linux-kernel - [PATCH tip/core/rcu 04/14] rcu: Add a gcc-style structure initializer for RCU pointers

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Message-Id: <1339791195-26389-4-git-send-email-paulmck@linux.vnet.ibm.com>
Date:	Fri, 15 Jun 2012 13:13:05 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	mingo@...e.hu, laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...ymtl.ca,
	josh@...htriplett.org, niv@...ibm.com, tglx@...utronix.de,
	peterz@...radead.org, rostedt@...dmis.org, Valdis.Kletnieks@...edu,
	dhowells@...hat.com, eric.dumazet@...il.com, darren@...art.com,
	fweisbec@...il.com, patches@...aro.org,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 04/14] rcu: Add a gcc-style structure initializer for RCU pointers

From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>

RCU_INIT_POINTER() returns a value that is never used, and which should
be abolished due to terminal ugliness:

	q = RCU_INIT_POINTER(global_p, p);

However, there are two uses that cannot be handled by a do-while
formulation because they do gcc-style initialization:

	RCU_INIT_POINTER(.real_cred, &init_cred),
	RCU_INIT_POINTER(.cred, &init_cred),

This usage is clever, but not necessarily the nicest approach.  This
commit therefore creates an INIT_RCU_POINTER() macro that is specifically
designed for gcc-style initialization.

Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
 include/linux/rcupdate.h |    8 ++++++++
 1 files changed, 8 insertions(+), 0 deletions(-)

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 26d1a47..eb92c21 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -906,6 +906,14 @@ static inline notrace void rcu_read_unlock_sched_notrace(void)
 #define RCU_INIT_POINTER(p, v) \
 		p = (typeof(*v) __force __rcu *)(v)
 
+/**
+ * INIT_RCU_POINTER() - statically initialize an RCU protected pointer
+ *
+ * GCC-style initialization for an RCU-protected pointer in a structure field.
+ */
+#define INIT_RCU_POINTER(p, v) \
+		.p = (typeof(*v) __force __rcu *)(v)
+
 static __always_inline bool __is_kfree_rcu_offset(unsigned long offset)
 {
 	return offset < 4096;
-- 
1.7.8

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