[Xen-devel] [PATCH] libxl: unconst the event argument to the event_occurs hook.

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

The event is supposed to become owned, and therefore freed, by the application
and the const prevents this.

Unfortunately there is no way to remove the const without breaking existing
callers. The best we can do is use the LIBXL_API_VERSION provisions to remove
the const for callers who wish only to support the 4.3 API and newer.

Callers who wish to support 4.2 will need to live with casting away the const.

Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
Cc: Ian.Jackson@xxxxxxxxxx
Cc: George.Dunlap@xxxxxxxxx
Cc: Jim Fehlig <jfehlig@xxxxxxxx>
Cc: Rob Hoes <Rob.Hoes@xxxxxxxxxx>
---
 tools/libxl/libxl.h       |   14 ++++++++++++--
 tools/libxl/libxl_event.h |    6 +++++-
 2 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/tools/libxl/libxl.h b/tools/libxl/libxl.h
index 25efa76..ef96bce 100644
--- a/tools/libxl/libxl.h
+++ b/tools/libxl/libxl.h
@@ -273,9 +273,9 @@
 #include <libxl_uuid.h>
 #include <_libxl_list.h>
 
-/* API compatibility. Only 0x040200 is supported at this time. */
+/* API compatibility. */
 #ifdef LIBXL_API_VERSION
-#if LIBXL_API_VERSION != 0x040200
+#if LIBXL_API_VERSION != 0x040200 && LIBXL_API_VERSION != 0x040300
 #error Unknown LIBXL_API_VERSION
 #endif
 #endif
@@ -308,6 +308,16 @@
  */
 #define LIBXL_HAVE_DEVICE_BACKEND_DOMNAME 1
 
+/*
+ * LIBXL_HAVE_NONCONST_EVENT_OCCURS_EVENT_ARG
+ *
+ * This argument was erroneously "const" in the 4.2 release despite
+ * the requirement for the callback to free the event.
+ */
+#if LIBXL_API_VERSION != 0x040200
+#define LIBXL_HAVE_NONCONST_EVENT_OCCURS_EVENT_ARG 1
+#endif
+
 /* Functions annotated with LIBXL_EXTERNAL_CALLERS_ONLY may not be
  * called from within libxl itself. Callers outside libxl, who
  * do not #include libxl_internal.h, are fine. */
diff --git a/tools/libxl/libxl_event.h b/tools/libxl/libxl_event.h
index 51f2721..27a65dc 100644
--- a/tools/libxl/libxl_event.h
+++ b/tools/libxl/libxl_event.h
@@ -64,7 +64,11 @@ void libxl_event_free(libxl_ctx *ctx, libxl_event *event);
 
 typedef struct libxl_event_hooks {
     uint64_t event_occurs_mask;
-    void (*event_occurs)(void *user, const libxl_event *event);
+    void (*event_occurs)(void *user,
+#ifndef LIBXL_HAVE_NONCONST_EVENT_OCCURS_EVENT_ARG
+                         const
+#endif
+                         libxl_event *event);
     void (*disaster)(void *user, libxl_event_type type,
                      const char *msg, int errnoval);
 } libxl_event_hooks;
-- 
1.7.2.5


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