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

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Date:	Tue, 19 Feb 2013 00:15:54 +0900
From:	Namjae Jeon <linkinjeon@...il.com>
To:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
Cc:	Andrew Bartlett <abartlet@...ba.org>, 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())

2013/2/18 OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>:
> Namjae Jeon <linkinjeon@...il.com> writes:
>
>>> 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).
>> Hi OGAWA.
>> We don't need to consider device unplugging case ?
>> If yes, I can rework fat fallocate patch as your suggestion.
>
> In my suggestion, I think, kernel crash or something like unplugging
> cases handles has no change from current way.
>
> Any pre-allocated blocks are truncated by fsck as inconsistency state,
> like crash before updating i_size for normal extend write.  I.e. across
> unmount, nobody care whether pre-allocated or not. IOW, if there is
> inconsistent between i_size and cluster chain (includes via
> fallocate(2)) across unmount, it should be handled as broken state.
>
> In short, the lifetime of pre-allocated blocks are from fallocate(2) to
> ->release() only.
Okay, I will post updated fat fallocate patch after looking into more.
Thanks.
>
> Thanks.
> --
> OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
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