tools/ocaml: Factor out compatiblity handling

... rather than having each library implement its own subset.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Christian Lindig <christian.lindig@cloud.com>

tools/ocaml/libs/xc/Makefile

@@ -2,7 +2,7 @@ OCAML_TOPLEVEL=$(CURDIR)/../..
 XEN_ROOT=$(OCAML_TOPLEVEL)/../..
 include $(OCAML_TOPLEVEL)/common.make
 
-CFLAGS += -I../mmap $(CFLAGS_libxenctrl) $(CFLAGS_libxenguest)
+CFLAGS += -I../ -I../mmap $(CFLAGS_libxenctrl) $(CFLAGS_libxenguest)
 CFLAGS += $(APPEND_CFLAGS)
 OCAMLINCLUDE += -I ../mmap -I ../eventchn
 

tools/ocaml/libs/xc/xenctrl_stubs.c

@@ -25,6 +25,8 @@
 #include <caml/fail.h>
 #include <caml/callback.h>
 
+#include "xen-caml-compat.h"
+
 #include <sys/mman.h>
 #include <stdint.h>
 #include <string.h>
@@ -37,14 +39,6 @@
 
 #include "mmap_stubs.h"
 
-#ifndef Val_none
-#define Val_none (Val_int(0))
-#endif
-
-#ifndef Tag_some
-#define Tag_some 0
-#endif
-
 static inline xc_interface *xch_of_val(value v)
 {
 	xc_interface *xch = *(xc_interface **)Data_custom_val(v);
@@ -744,8 +738,7 @@ CAMLprim value stub_xc_evtchn_status(value xch_val, value domid, value port)
 	Store_field(result_status, 0, Val_int(status.vcpu));
 	Store_field(result_status, 1, stat);
 
-	result = caml_alloc_small(1, Tag_some);
-	Store_field(result, 0, result_status);
+	result = caml_alloc_some(result_status);
 
 	CAMLreturn(result);
 }

tools/ocaml/libs/xen-caml-compat.h

@@ -0,0 +1,23 @@
+/* SPDX-License-Identifier: LGPL-2.1-only WITH OCaml-LGPL-linking-exception */
+#ifndef XEN_CAML_COMPAT_H
+#define XEN_CAML_COMPAT_H
+
+#ifndef Val_none /* Option handling.  Compat for Ocaml < 4.12 */
+
+#define Val_none Val_int(0)
+#define Tag_some 0
+#define Some_val(v) Field(v, 0)
+
+static inline value caml_alloc_some(value v)
+{
+    CAMLparam1(v);
+
+    value some = caml_alloc_small(1, Tag_some);
+    Field(some, 0) = v;
+
+    CAMLreturn(some);
+}
+
+#endif /* !Val_none */
+
+#endif /* XEN_CAML_COMPAT_H */