linux-kernel - Re: Man page for revised timerfd API

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Message-ID: <47033BA1.7070901@gmx.net>
Date:	Wed, 03 Oct 2007 08:50:09 +0200
From:	Michael Kerrisk <mtk-manpages@....net>
To:	Davide Libenzi <davidel@...ilserver.org>
CC:	rdunlap@...otime.net, Andrew Morton <akpm@...ux-foundation.org>,
	hch@....de, geoff@...are.org.uk, tglx@...utronix.de,
	david@...deman.nu, Ulrich Drepper <drepper@...hat.com>,
	subrata@...ux.vnet.ibm.com, corbet@....net,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Man page for revised timerfd API



Davide Libenzi wrote:
> On Thu, 27 Sep 2007, Michael Kerrisk wrote:
> 
>> Davide,
>>
>> A further question: what is the expected behavior in the
>> following scenario:
>>
>> 1. Create a timerfd and arm it.
>> 2. Wait until M timer expirations have occurred
>> 3. Modify the settings of the timer
>> 4. Wait for N further timer expirations have occurred
>> 5. read() from the timerfd
>>
>> Does the buffer returned by the read() contain the value
>> N or (M+N)?  In other words, should modifying the timer
>> settings reset the expiration count to zero?
> 
> Every timerfd_settime() zeroes the tick counter. So in your scenario it'll 
> return N.

Thanks Davide.

I modified the first para of the read description to make this clear:

       read(2)
              If the timer has already expired one or more times
              since   its  settings  were  last  modified  using
              timerfd_settime(), or since  the  last  successful
              read(2),  then the buffer given to read(2) returns
              an unsigned 8-byte integer  (uint64_t)  containing
              the number of expirations that have occurred.

(In the earlier version of the page the text talked about expirations
"since the timer was created".)

Cheers,

Michael

-- 
Michael Kerrisk
maintainer of Linux man pages Sections 2, 3, 4, 5, and 7

Want to help with man page maintenance?  Grab the latest tarball at
http://www.kernel.org/pub/linux/docs/manpages/
read the HOWTOHELP file and grep the source files for 'FIXME'.

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