Catch transient errors, wait and retry

I see occasionally an interrupted system call exception from async_inotify:

https://github.com/janestreet/async_inotify/blob/aaeedfaa4751d18b741ba2f82ef03a88e749e5f0/src/async_inotify.ml#L97

If this happens, I'll log the backtrace, wait 5 seconds and try again.

Signed-off-by: David Scott <dave@recoil.org>

Author: djs55

main.ml

@@ -765,8 +765,7 @@ let rec diff a b = match a with
   | a :: aa ->
     if List.mem b a then diff aa b else a :: (diff aa b)
 
-let watch_volume_plugins ~root_dir ~switch_path =
-  let root_dir = Filename.concat root_dir "volume" in
+let watch_volume_plugins ~root_dir ~switch_path ~pipe =
   let create switch_path root_dir name =
     if Hashtbl.mem servers name
       then return ()
@@ -794,11 +793,8 @@ let watch_volume_plugins ~root_dir ~switch_path =
     Deferred.all_ignore (List.map ~f:(create switch_path root_dir) (diff needed got_already))
     >>= fun () ->
     Deferred.all_ignore (List.map ~f:(destroy switch_path) (diff got_already needed)) in
-  Async_inotify.create ~recursive:false ~watch_new_dirs:false root_dir
-  >>= fun (watch, _) ->
   sync ~root_dir ~switch_path
   >>= fun () ->
-  let pipe = Async_inotify.pipe watch in
   let open Async_inotify.Event in
   let rec loop () =
     ( Pipe.read pipe >>= function
@@ -823,8 +819,7 @@ let watch_volume_plugins ~root_dir ~switch_path =
     loop () in
   loop ()
 
-let watch_datapath_plugins ~root_dir =
-  let root_dir = Filename.concat root_dir "datapath" in
+let watch_datapath_plugins ~root_dir ~pipe =
   let sync ~root_dir =
     Sys.readdir root_dir
     >>= fun names ->
@@ -833,11 +828,8 @@ let watch_datapath_plugins ~root_dir =
     Deferred.all_ignore (List.map ~f:(Datapath_plugins.register root_dir) (diff needed got_already))
     >>= fun () ->
     Deferred.all_ignore (List.map ~f:(Datapath_plugins.unregister root_dir) (diff got_already needed)) in
-  Async_inotify.create ~recursive:false ~watch_new_dirs:false root_dir
-  >>= fun (watch, _) ->
   sync ~root_dir
   >>= fun () ->
-  let pipe = Async_inotify.pipe watch in
   let open Async_inotify.Event in
   let rec loop () =
     ( Pipe.read pipe >>= function
@@ -865,14 +857,32 @@ let watch_datapath_plugins ~root_dir =
 let main ~root_dir ~state_path ~switch_path =
   Attached_SRs.reload state_path
   >>= fun () ->
-  Deferred.all_unit [
-    watch_volume_plugins ~root_dir ~switch_path;
-    watch_datapath_plugins ~root_dir
-  ]
+  let datapath_root = Filename.concat root_dir "datapath" in
+  Async_inotify.create ~recursive:false ~watch_new_dirs:false datapath_root
+  >>= fun (watch, _) ->
+  let datapath = Async_inotify.pipe watch in
+  let volume_root = Filename.concat root_dir "volume" in
+  Async_inotify.create ~recursive:false ~watch_new_dirs:false volume_root
+  >>= fun (watch, _) ->
+  let volume = Async_inotify.pipe watch in
 
-let main ~root_dir ~state_path ~switch_path =
-  let (_: unit Deferred.t) = main ~root_dir ~state_path ~switch_path in
-  never_returns (Scheduler.go ())
+  let rec loop () =
+    Monitor.try_with
+      (fun () ->
+        Deferred.all_unit [
+          watch_volume_plugins ~root_dir:volume_root ~switch_path ~pipe:volume;
+          watch_datapath_plugins ~root_dir:datapath_root ~pipe:datapath
+        ]
+      )
+    >>= function
+    | Ok () ->
+      info "main thread shutdown cleanly";
+      return ()
+    | Error x ->
+      error "main thread failed with %s" (Exn.to_string x);
+      Clock.after (Time.Span.of_sec 5.) >>= fun () -> 
+      loop () in
+  loop ()
 
 open Xcp_service
 
@@ -917,5 +927,20 @@ let _ =
     use_syslog := true;
     info "Daemonisation successful.";
   end;
-  main ~root_dir:!root_dir ~state_path:!state_path ~switch_path:!Xcp_client.switch_path
+  let (_: unit Deferred.t) =
+    let rec loop () =
+      Monitor.try_with
+        (fun () ->
+          main ~root_dir:!root_dir ~state_path:!state_path ~switch_path:!Xcp_client.switch_path
+        )
+      >>= function
+      | Ok () ->
+        info "main thread shutdown cleanly";
+        return ()
+      | Error x ->
+        error "main thread failed with %s" (Exn.to_string x);
+        Clock.after (Time.Span.of_sec 5.) >>= fun () -> 
+        loop () in
+    loop () in
+  never_returns (Scheduler.go ())