To: Ingo Molnar <mingo@elte.hu>
Cc: linux <linux-kernel@vger.kernel.org>
Subject: Re: [patch, 2.6.11-rc2] sched: RLIMIT_RT_CPU_RATIO feature
References: <20050125135613.GA18650@elte.hu> <87sm4opxto.fsf@sulphur.joq.us>
	<20050126070404.GA27280@elte.hu> <87fz0neshg.fsf@sulphur.joq.us>
	<1106782165.5158.15.camel@npiggin-nld.site>
	<874qh3bo1u.fsf@sulphur.joq.us>
	<1106796360.5158.39.camel@npiggin-nld.site>
	<87pszr1mi1.fsf@sulphur.joq.us> <20050127113530.GA30422@elte.hu>
	<873bwfo8br.fsf@sulphur.joq.us> <20050202113705.GA25012@elte.hu>
From: "Jack O'Quin" <joq@io.com>
Date: Wed, 02 Feb 2005 10:01:20 -0600
In-Reply-To: <20050202113705.GA25012@elte.hu> (Ingo Molnar's message of
 "Wed, 2 Feb 2005 12:37:05 +0100")
Message-ID: <874qgvj6i7.fsf@sulphur.joq.us>
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[trimming the Cc: list]

> * Jack O'Quin <joq@io.com> wrote:
>> Remember when I asked how you handle changes to sizeof(struct rusage)?
>> That was a serious question.  I hope there's a solution. [...]

Ingo Molnar <mingo@elte.hu> writes:
> what does any of what we've talking about have to do with struct rusage? 

Your previous message implied that "userspace" programmers don't
understand binary compatibility...

> you might ask yourself, 'why is this so, and why cannot the Linux guys
> apply pretty much any hack as e.g. userspace code might'

I was just demonstating that I do.

> " > Does getrusage() return anything for this?  How can a field be added
>   > to the rusage struct without breaking binary compatibility?  Can we
>   > assume that no programs ever use sizeof(struct rusage)?
>
>   rlimits are easily extended and there are no binary compatibility
>   worries. The kernel doesnt export the maximum towards userspace.
>   getrusage() will return the value on new kernels and will return 
>   -EINVAL on old kernels, so new userspace can deal with this 
>   accordingly. "
>
> (and here i meant getrlimit(), not getrusage() - getrusage() is not
> affected by the patch at all.)

Well, that was source of my question.

I had asked about rusage.  You said it did return a new value, but
that this was not a problem.  That made no sense to me.  Thank you for
clearing it up.

Certainly getrlimit() works OK.  I understood that already.
-- 
  joq
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