linux-kernel - Re: [patch 2/4] new timerfd API v2

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Message-ID: <Pine.LNX.4.64.0709251035330.9111@alien.or.mcafeemobile.com>
Date:	Tue, 25 Sep 2007 10:41:47 -0700 (PDT)
From:	Davide Libenzi <davidel@...ilserver.org>
To:	Jonathan Corbet <corbet@....net>
cc:	Michael Kerrisk <mtk-manpages@....net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [patch 2/4] new timerfd API v2 - new timerfd API 

On Tue, 25 Sep 2007, Jonathan Corbet wrote:

> One quick question:
> 
> > Like the previous timerfd API implementation, read(2) and poll(2) are supported
> > (with the same interface).
> 
> Looking at that interface, it appears that a process doing a read() on a
> timerfd with no timer set will block for a very long time.  It's an
> obvious "don't do that" situation, but perhaps we could help an
> occasional developer get a clue by returning something like -EINVAL when
> the timer has not been set?

That is the same as you try to read once more after an expired timer. You 
won't wake up until the next timer event will show up. That is, after at 
most TP time for periodic timers, or after the time  the next 
timerfd_settime() will setup.
I'd like to keep the "timerfd not set yet" and the "timerfd already 
expired and not re-armed" acting the same way. That is, wait till next 
event happen (unless O_NONBLOCK of course).



- Davide


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