ocaml: eventchn: add a 'type t' to represent an event channel

It's a common OCaml convention to add a 'type t' in a module to
represent the main "thing" that the module is about. We add an
opaque type t and to_int/of_int functions for those who really
need it, in particular:

  1. to_int is needed for debug logging; and
  2. both to_int and of_int are needed for anyone who communicates
     a port number through xenstore.

Signed-off-by: David Scott <dave.scott@eu.citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>

tools/ocaml/libs/eventchn/xeneventchn.ml

@@ -20,6 +20,9 @@ type handle
 
 external init: unit -> handle = "stub_eventchn_init"
 external fd: handle -> Unix.file_descr = "stub_eventchn_fd"
+
+type t = int
+
 external notify: handle -> int -> unit = "stub_eventchn_notify"
 external bind_interdomain: handle -> int -> int -> int = "stub_eventchn_bind_interdomain"
 external bind_dom_exc_virq: handle -> int = "stub_eventchn_bind_dom_exc_virq"
@@ -27,4 +30,7 @@ external unbind: handle -> int -> unit = "stub_eventchn_unbind"
 external pending: handle -> int = "stub_eventchn_pending"
 external unmask: handle -> int -> unit = "stub_eventchn_unmask"
 
+let to_int x = x
+let of_int x = x
+
 let _ = Callback.register_exception "eventchn.error" (Error "register_callback")

tools/ocaml/libs/eventchn/xeneventchn.mli

@@ -18,14 +18,19 @@ exception Error of string
 
 type handle
 
+type t
+
+val to_int: t -> int
+val of_int: int -> t
+
 external init : unit -> handle = "stub_eventchn_init"
 external fd: handle -> Unix.file_descr = "stub_eventchn_fd"
 
-external notify : handle -> int -> unit = "stub_eventchn_notify"
-external bind_interdomain : handle -> int -> int -> int
+external notify : handle -> t -> unit = "stub_eventchn_notify"
+external bind_interdomain : handle -> int -> int -> t
   = "stub_eventchn_bind_interdomain"
-external bind_dom_exc_virq : handle -> int = "stub_eventchn_bind_dom_exc_virq"
-external unbind : handle -> int -> unit = "stub_eventchn_unbind"
-external pending : handle -> int = "stub_eventchn_pending"
-external unmask : handle -> int -> unit
+external bind_dom_exc_virq : handle -> t = "stub_eventchn_bind_dom_exc_virq"
+external unbind : handle -> t -> unit = "stub_eventchn_unbind"
+external pending : handle -> t = "stub_eventchn_pending"
+external unmask : handle -> t -> unit
   = "stub_eventchn_unmask"

tools/ocaml/xenstored/domain.ml

@@ -17,6 +17,7 @@
 open Printf
 
 let debug fmt = Logging.debug "domain" fmt
+let warn  fmt = Logging.warn  "domain" fmt
 
 type t =
 {
@@ -25,7 +26,7 @@ type t =
 	remote_port: int;
 	interface: Xenmmap.mmap_interface;
 	eventchn: Event.t;
-	mutable port: int;
+	mutable port: Xeneventchn.t option;
 }
 
 let get_path dom = "/local/domain/" ^ (sprintf "%u" dom.id)
@@ -34,19 +35,30 @@ let get_interface d = d.interface
 let get_mfn d = d.mfn
 let get_remote_port d = d.remote_port
 
-let dump d chan =
-	fprintf chan "dom,%d,%nd,%d\n" d.id d.mfn d.port
+let string_of_port = function
+| None -> "None"
+| Some x -> string_of_int (Xeneventchn.to_int x)
 
-let notify dom = Event.notify dom.eventchn dom.port; ()
+let dump d chan =
+	fprintf chan "dom,%d,%nd,%s\n" d.id d.mfn (string_of_port d.port)
+
+let notify dom = match dom.port with
+| None ->
+	warn "domain %d: attempt to notify on unknown port" dom.id
+| Some port ->
+	Event.notify dom.eventchn port
 
 let bind_interdomain dom =
-	dom.port <- Event.bind_interdomain dom.eventchn dom.id dom.remote_port;
-	debug "domain %d bound port %d" dom.id dom.port
+	dom.port <- Some (Event.bind_interdomain dom.eventchn dom.id dom.remote_port);
+	debug "domain %d bound port %s" dom.id (string_of_port dom.port)
 
 
 let close dom =
-	debug "domain %d unbound port %d" dom.id dom.port;
-	Event.unbind dom.eventchn dom.port;
+	debug "domain %d unbound port %s" dom.id (string_of_port dom.port);
+	begin match dom.port with
+	| None -> ()
+	| Some port -> Event.unbind dom.eventchn port
+	end;
 	Xenmmap.unmap dom.interface;
 	()
 
@@ -56,7 +68,7 @@ let make id mfn remote_port interface eventchn = {
 	remote_port = remote_port;
 	interface = interface;
 	eventchn = eventchn;
-	port = -1
+	port = None
 }
 
 let is_dom0 d = d.id = 0

tools/ocaml/xenstored/event.ml

@@ -17,12 +17,12 @@
 (**************** high level binding ****************)
 type t = {
 	handle: Xeneventchn.handle;
-	mutable virq_port: int;
+	mutable virq_port: Xeneventchn.t option;
 }
 
-let init () = { handle = Xeneventchn.init (); virq_port = -1; }
+let init () = { handle = Xeneventchn.init (); virq_port = None; }
 let fd eventchn = Xeneventchn.fd eventchn.handle
-let bind_dom_exc_virq eventchn = eventchn.virq_port <- Xeneventchn.bind_dom_exc_virq eventchn.handle
+let bind_dom_exc_virq eventchn = eventchn.virq_port <- Some (Xeneventchn.bind_dom_exc_virq eventchn.handle)
 let bind_interdomain eventchn domid port = Xeneventchn.bind_interdomain eventchn.handle domid port
 let unbind eventchn port = Xeneventchn.unbind eventchn.handle port
 let notify eventchn port = Xeneventchn.notify eventchn.handle port

tools/ocaml/xenstored/xenstored.ml

@@ -300,7 +300,7 @@ let _ =
 		and handle_eventchn fd =
 			let port = Event.pending eventchn in
 			finally (fun () ->
-				if port = eventchn.Event.virq_port then (
+				if Some port = eventchn.Event.virq_port then (
 					let (notify, deaddom) = Domains.cleanup xc domains in
 					List.iter (Connections.del_domain cons) deaddom;
 					if deaddom <> [] || notify then