linux-kernel - Re: 2.6.19-rc2-mm2 : empty files on vfat file system

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Date:	Sun, 22 Oct 2006 18:11:36 +0900
From:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
To:	Nick Piggin <npiggin@...e.de>
Cc:	Andrew Morton <akpm@...l.org>, Damien Wyart <damien.wyart@...e.fr>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: 2.6.19-rc2-mm2 : empty files on vfat file system

Nick Piggin <npiggin@...e.de> writes:

> On Sun, Oct 22, 2006 at 05:38:38AM +0900, OGAWA Hirofumi wrote:
>> 
>> As I said in this thread, generic_cont_expand() uses "to == from".
>> Should we fix generic_cont_expand() instead? I don't know the
>> background of this patch.
>
> OK I have to write an RFC for various fs developers, so I'll be sure
> to include you.
>
> We want to be able to pass in a short (possibly zero) commit_write
> length if the page data can not be fully copied.

Thanks. So, if the range is zero, what should fs driver do?

> generic_cont_expand seems to be using that as a shorthand for
> "update the i_size but don't mark anything uptdoate"? If so, I think
> it would be nice to fix it. Why does it even need to go through the
> prepare/commit?

It's not only for updating ->i_size.

__generic_cont_expand() is used for expanding ->i_size by trucate(2).
In FAT case, it needs to fill the hole by zero and dirty it before
write new ->i_size. The ->prepare_write() does it, and ->commit_write()
writes ->i_size and dirty inode in __generic_cont_expand().

Anyway, if it's required, maybe we would be able to change
__generic_cont_expand().
-- 
OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
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