.with_flock lock_path f
 
 (* Change the label on the PV and revert it if the function [f] fails *)
 let with_label_change block magic f =