linux-kernel - [PATCH] docbook: some kernel-locking fixes

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Date:	Wed, 2 Apr 2008 14:47:50 -0700
From:	Randy Dunlap <rdunlap@...otime.net>
To:	lkml <linux-kernel@...r.kernel.org>
Cc:	rusty@...tcorp.com.au, akpm <akpm@...ux-foundation.org>,
	mattilinnanvuori@...oo.com
Subject: [PATCH] docbook: some kernel-locking fixes

From: Matti Linnanvuori <mattilinnanvuori@...oo.com>

Fix a wrong path. Add a chapter about try functions.

http://bugzilla.kernel.org/show_bug.cgi?id=9011

Signed-off-by: Matti Linnanvuori <mattilinnanvuori@...oo.com>
Signed-off-by: Randy Dunlap <randy.dunlap@...cle.com>

---
 Documentation/DocBook/kernel-locking.tmpl |   25 +++++++++++++++++++-
 1 file changed, 24 insertions(+), 1 deletion(-)

--- lin2625-rc8-kdoc.orig/Documentation/DocBook/kernel-locking.tmpl
+++ lin2625-rc8-kdoc/Documentation/DocBook/kernel-locking.tmpl
@@ -290,7 +290,7 @@
      <para>
        If you have a data structure which is only ever accessed from
        user context, then you can use a simple semaphore
-       (<filename>linux/asm/semaphore.h</filename>) to protect it.  This 
+       (<filename>include/asm/semaphore.h</filename>) to protect it.  This
        is the most trivial case: you initialize the semaphore to the number 
        of resources available (usually 1), and call
        <function>down_interruptible()</function> to grab the semaphore, and 
@@ -703,6 +703,29 @@
 </sect1>
 </chapter>
 
+<chapter id="try-variants">
+ <title>The try variants</title>
+
+  <para>
+    <function>spin_trylock()</function> does not spin but returns non-zero if
+    it acquires the spinlock on the first try or 0 if not.
+  </para>
+
+  <para>
+    <function>mutex_trylock()</function> does not suspend your task
+    but returns non-zero if it could lock the mutex on the first try
+    or 0 if not.
+  </para>
+
+  <para>
+    <function>down_trylock()</function> does not suspend your task
+    but returns 0 if it could get the semaphore on the first try or
+    non-zero if not. The return value is the inverse of that of
+    <function>spin_trylock()</function> and <function>mutex_trylock()
+    </function>.
+  </para>
+</chapter>
+
   <chapter id="Examples">
    <title>Common Examples</title>
     <para>


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