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

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Message-ID: <Pine.LNX.4.64.0709041525080.7326@alien.or.mcafeemobile.com>
Date:	Tue, 4 Sep 2007 15:41:31 -0700 (PDT)
From:	Davide Libenzi <davidel@...ilserver.org>
To:	Michael Kerrisk <mtk-manpages@....net>
cc:	Andrew Morton <akpm@...ux-foundation.org>, corbet@....net,
	jengelh@...putergmbh.de, hch@....de, stable@...nel.org,
	Ulrich Drepper <drepper@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	tglx@...utronix.de, rdunlap@...otime.net
Subject: Re: [PATCH] Revised timerfd() interface

On Tue, 4 Sep 2007, Michael Kerrisk wrote:

> Hi Davide,
> 
> > > <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.
> 
> However, one can have multipe POSIX timers, just as you can 
> have multiple timerfd timers; nevertheless POSIX timers provide
> the get and get-while-setting functionality.

The fact that POSIX defined a certain API in a given way, does not 
automatically mean that every other API has to look exactly like that.
POSIX has the tendency to bloat things up at times ;)



> > and in terms of kernel code footprint.
> 
> Not sure what your concern is here.  The total amount of 
> new code for all of these options is pretty small.

>From your patch:

fs/compat.c              |   34 ++++++++--
fs/timerfd.c             |  147 +++++++++++++++++++++++++++++++++++++++--------
include/linux/compat.h   |    3 
include/linux/syscalls.h |    3 
4 files changed, 153 insertions(+), 34 deletions(-)

And the API definition becomes pretty messy. The other way is to add new 
system calls. 120+ lines of code more of new system calls wouldn't even be 
a problem in itself, if the added value was there.
IMO, as I already said, the added value does not justify them.



- Davide


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