qualify all return with Lwt, use Lwt.return_unit where possible

client_net.ml

@@ -23,7 +23,7 @@ let writev eth dst proto fillfn =
        (* Usually Netback_shutdown, because the client disconnected *)
        Log.err (fun f -> f "uncaught exception trying to send to client: @[%s@]"
                    (Printexc.to_string ex));
-       Lwt.return ()
+       Lwt.return_unit
     )
 
 class client_iface eth ~domid ~gateway_ip ~client_ip client_mac : client_link =
@@ -48,10 +48,10 @@ let input_arp ~fixed_arp ~iface request =
   match Arp_packet.decode request with
   | Error e ->
     Log.warn (fun f -> f "Ignored unknown ARP message: %a" Arp_packet.pp_error e);
-    Lwt.return ()
+    Lwt.return_unit
   | Ok arp ->
     match Client_eth.ARP.input fixed_arp arp with
-    | None -> return ()
+    | None -> Lwt.return_unit
     | Some response ->
       iface#writev `ARP (fun b -> Arp_packet.encode_into response b; Arp_packet.size)
 
@@ -60,8 +60,8 @@ let input_ipv4 get_ts cache ~iface ~router packet =
   match Nat_packet.of_ipv4_packet cache ~now:(get_ts ()) packet with
   | Error e ->
     Log.warn (fun f -> f "Ignored unknown IPv4 message: %a" Nat_packet.pp_error e);
-    Lwt.return ()
-  | Ok None -> Lwt.return ()
+    Lwt.return_unit
+  | Ok None -> Lwt.return_unit
   | Ok (Some packet) ->
     let `IPv4 (ip, _) = packet in
     let src = ip.Ipv4_packet.src in
@@ -69,7 +69,7 @@ let input_ipv4 get_ts cache ~iface ~router packet =
     else (
       Log.warn (fun f -> f "Incorrect source IP %a in IP packet from %a (dropping)"
                    Ipaddr.V4.pp src Ipaddr.V4.pp iface#other_ip);
-      return ()
+      Lwt.return_unit
     )
 
 (** Connect to a new client's interface and listen for incoming frames. *)
@@ -92,12 +92,12 @@ let add_vif get_ts { Dao.ClientVif.domid; device_id } ~client_ip ~router ~cleanu
                   Cstruct.hexdump_pp frame
               );
       Lwt.return_unit
-    | Error err -> Log.warn (fun f -> f "Invalid Ethernet frame: %s" err); return ()
+    | Error err -> Log.warn (fun f -> f "Invalid Ethernet frame: %s" err); Lwt.return_unit
     | Ok (eth, payload) ->
         match eth.Ethernet_packet.ethertype with
         | `ARP -> input_arp ~fixed_arp ~iface payload
         | `IPv4 -> input_ipv4 get_ts fragment_cache ~iface ~router payload
-        | `IPv6 -> return () (* TODO: oh no! *)
+        | `IPv6 -> Lwt.return_unit (* TODO: oh no! *)
   )
   >|= or_raise "Listen on client interface" Netback.pp_error
 
@@ -112,7 +112,7 @@ let add_client get_ts ~router vif client_ip =
         (fun ex ->
            Log.warn (fun f -> f "Error with client %a: %s"
                         Dao.ClientVif.pp vif (Printexc.to_string ex));
-           return ()
+           Lwt.return_unit
         )
     );
   cleanup_tasks

config.ml

@@ -30,8 +30,8 @@ let main =
       package "netchannel" ~min:"1.11.0";
       package "mirage-net-xen";
       package "ipaddr" ~min:"4.0.0";
-      package "mirage-qubes";
-      package "mirage-nat" ~min:"1.2.0";
+      package "mirage-qubes" ~min:"0.8.0";
+      package "mirage-nat" ~min:"2.0.0";
       package "mirage-logs";
       package "mirage-xen" ~min:"5.0.0";
     ]

