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

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Date:	Fri, 7 Feb 2014 13:23:47 +0900
From:	Namjae Jeon <linkinjeon@...il.com>
To:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
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

2014-02-06, OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>:
> 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)?
Yes, It is good idea.
>
> 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.
Right.
>
> This is just a my guess, so it might be wrong though. I guess, worth to
> try to consider.
Okay, I will include it in next patch-set after checking.

Thanks for your review!
>
> Thanks.
> --
> OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
>
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