[Xen-devel] [PATCH v2] libxl: Fix incorrect return of OSEVENT_HOOK macro

[Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>]

On 05/09/2012 09:19 AM, Ian Jackson wrote:
> Daniel De Graaf writes ("[PATCH] libxl: Fix incorrect return of OSEVENT_HOOK 
> macro"):
>> The OSEVENT_HOOK_INTERN macro incorrectly returned the value of the
>> expression CTX->osevent_in_hook-- (usually 1) instead of the value of
>> the function call it made. Change the macro to a statement including the
>> return variable to fix this.
> 
> Well spotted, thanks.  But I think it would be better to use the GCC
> statement expression syntax to avoid changing the call sites ?
> 
> Ian.
> 

Agreed, using the statement expression syntax seems cleaner here.

------8<------------------------------

The OSEVENT_HOOK_INTERN macro incorrectly returned the value of the
expression CTX->osevent_in_hook-- (usually 1) instead of the value of
the function call it made. Fix the macro to return the proper value.

Signed-off-by: Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>
---
 tools/libxl/libxl_event.c |   31 +++++++++++++++++++------------
 1 files changed, 19 insertions(+), 12 deletions(-)

diff --git a/tools/libxl/libxl_event.c b/tools/libxl/libxl_event.c
index 638b9ab..bee0e27 100644
--- a/tools/libxl/libxl_event.c
+++ b/tools/libxl/libxl_event.c
@@ -27,18 +27,25 @@
  * these macros, with the ctx locked.  Likewise all the "occurred"
  * entrypoints from the application should assert(!in_hook);
  */
-#define OSEVENT_HOOK_INTERN(defval, hookname, ...)                      \
-    (CTX->osevent_hooks                                                 \
-     ? (CTX->osevent_in_hook++,                                         \
-        CTX->osevent_hooks->hookname(CTX->osevent_user, __VA_ARGS__),   \
-        CTX->osevent_in_hook--)                                         \
-     : defval)
-
-#define OSEVENT_HOOK(hookname,...)                      \
-    OSEVENT_HOOK_INTERN(0, hookname, __VA_ARGS__)
-
-#define OSEVENT_HOOK_VOID(hookname,...)                 \
-    OSEVENT_HOOK_INTERN((void)0, hookname, __VA_ARGS__)
+#define OSEVENT_HOOK(hookname,...) ({                                       \
+    int rc;                                                                 \
+    if (CTX->osevent_hooks) {                                               \
+        CTX->osevent_in_hook++;                                             \
+        rc = CTX->osevent_hooks->hookname(CTX->osevent_user, __VA_ARGS__);  \
+        CTX->osevent_in_hook--;                                             \
+    } else {                                                                \
+        rc = 0;                                                             \
+    }                                                                       \
+    rc;                                                                     \
+})
+
+#define OSEVENT_HOOK_VOID(hookname,...) do {                                \
+    if (CTX->osevent_hooks) {                                               \
+        CTX->osevent_in_hook++;                                             \
+        CTX->osevent_hooks->hookname(CTX->osevent_user, __VA_ARGS__);       \
+        CTX->osevent_in_hook--;                                             \
+    }                                                                       \
+} while (0)
 
 /*
  * fd events


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