From: Simon Wilkinson <sxw@your-file-system.com>
Date: Sat, 22 Oct 2011 08:45:10 +0000 (+0100)
Subject: opr: Add opr_containerof
X-Git-Tag: upstream/1.8.0_pre1^2~3053
X-Git-Url: https://git.michaelhowe.org/gitweb/?a=commitdiff_plain;h=1a056d24a79242db09963dd0b0c2193c5034b61b;p=packages%2Fo%2Fopenafs.git

opr: Add opr_containerof

Add the opr_containerof macro, which can be used to find the base
address of a structure which contains a member whose location is known.

This formulation is heavily used throughout OpenAFS to determine the
base address of structures containing queue pointers - this provides
a central definition, rather than coding it from scratch each time.

Change-Id: I2a32a214252ad304238f740ad92579e5bb7287be
Reviewed-on: http://gerrit.openafs.org/5836
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementix.org>
---

diff --git a/src/opr/opr.h b/src/opr/opr.h
index b53211c2a..d7db2cc02 100644
--- a/src/opr/opr.h
+++ b/src/opr/opr.h
@@ -1,7 +1,13 @@
 #ifndef OPENAFS_OPR_OPR_H
 #define OPENAFS_OPR_OPR_H 1
 
+/* macros */
+
+#define opr_containerof(ptr, structure, member) \
+   ((structure *)((char *)(ptr)-(char *)(&((structure *)NULL)->member)))
+
 /* assert.c */
+
 #ifdef AFS_NT40_ENV
 # define opr_abort() opr_NTAbort()
 extern void opr_NTAbort(void);