Re: Read support for fat_fallocate()? (was [v2] fat: editions tosupport fat_fallocate())

From: Namjae Jeon
Date: Mon Feb 18 2013 - 10:16:02 EST

2013/2/18 OGAWA Hirofumi <hirofumi@xxxxxxxxxxxxxxxxxx>:
> Namjae Jeon <linkinjeon@xxxxxxxxx> 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.
> --
> OGAWA Hirofumi <hirofumi@xxxxxxxxxxxxxxxxxx>
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