linux-kernel - [PATCH 1/3] core: New macro to execute code only once

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Date:	Tue, 15 Oct 2013 22:50:50 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Liu Chuansheng <chuansheng.liu@...el.com>,
	Ingo Molnar <mingo@...nel.org>
Subject: [PATCH 1/3] core: New macro to execute code only once

Introduce DO_COND(), DO_ONCE() and DO_ONCE_COND(). These
macros should ease the consolidation of CPP code when
it is deemed to be executed only once and/or after a
condition is verified. This incluse printk_once, WARN_ON,
WARN_ON_ONCE, etc...

Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Liu Chuansheng <chuansheng.liu@...el.com>
Cc: Ingo Molnar <mingo@...nel.org>
---
 include/linux/once.h | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)
 create mode 100644 include/linux/once.h

diff --git a/include/linux/once.h b/include/linux/once.h
new file mode 100644
index 0000000..9399f37
--- /dev/null
+++ b/include/linux/once.h
@@ -0,0 +1,26 @@
+#ifndef _LINUX_ONCE_H
+#define _LINUX_ONCE_H
+
+#include <linux/compiler.h>
+
+#define DO_COND(condition, to_do) ({		\
+	int __ret = !!(condition);		\
+	if (unlikely(__ret)) {			\
+		to_do;				\
+	}					\
+	unlikely(__ret);			\
+})
+
+#define DO_ONCE(to_do) ({			\
+	static bool __done;			\
+						\
+	if (!__done) {				\
+		__done = true;			\
+		to_do;				\
+	}					\
+})
+
+#define DO_ONCE_COND(condition, to_do)		\
+	DO_COND(condition, DO_ONCE(to_do))
+
+#endif /* _LINUX_ONCE_H */
-- 
1.8.3.1

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