[xen master] tools/ocaml/evtchn: OCaml 5 support, fix potential resource leak

[patchbot@xxxxxxx]

commit 22d5affdf0cecfa6faae46fbaec68b8018835220
Author:     Edwin Török <edvin.torok@xxxxxxxxxx>
AuthorDate: Tue Jan 18 15:04:48 2022 +0000
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Thu Dec 1 16:07:17 2022 +0000

    tools/ocaml/evtchn: OCaml 5 support, fix potential resource leak
    
    There is no binding for xenevtchn_close().  In principle, this is a resource
    leak, but the typical usage is as a singleton that lives for the lifetime of
    the program.
    
    Ocaml 5 no longer permits storing a naked C pointer in an Ocaml value.
    
    Therefore, use a Custom block.  This allows us to use the finaliser callback
    to call xenevtchn_close(), if the Ocaml object goes out of scope.
    
    Signed-off-by: Edwin Török <edvin.torok@xxxxxxxxxx>
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Acked-by: Christian Lindig <christian.lindig@xxxxxxxxxx>
---
 tools/ocaml/libs/eventchn/xeneventchn_stubs.c | 21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/tools/ocaml/libs/eventchn/xeneventchn_stubs.c 
b/tools/ocaml/libs/eventchn/xeneventchn_stubs.c
index f889a7a2e4..37f1cc4e14 100644
--- a/tools/ocaml/libs/eventchn/xeneventchn_stubs.c
+++ b/tools/ocaml/libs/eventchn/xeneventchn_stubs.c
@@ -33,7 +33,22 @@
 #include <caml/fail.h>
 #include <caml/signals.h>
 
-#define _H(__h) ((xenevtchn_handle *)(__h))
+#define _H(__h) (*((xenevtchn_handle **)Data_custom_val(__h)))
+
+static void stub_evtchn_finalize(value v)
+{
+       xenevtchn_close(_H(v));
+}
+
+static struct custom_operations xenevtchn_ops = {
+       .identifier  = "xenevtchn",
+       .finalize    = stub_evtchn_finalize,
+       .compare     = custom_compare_default,     /* Can't compare     */
+       .hash        = custom_hash_default,        /* Can't hash        */
+       .serialize   = custom_serialize_default,   /* Can't serialize   */
+       .deserialize = custom_deserialize_default, /* Can't deserialize */
+       .compare_ext = custom_compare_ext_default, /* Can't compare     */
+};
 
 CAMLprim value stub_eventchn_init(void)
 {
@@ -48,7 +63,9 @@ CAMLprim value stub_eventchn_init(void)
        if (xce == NULL)
                caml_failwith("open failed");
 
-       result = (value)xce;
+       result = caml_alloc_custom(&xenevtchn_ops, sizeof(xce), 0, 1);
+       _H(result) = xce;
+
        CAMLreturn(result);
 }
 
--
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