linux-kernel - Re: [PATCH v3 1/6] fat: add i_disksize to represent uninitialized size

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Message-ID: <87ppn0v3i2.fsf@devron.myhome.or.jp>
Date:	Thu, 06 Feb 2014 21:18:13 +0900
From:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
To:	Namjae Jeon <linkinjeon@...il.com>
Cc:	akpm@...ux-foundation.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Namjae Jeon <namjae.jeon@...sung.com>,
	Amit Sahrawat <a.sahrawat@...sung.com>
Subject: Re: [PATCH v3 1/6] fat: add i_disksize to represent uninitialized size

Namjae Jeon <linkinjeon@...il.com> writes:

>>> fat_fill_inode() just set i_disksize to i_size. So, it is not aligned by
>>> cluster size or block size.
>>>
>>> E.g. ->mmu_private = 500. Then, cont_write_begin() can set ->mmu_private
>>> to 512 on some case. In this case, fat_get_block() will not be called,
>>> because no new allocation.
>>>
>>> If this is true, it would be possible to have ->mmu_private == 512 and
>>> ->i_disksize == 500.
>>>
>>> I'm missing something?
>>
>> BTW, even if above was right, I'm not checking whether updating
>> ->i_disksize after cont_write_begin() is right fix or not.
> I understand your concern. these can be mismatched.  But, when
> checking your doubt, I can not find any side effect.  I think that
> there is no issue regardless of alignment of two value, in the
> cont_write_begin.  Could you please share any point I am missing ?  If
> you suggest checking point or test method, I can check more and share
> the result.

I'm not checking whether it is wrong or not. But, like you said,
->mmu_private > ->i_disksize is wrong in theory.

Although, it might have no real problem.

So, how about to set ->i_disksize to aligned by blocksize at first
(i.e. when initializing the inode)?

This may change the behavior when ->mmu_private is not aligned to
blocksize in current patchset. But, in theory, it is right state
(between ->mmu_private and ->i_disksize is uninitialized). I guess, we
can do it with small adjustments, and keep state valid in theory too.

This is just a my guess, so it might be wrong though. I guess, worth to
try to consider.

Thanks.
-- 
OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
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