linux-kernel - Re: [PATCH] Revised timerfd() interface

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Message-Id: <200709051312.21873.vda.linux@googlemail.com>
Date:	Wed, 5 Sep 2007 13:12:21 +0100
From:	Denys Vlasenko <vda.linux@...glemail.com>
To:	Davide Libenzi <davidel@...ilserver.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Michael Kerrisk <mtk-manpages@....net>, rdunlap@...otime.net,
	tglx@...utronix.de,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ulrich Drepper <drepper@...hat.com>, stable@...nel.org,
	hch@....de, jengelh@...putergmbh.de, corbet@....net
Subject: Re: [PATCH] Revised timerfd() interface

On Tuesday 04 September 2007 16:25, Davide Libenzi wrote:
> On Tue, 4 Sep 2007, Andrew Morton wrote:
> 
> > > On Tue, 04 Sep 2007 10:03:56 +0200 Michael Kerrisk <mtk-manpages@....net> wrote:
> > > Davide,
> > > 
> > > >> Davide -- ping!  Can you please offer your comments about this change, and
> > > >> also thoughts on Jon's and my comments about a more radical API change
> > > >> later  in this thread.
> > > > 
> > > > IMO the complexity of the resulting API (and resulting patch), and the ABI 
> > > > change, is not justified by the added value.
> > > 
> > > Neither of the proposed APIs (either my multiplexed version of timerfd()
> > > or Jon's/my idea of using three system calls (like POSIX timers), or
> > > the notion of timerfd() integrated with POSIX timers) is more
> > > complicated than the existing POSIX timers API.
> > > 
> > > The ABI change doesn't really matter, since timerfd() was broken in 2.6.22
> > > anyway.
> > > 
> > > Both previous APIs provided the features I have described provide:
> > > 
> > > * the ability to fetch the old timer value when applying
> > >   a new setting
> > > 
> > > * the ability to non-destructively fetch the amount of time remaining
> > >   on a timer.
> > > 
> > > This is clearly useful for timers -- but you have not explained why
> > > you think this is not necessary for timerfd timers.
> > 
> > <wakes up>
> > 
> > I'd have thought that the existing stuff would be near-useless without the
> > capabilities which you describe?
> 
> Useless like it'd be a motorcycle w/out a cup-holder :)
> Seriously, the ability to get the previous values from "something" could 
> have a meaning if this something is a shared global resource (like signals 
> for example). In the timerfd case this makes little sense, since you can 
> create as many timerfd as you like and you do not need to share a single 
> one by changing/restoring the original context.

I think at least ability to read remaining time from a timerfd is needed.
--
vda
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