[Xen-changelog] [xen-unstable] libxl: provide STATE_AO_GC

[Xen patchbot-unstable <patchbot@xxxxxxx>]

# HG changeset patch
# User Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
# Date 1334150058 -3600
# Node ID d196634484a9f86136704f973293925445961079
# Parent  8a88f6e209dbecfeb0426970540df22351f74fe4
libxl: provide STATE_AO_GC

Provide a convenience macro for use in ao callback functions, and
document that it should be used.

Signed-off-by: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
Committed-by: Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
---


diff -r 8a88f6e209db -r d196634484a9 tools/libxl/libxl_internal.h
--- a/tools/libxl/libxl_internal.h      Wed Apr 11 14:14:18 2012 +0100
+++ b/tools/libxl/libxl_internal.h      Wed Apr 11 14:14:18 2012 +0100
@@ -1266,9 +1266,10 @@ _hidden void libxl__egc_cleanup(libxl__e
  * - Note that during callback functions, two gcs are available:
  *    - The one in egc, whose lifetime is only this callback
  *    - The one in ao, whose lifetime is the asynchronous operation
- *   Usually callback function should use CONTAINER_OF
- *   to obtain its own structure, containing a pointer to the ao,
- *   and then use the gc from that ao.
+ *   Usually callback function should use CONTAINER_OF to obtain its
+ *   own state structure, containing a pointer to the ao.  It should
+ *   then obtain the ao and use the ao's gc; this is most easily done
+ *   using the convenience macro STATE_AO_GC.
  */
 
 #define AO_CREATE(ctx, domid, ao_how)                           \
@@ -1298,6 +1299,10 @@ _hidden void libxl__egc_cleanup(libxl__e
 #define AO_GC                                   \
     libxl__gc *const gc = &ao->gc
 
+#define STATE_AO_GC(op_ao)                      \
+    libxl__ao *const ao = (op_ao);              \
+    AO_GC
+
 
 /* All of these MUST be called with the ctx locked.
  * libxl__ao_inprogress MUST be called with the ctx locked exactly once. */

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