tools/ocaml/evtchn: Add binding for xenevtchn_fdopen()

For live update, the new oxenstored needs to reconstruct an evtchn object
around an existing file descriptor.

Signed-off-by: Edwin Török <edvin.torok@citrix.com>
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Christian Lindig <christian.lindig@citrix.com>
(cherry picked from commit 7ba68a6c55)

tools/ocaml/libs/eventchn/xeneventchn.ml

@@ -17,6 +17,7 @@
 type handle
 
 external init: unit -> handle = "stub_eventchn_init"
+external fdopen: Unix.file_descr -> handle = "stub_eventchn_fdopen"
 external fd: handle -> Unix.file_descr = "stub_eventchn_fd"
 
 type t = int

tools/ocaml/libs/eventchn/xeneventchn.mli

@@ -47,6 +47,10 @@ val init: unit -> handle
 (** Return an initialised event channel interface. On error it
     will throw a Failure exception. *)
 
+val fdopen: Unix.file_descr -> handle
+(** Return an initialised event channel interface, from an already open evtchn
+    file descriptor.  On error it will throw a Failure exception. *)
+
 val fd: handle -> Unix.file_descr
 (** Return a file descriptor suitable for Unix.select. When
     the descriptor becomes readable, it is safe to call 'pending'.

tools/ocaml/libs/eventchn/xeneventchn_stubs.c

@@ -69,6 +69,25 @@ CAMLprim value stub_eventchn_init(void)
 	CAMLreturn(result);
 }
 
+CAMLprim value stub_eventchn_fdopen(value fdval)
+{
+	CAMLparam1(fdval);
+	CAMLlocal1(result);
+	xenevtchn_handle *xce;
+
+	caml_enter_blocking_section();
+	xce = xenevtchn_fdopen(NULL, Int_val(fdval), 0);
+	caml_leave_blocking_section();
+
+	if (xce == NULL)
+		caml_failwith("evtchn fdopen failed");
+
+	result = caml_alloc_custom(&xenevtchn_ops, sizeof(xce), 0, 1);
+	_H(result) = xce;
+
+	CAMLreturn(result);
+}
+
 CAMLprim value stub_eventchn_fd(value xce)
 {
 	CAMLparam1(xce);