linux-kernel - Re: [V2 PATCH] tmpfs: add fallocate support

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Date:	Sat, 19 Nov 2011 15:14:48 +0100
From:	Kay Sievers <kay.sievers@...y.org>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Cong Wang <amwang@...hat.com>, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, Pekka Enberg <penberg@...nel.org>,
	Hugh Dickins <hughd@...gle.com>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	Lennart Poettering <lennart@...ttering.net>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	linux-mm@...ck.org
Subject: Re: [V2 PATCH] tmpfs: add fallocate support

On Sat, Nov 19, 2011 at 11:03, Christoph Hellwig <hch@...radead.org> wrote:
> On Fri, Nov 18, 2011 at 06:39:50PM +0800, Cong Wang wrote:
>> It seems that systemd needs tmpfs to support fallocate,
>> see http://lkml.org/lkml/2011/10/20/275. This patch adds
>> fallocate support to tmpfs.
>
> What for exactly?  Please explain why preallocating on tmpfs would
> make any sense.

To be able to safely use mmap(), regarding SIGBUS, on files on the
/dev/shm filesystem. The glibc fallback loop for -ENOSYS on fallocate
is just ugly.

Kay
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