linux-kernel - Re: Problems with timerfd()

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Date:	Tue, 24 Jul 2007 17:56:18 +0200
From:	"Michael Kerrisk" <mtk-manpages@....net>
To:	"Ray Lee" <ray-lk@...rabbit.org>
Cc:	akpm@...l.org, linux-kernel@...r.kernel.org, torvalds@...l.org,
	davidel@...ilserver.org, drepper@...hat.com
Subject: Re: Problems with timerfd()

> > > (This is the same sort of thing we already have to deal with in
> > > certain situations, such as network stat counters on 32 bit
> > > platforms.)
> >
> > But userspace can't deal with the condition accurately,
> 
> Okay, perhaps this is where I'm missing something? If userspace wakes
> up once every hour, checks the overrun counter against the previous
> (new-old), and goes back to sleep, that'd be good enough, right?

Yes.

> > so why
> > require userspace to worry about this when we could just use
> > a 64-bit value instead?
> 
> <shrug> I don't have strong feelings either way. It just seemed like
> something that could already be taken care of with today's interface.
> Given that the discussion was about an API change between 2.6.22 and
> 2.6.23, I was looking for options to avoid that.

In fact I don't have strong feelings on this part of the interface
design either.  I pointed out the limitation to Davide, and 
pointed out that the related eventfd interface read()s an 8-byte 
integer, and Davide then just fired off a patch to Andrew which 
went into --mm.

It's the other problems with the interface that bother me more
(inability to retrieve previous setting when changing
the timer; inability to retrieve time until next expiration
without changing the current setting).

Cheers,

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

Want to help with man page maintenance?  
Grab the latest tarball at
http://www.kernel.org/pub/linux/docs/manpages , 
read the HOWTOHELP file and grep the source 
files for 'FIXME'.

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