linux-kernel - Re: [PATCH] fs: add FD_CLOFORK and O

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Date:	Sat, 07 May 2011 14:32:05 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:	Changli Gao <xiaosuo@...il.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Matthew Wilcox <matthew@....cx>, Arnd Bergmann <arnd@...db.de>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arch@...r.kernel.org
Subject: Re: [PATCH] fs: add FD_CLOFORK and O_CLOFORK

Le samedi 07 mai 2011 à 13:41 +0200, Geert Uytterhoeven a écrit :
> On Sat, May 7, 2011 at 08:29, Eric Dumazet <eric.dumazet@...il.com> wrote:
> > I am sure the following idea already was discussed in the past :
> >
> > Embed the close_on_exec / close_on_close bits in the low order bits of
> > file pointers.
> 
> How many low order bits do you expect to have in file pointers?
> Are files allocated using kmalloc(), or do they just obey the alignment of the
> individual members of a file struct? In the latter case, you'll have onlyv1 low
> order bit to play with on m68k.

We should have two bits at a very minimum.

clone_on_exec & clone_on_fork would fit.

filp are allocated with a kmem_cachep with cache line alignement.

filp_cachep = kmem_cache_create("filp", sizeof(struct file), 0,
	SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL);

So in practice we should have more than two bits ;)



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