linux-kernel - Re: [PATCH] fs/direct-io.c: Calcuate fs_count correctly in get_more

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Date:	Mon, 19 Sep 2011 15:31:49 -0700
From:	Andrew Morton <akpm@...gle.com>
To:	Tao Ma <tm@....ma>
Cc:	linux-kernel@...r.kernel.org, "Theodore Ts'o" <tytso@....edu>,
	Christoph Hellwig <hch@....de>,
	Al Viro <viro@...iv.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] fs/direct-io.c: Calcuate fs_count correctly in
 get_more_blocks.

On Mon, 19 Sep 2011 16:25:39 +0800
Tao Ma <tm@....ma> wrote:

> In get_more_blocks, we use dio_count to calcuate fs_count and do some
> tricky things to increase fs_count if dio_count isn't aligned. But
> actually it still has some cornor case that can't be coverd. See the
> following example:
> ./dio_write foo -s 1024 -w 4096(direct write 4096 bytes at offset 1024).
> The same goes if the offset isn't aligned to fs_blocksize.
> 
> In this case, the old calculation counts fs_count to be 1, but actually
> we will write into 2 different blocks(if fs_blocksize=4096). The old code
> just works, since it will call get_block twice(and may have to allocate
> and create extent twice for file systems like ext4). So we'd better call
> get_block just once with the proper fs_count.

Has this been carefully tested with more than just ext4?  If so, which?

Thanks.
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