dao.ml

@@ -3,7 +3,6 @@
 
 open Lwt.Infix
 open Qubes
-open Fw_utils
 open Astring
 
 let src = Logs.Src.create "dao" ~doc:"QubesDB data access"
@@ -68,13 +67,13 @@ let watch_clients fn =
     begin Lwt.catch
       (fun () -> directory ~handle backend_vifs)
       (function
-        | Xs_protocol.Enoent _ -> return []
-        | ex -> fail ex)
+        | Xs_protocol.Enoent _ -> Lwt.return []
+        | ex -> Lwt.fail ex)
     end >>= fun items ->
     Lwt_list.map_p (vifs ~handle) items >>= fun items ->
     fn (List.concat items |> VifMap.of_list);
     (* Wait for further updates *)
-    fail Xs_protocol.Eagain
+    Lwt.fail Xs_protocol.Eagain
   )
 
 type network_config = {

firewall.ml

@@ -1,7 +1,6 @@
 (* Copyright (C) 2015, Thomas Leonard <thomas.leonard@unikernel.com>
    See the README file for details. *)
 
-open Fw_utils
 open Packet
 open Lwt.Infix
 
@@ -32,7 +31,7 @@ let transmit_ipv4 packet iface =
             Log.warn (fun f -> f "Failed to write packet to %a: %s"
                          Ipaddr.V4.pp iface#other_ip
                          (Printexc.to_string ex));
-            Lwt.return ()
+            Lwt.return_unit
          )
     )
     (fun ex ->
@@ -40,7 +39,7 @@ let transmit_ipv4 packet iface =
                    (Printexc.to_string ex)
                    Nat_packet.pp packet
                );
-       Lwt.return ()
+       Lwt.return_unit
     )
 
 let forward_ipv4 t packet =
@@ -127,19 +126,19 @@ let add_nat_and_forward_ipv4 t packet =
   | Ok packet -> forward_ipv4 t packet
   | Error e ->
     Log.warn (fun f -> f "Failed to add NAT rewrite rule: %s (%a)" e pp_header packet);
-    Lwt.return ()
+    Lwt.return_unit
 
 (* Add a NAT rule to redirect this conversation to [host:port] instead of us. *)
 let nat_to t ~host ~port packet =
   match Router.resolve t host with
-  | Ipaddr.V6 _ -> Log.warn (fun f -> f "Cannot NAT with IPv6"); Lwt.return ()
+  | Ipaddr.V6 _ -> Log.warn (fun f -> f "Cannot NAT with IPv6"); Lwt.return_unit
   | Ipaddr.V4 target ->
     let xl_host = t.Router.uplink#my_ip in
     My_nat.add_nat_rule_and_translate t.Router.nat ~xl_host (`Redirect (target, port)) packet >>= function
     | Ok packet -> forward_ipv4 t packet
     | Error e ->
       Log.warn (fun f -> f "Failed to add NAT redirect rule: %s (%a)" e pp_header packet);
-      Lwt.return ()
+      Lwt.return_unit
 
 (* Handle incoming packets *)
 
@@ -150,12 +149,12 @@ let apply_rules t rules ~dst info =
   | `Accept, (`External _ | `NetVM) -> transmit_ipv4 packet t.Router.uplink
   | `Accept, `Firewall ->
       Log.warn (fun f -> f "Bad rule: firewall can't accept packets %a" (pp_packet t) info);
-      return ()
+      Lwt.return_unit
   | `NAT, _ -> add_nat_and_forward_ipv4 t packet
   | `NAT_to (host, port), _ -> nat_to t packet ~host ~port
   | `Drop reason, _ ->
       Log.info (fun f -> f "Dropped packet (%s) %a" reason (pp_packet t) info);
-      return ()
+      Lwt.return_unit
 
 let handle_low_memory t =
   match Memory_pressure.status () with
@@ -167,7 +166,7 @@ let handle_low_memory t =
 
