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Date:	Mon, 11 Apr 2011 09:50:06 +0800
From:	Yongqiang Yang <xiaoqiangnk@...il.com>
To:	"Ted Ts'o" <tytso@....edu>
Cc:	bugzilla-daemon@...zilla.kernel.org, damien@...ssart.com,
	feng.tang@...el.com, linux-ext4@...r.kernel.org
Subject: Re: [Bug 32972] New: EXT4 causes corrupt BitTorrent downloads

On Mon, Apr 11, 2011 at 9:46 AM, Ted Ts'o <tytso@....edu> wrote:
> On Sun, Apr 10, 2011 at 10:30:13PM +0800, Yongqiang Yang wrote:
>> So the right code should be:
>>
>>       bh->b_state = (bh->b_state & ~EXT4_MAP_FLAGS) | map.m_flags;
>>       map_bh(bh, inode->i_sb, map.m_pblk);
>>       if (buffer_unwritten(bh)) {
>>               /* A delayed write to unwritten bh should be marked
>>                * new and mapped.  Mapped ensures that we don't do
>>                * get_block multiple times when we write to the same
>>                * offset and new ensures that we do proper zero out
>>                * for partial write.
>>                */
>>               set_buffer_new(bh);
>>       }
>
> Actually, I'm much more comfortable backing out commit 6de9843da
> entirely.  The above is *not* equivalent to what we had before ---
> consider the case where ext4_map_blocks returns !EXT4_MAP_MAPPED &&
> !EXT4_MAP_UNWRITTEN.
>
> I don't *think* this should happen in the case where ext4_map_blocks
> returns a value > 0, but the fact that it's not obvious, means I'd
> much rather keep things the way that they are.  It's not like dropping
> the set_buffer_mapped(bh) was saving anything measurable anyway....
Agree.  this way, the comment for unwritten case is also much clearer.

Yongqiang
>
>                                                - Ted
>



-- 
Best Wishes
Yongqiang Yang
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