linux-kernel - Re: [PATCH] Introduce down_try() so we can move away from down

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Message-Id: <200807292301.18733.rusty@rustcorp.com.au>
Date:	Tue, 29 Jul 2008 23:01:17 +1000
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	"Paul Menage" <menage@...gle.com>
Cc:	"Linus Torvalds" <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, "Matthew Wilcox" <matthew@....cx>,
	"Randy.Dunlap" <rdunlap@...otime.net>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Christoph Hellwig" <hch@...radead.org>
Subject: Re: [PATCH] Introduce down_try() so we can move away from down_trylock()

On Tuesday 29 July 2008 10:27:15 Paul Menage wrote:
> On Mon, Jul 28, 2008 at 5:15 PM, Rusty Russell <rusty@...tcorp.com.au> wrote:
> > +/**
> > + * down_try - try to down a semaphore, but don't block
> > + * @sem: the semaphore
>
> Is there a reason to avoid using a return type of "bool" for this?

Probably, but not a good one.

This incorporates Andrew's whitespace fix as well (ie:
introduce-down_try-so-we-can-move-away-from-down_trylock.patch and
introduce-down_try-so-we-can-move-away-from-down_trylock-checkpatch-fixes.patch)

Introduce down_try()

I planned on removing the much-disliked down_trylock() (with its
backwards return codes) in 2.6.27, but it's creating something of a
logjam with other patches in -mm and linux-next.

Andrew suggested introducing "down_try" as a wrapper now, to make
the transition easier.

Signed-off-by: Rusty Russell <rusty@...tcorp.com.au>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Christoph Hellwig <hch@...radead.org>
Cc: Matthew Wilcox <matthew@....cx>
Cc: Stephen Rothwell <sfr@...b.auug.org.au>
---
 include/linux/semaphore.h |   14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff -r 92664ae4130b include/linux/semaphore.h
--- a/include/linux/semaphore.h	Wed May 21 14:54:40 2008 +1000
+++ b/include/linux/semaphore.h	Wed May 21 15:07:31 2008 +1000
@@ -48,4 +48,18 @@ extern int __must_check down_timeout(str
 extern int __must_check down_timeout(struct semaphore *sem, long jiffies);
 extern void up(struct semaphore *sem);
 
+/**
+ * down_try - try to down a semaphore, but don't block
+ * @sem: the semaphore
+ *
+ * This is equivalent to down_trylock(), but has the same return codes as
+ * spin_trylock and mutex_trylock: 1 if semaphore acquired, 0 if not.
+ *
+ * down_trylock() with its confusing return codes will be deprecated
+ * soon.  It will not be missed.
+ */
+static inline bool __must_check down_try(struct semaphore *sem)
+{
+	return !down_trylock(sem);
+}
 #endif /* __LINUX_SEMAPHORE_H */

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