From 3daae22a68a6e74c99d39a8c6b628f5c9121c54a Mon Sep 17 00:00:00 2001
From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Thu, 17 May 2012 23:14:26 -0400
Subject: [PATCH] Update return value of "set" operations

To follow the way the Linux kernel implements atomic_set(), we change
some API functions so they don't return any value anymore.

This is now the case for:

uatomic_set()
rcu_set_pointer()
rcu_assign_pointer()

This API change is very minor. In all instances of the Linux kernel
using rcu_assign_pointer(), none currently care about its return value.

However, we keep ABI compatibility: rcu_set_pointer_sym() still returns
the "v" value, even though it is not used by its wrapper macro anymore.

Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
---
 urcu-pointer.h             | 22 +++++++++++++---------
 urcu/static/urcu-pointer.h |  4 ++--
 urcu/uatomic/generic.h     |  2 +-
 3 files changed, 16 insertions(+), 12 deletions(-)

diff --git a/urcu-pointer.h b/urcu-pointer.h
index dd64ec4..1e1e6bf 100644
--- a/urcu-pointer.h
+++ b/urcu-pointer.h
@@ -47,9 +47,9 @@ extern "C" {
 #define rcu_dereference		_rcu_dereference
 
 /*
- * rcu_cmpxchg_pointer(type **ptr, type *new, type *old)
+ * type *rcu_cmpxchg_pointer(type **ptr, type *new, type *old)
  * type *rcu_xchg_pointer(type **ptr, type *new)
- * type *rcu_set_pointer(type **ptr, type *new)
+ * void rcu_set_pointer(type **ptr, type *new)
  *
  * RCU pointer updates.
  * @ptr: address of the pointer to modify
@@ -94,20 +94,24 @@ extern void *rcu_xchg_pointer_sym(void **p, void *v);
 		(_________p1);						     \
 	})
 
+/*
+ * Note: rcu_set_pointer_sym returns @v because we don't want to break
+ * the ABI. At the API level, rcu_set_pointer() now returns void. Use of
+ * the return value is therefore deprecated, and will cause a build
+ * error.
+ */
 extern void *rcu_set_pointer_sym(void **p, void *v);
 #define rcu_set_pointer(p, v)						     \
-	({								     \
+	do {								     \
 		typeof(*(p)) _________pv = (v);			             \
-		typeof(*(p)) _________p1 = URCU_FORCE_CAST(typeof(*(p)),     \
-			rcu_set_pointer_sym(URCU_FORCE_CAST(void **, p),     \
-					    _________pv));		     \
-		(_________p1);						     \
-	})
+		(void) rcu_set_pointer_sym(URCU_FORCE_CAST(void **, p),	     \
+					    _________pv);		     \
+	} while (0)
 
 #endif /* !_LGPL_SOURCE */
 
 /*
- * rcu_assign_pointer(type *ptr, type *new)
+ * void rcu_assign_pointer(type *ptr, type *new)
  *
  * Same as rcu_set_pointer, but takes the pointer to assign to rather than its
  * address as first parameter. Provided for compatibility with the Linux kernel
diff --git a/urcu/static/urcu-pointer.h b/urcu/static/urcu-pointer.h
index acd7cee..906caa0 100644
--- a/urcu/static/urcu-pointer.h
+++ b/urcu/static/urcu-pointer.h
@@ -102,13 +102,13 @@ extern "C" {
 
 
 #define _rcu_set_pointer(p, v)				\
-	({						\
+	do {						\
 		typeof(*p) _________pv = (v);		\
 		if (!__builtin_constant_p(v) || 	\
 		    ((v) != NULL))			\
 			cmm_wmb();				\
 		uatomic_set(p, _________pv);		\
-	})
+	} while (0)
 
 /**
  * _rcu_assign_pointer - assign (publicize) a pointer to a new data structure
diff --git a/urcu/uatomic/generic.h b/urcu/uatomic/generic.h
index bfd9b68..9e2e780 100644
--- a/urcu/uatomic/generic.h
+++ b/urcu/uatomic/generic.h
@@ -29,7 +29,7 @@ extern "C" {
 #endif
 
 #ifndef uatomic_set
-#define uatomic_set(addr, v)	CMM_STORE_SHARED(*(addr), (v))
+#define uatomic_set(addr, v)	((void) CMM_STORE_SHARED(*(addr), (v)))
 #endif
 
 #ifndef uatomic_read
-- 
2.34.1