tools/ocaml/evtchn: Extend the init() binding with a cloexec flag

For live update, oxenstored wants to clear CLOEXEC on the evtchn handle, so it
survives the execve() into the new oxenstored.

Have the new interface match how cloexec works in other Ocaml standard
libraries.

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 9bafe4a533)

tools/ocaml/libs/eventchn/xeneventchn.ml

@@ -16,7 +16,10 @@
 
 type handle
 
-external init: unit -> handle = "stub_eventchn_init"
+external _init: bool -> handle = "stub_eventchn_init"
+
+let init ?(cloexec=true) () = _init cloexec
+
 external fdopen: Unix.file_descr -> handle = "stub_eventchn_fdopen"
 external fd: handle -> Unix.file_descr = "stub_eventchn_fd"
 

tools/ocaml/libs/eventchn/xeneventchn.mli

@@ -43,9 +43,12 @@ val to_int: t -> int
 
 val of_int: int -> t
 
-val init: unit -> handle
-(** Return an initialised event channel interface. On error it
-    will throw a Failure exception. *)
+val init: ?cloexec:bool -> unit -> handle
+(** [init ?cloexec ()]
+    Return an initialised event channel interface.
+    The default is to close the underlying file descriptor
+    on [execve], which can be overriden with [~cloexec:false].
+    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

tools/ocaml/libs/eventchn/xeneventchn_stubs.c

@@ -50,14 +50,18 @@ static struct custom_operations xenevtchn_ops = {
 	.compare_ext = custom_compare_ext_default, /* Can't compare     */
 };
 
-CAMLprim value stub_eventchn_init(void)
+CAMLprim value stub_eventchn_init(value cloexec)
 {
-	CAMLparam0();
+	CAMLparam1(cloexec);
 	CAMLlocal1(result);
 	xenevtchn_handle *xce;
+	unsigned int flags = 0;
+
+	if ( !Bool_val(cloexec) )
+		flags |= XENEVTCHN_NO_CLOEXEC;
 
 	caml_enter_blocking_section();
-	xce = xenevtchn_open(NULL, 0);
+	xce = xenevtchn_open(NULL, flags);
 	caml_leave_blocking_section();
 
 	if (xce == NULL)