Subject: Re: RFC: A revised timerfd API
From: Thomas Gleixner <tglx@linutronix.de>
To: Michael Kerrisk <mtk-manpages@gmx.net>
Cc: Lee.Schermerhorn@hp.com, torvalds@linux-foundation.org,
       vda.linux@googlemail.com, rdunlap@xenotime.net, corbet@lwn.net,
       hch@lst.de, akpm@linux-foundation.org, linux-kernel@vger.kernel.org,
       geoff@gclare.org.uk, drepper@redhat.com, davidel@xmailserver.org,
       David =?ISO-8859-1?Q?H=E4rdeman?= <david@hardeman.nu>
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Date: Tue, 18 Sep 2007 11:42:22 +0200
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On Tue, 2007-09-18 at 11:30 +0200, Michael Kerrisk wrote:
> > This way we have it nicely integrated into the posix timer code and keep
> > the existing semantics of posix timers intact.
> > 
> > We need to think about the open file descriptor in the timer_delete()
> > case as well, but this should be not too hard to sort out.
> 
> This seems like a workable idea also.  But note David Härdeman's
> critique of options c & d: the existence of a coupled timerfd 
> and a timerid means that the application must maintain a mapping
> between the two, so that after an epoll call (for example) that 
> says the timerfd is ready, the timer can be manipulated using
> the corresponding timerfd.  This isn't IMO a fatal flaw, but
> it does make the API a little more clumsy.

Hmm, we might do something like:

	timer_gettime(fd | POSIX_TIMER_FD, .....);

So the kernel looks up the fd in order to figure out the timer_id, which
needs to be referenced in filep->private_data anyway.

	tglx


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