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

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Date:	Tue, 04 Sep 2007 22:49:32 +0200
From:	"Michael Kerrisk" <mtk-manpages@....net>
To:	Davide Libenzi <davidel@...ilserver.org>, akpm@...ux-foundation.org
Cc:	corbet@....net, jengelh@...putergmbh.de, hch@....de,
	stable@...nel.org, drepper@...hat.com,
	torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org,
	tglx@...utronix.de, rdunlap@...otime.net
Subject: Re: [PATCH] Revised timerfd() interface

> > > 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.

Davide,

As I think about this more, I see more problems with
your argument.  timerfd needs the ability to get and 
get-while-setting just as much as the earlier APIs.
Consider a library that creates a timerfd file descriptor that
is handed off to an application: that library may want
to modify the timer settings without having to create a
new file descriptor (the app mey not be able to be told about
the new fd).  Your argument just doesn't hold, AFAICS.

Cheers,

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

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