 let ipv4_from_client t ~src packet =
   handle_low_memory t >>= function
-  | `Memory_critical -> return ()
+  | `Memory_critical -> Lwt.return_unit
   | `Ok ->
   (* Check for existing NAT entry for this packet *)
   translate t packet >>= function
@@ -177,23 +176,23 @@ let ipv4_from_client t ~src packet =
   let `IPv4 (ip, _transport) = packet in
   let dst = Router.classify t (Ipaddr.V4 ip.Ipv4_packet.dst) in
   match classify ~src:(resolve_client src) ~dst:(resolve_host dst) packet with
-  | None -> return ()
+  | None -> Lwt.return_unit
   | Some info -> apply_rules t Rules.from_client ~dst info
 
 let ipv4_from_netvm t packet =
   handle_low_memory t >>= function
-  | `Memory_critical -> return ()
+  | `Memory_critical -> Lwt.return_unit
   | `Ok ->
   let `IPv4 (ip, _transport) = packet in
   let src = Router.classify t (Ipaddr.V4 ip.Ipv4_packet.src) in
   let dst = Router.classify t (Ipaddr.V4 ip.Ipv4_packet.dst) in
   match classify ~src ~dst:(resolve_host dst) packet with
-  | None -> return ()
+  | None -> Lwt.return_unit
   | Some info ->
   match src with
   | `Client _ | `Firewall ->
     Log.warn (fun f -> f "Frame from NetVM has internal source IP address! %a" (pp_packet t) info);
-    return ()
+    Lwt.return_unit
   | `External _ | `NetVM as src ->
   translate t packet >>= function
   | Some frame -> forward_ipv4 t frame

fw_utils.ml

@@ -41,9 +41,6 @@ let error fmt =
   let err s = Failure s in
   Printf.ksprintf err fmt
 
-let return = Lwt.return
-let fail = Lwt.fail
-
 let or_raise msg pp = function
   | Ok x -> x
   | Error e -> failwith (Fmt.strf "%s: %a" msg pp e)

unikernel.ml

@@ -46,7 +46,7 @@ module Main (Clock : Mirage_clock_lwt.MCLOCK) = struct
         (fun `Cant_happen -> assert false)
         (fun ex ->
           Log.warn (fun f -> f "GUI thread failed: %s" (Printexc.to_string ex));
-          return ()
+          Lwt.return_unit
         )
     )
 
@@ -70,7 +70,7 @@ module Main (Clock : Mirage_clock_lwt.MCLOCK) = struct
     (* Watch for shutdown requests from Qubes *)
     let shutdown_rq =
       OS.Lifecycle.await_shutdown_request () >>= fun (`Poweroff | `Reboot) ->
-      return () in
+      Lwt.return_unit in
     (* Set up networking *)
     let max_entries = Key_gen.nat_table_size () in
     My_nat.create ~max_entries >>= fun nat ->

uplink.ml

@@ -46,12 +46,12 @@ module Make(Clock : Mirage_clock_lwt.MCLOCK) = struct
                 Lwt.return_unit
               | Error e ->
                 Log.warn (fun f -> f "Ignored unknown IPv4 message from uplink: %a" Nat_packet.pp_error e);
-                Lwt.return ()
+                Lwt.return_unit
               | Ok None -> Lwt.return_unit
               | Ok (Some packet) ->
                 Firewall.ipv4_from_netvm router packet
             )
-          ~ipv6:(fun _ip -> return ())
+          ~ipv6:(fun _ip -> Lwt.return_unit)
           frame
       ) >|= or_raise "Uplink listen loop" Netif.pp_error
 
@@ -70,5 +70,5 @@ module Make(Clock : Mirage_clock_lwt.MCLOCK) = struct
       ~my_ip:ip
       ~other_ip:config.Dao.uplink_netvm_ip in
     let fragments = Fragments.Cache.create (256 * 1024) in
-    return { net; eth; arp; interface ; fragments }
+    Lwt.return { net; eth; arp; interface ; fragments }
 end