linux-kernel - Re: [RFC PATCH 2/2] kernel/sched.c: VLA in middle of struct

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Message-ID: <20090513053622.GQ8633@ZenIV.linux.org.uk>
Date:	Wed, 13 May 2009 06:36:22 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	Jeff Garzik <jeff@...zik.org>, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Mike Travis <travis@....com>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>, roland@...hat.com
Subject: Re: [RFC PATCH 2/2] kernel/sched.c: VLA in middle of struct

On Wed, May 13, 2009 at 11:42:26AM +0930, Rusty Russell wrote:
> > > Anyway, since [] is C99, I thought it preferable to [0] which is a gcc
> > > extension.  However, if C99 is really so braindead as to disallow this
> > > fairly standard trick, so I'm happy to go with the gcc extension.[1]
> >
> > No.  There's a standard way to do that in C99; you can put a struct with
> > that thing into a union.
> 
> Ah, thanks for the clue.
> 
> How's this:
> 
> sched: avoid flexible array member inside struct (gcc extension)
> 
> struct sched_group and struct sched_domain end in 'unsigned long
> cpumask[]' which Jeff Garzik notes is not legal to place inside
> another struct.  It upsets sparse and clang (LLVM's C front end).
> 
> Al Viro pointed out that a union is the Right Way to do this.

Acked-by: Al Viro <viro@...iv.linux.org.uk>
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