linux-kernel - Re: Read support for fat_fallocate()? (was [v2] fat: editions to support fat

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Date:	Tue, 19 Feb 2013 00:11:14 +1100
From:	Andrew Bartlett <abartlet@...ba.org>
To:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
Cc:	Namjae Jeon <linkinjeon@...il.com>, linux-kernel@...r.kernel.org,
	Ravishankar N <cyberax82@...il.com>,
	Amit Sahrawat <amit.sahrawat83@...il.com>,
	Nam-Jae Jeon <namjae.jeon@...sung.com>,
	Ravishankar N <ravi.n1@...sung.com>,
	Amit Sahrawat <a.sahrawat@...sung.com>
Subject: Re: Read support for fat_fallocate()? (was [v2] fat: editions to
 support fat_fallocate())

On Mon, 2013-02-18 at 20:36 +0900, OGAWA Hirofumi wrote:
> Andrew Bartlett <abartlet@...ba.org> writes:

> > Or, if we cannot make any changes to the on-disk format, what about
> > keeping such a database in memory, allocating some of the existing free
> > list to files that have had fallocate() called on them?  (Naturally,
> > this makes it non-persistent, and instead more of a 'hint', but could at
> > least solve our mutual performance issues).
> 
> [...]
> 
> Hm. My concerns are compatibility and reliability. Although We can
> change on-disk format if need, but I don't think it can be compatible
> and reliable. If so, who wants to use it? I feel there is no reason to
> use FAT if there is no compatible.
> 
> Well, anyway, possible solution would be, we can pre-allocate physical
> blocks via fallocate(2) or something, but discard pre-allocated blocks
> at ->release() (or before unmount at least). This way would have
> compatibility (no on-disk change over unmount) and possible breakage
> would be same with normal extend write patterns on kernel crash
> (i.e. Windows or fsck will truncate after i_size).

That would certainly give me what the Samba NAS with USB FAT disk use
case needs.

Thanks,

Andrew Bartlett

-- 
Andrew Bartlett                                http://samba.org/~abartlet/
Authentication Developer, Samba Team           http://samba.org


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