linux-ext4 - Re: [PATCH 3/4]ext4: Return exchanged blocks count to user space in failure

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Message-ID: <87f94c370909030648n84c5814kb04cb6d5e17b3d6e@mail.gmail.com>
Date:	Thu, 3 Sep 2009 09:48:00 -0400
From:	Greg Freemyer <greg.freemyer@...il.com>
To:	Peng Tao <bergwolf@...il.com>
Cc:	Akira Fujita <a-fujita@...jp.nec.com>,
	Theodore Tso <tytso@....edu>, linux-ext4@...r.kernel.org
Subject: Re: [PATCH 3/4]ext4: Return exchanged blocks count to user space in 
	failure

On Thu, Sep 3, 2009 at 1:13 AM, Peng Tao<bergwolf@...il.com> wrote:
> Hi, Greg,
>
> On Thu, Sep 3, 2009 at 4:59 AM, Greg Freemyer<greg.freemyer@...il.com> wrote:
>> Peng,
>>
>> I have not looked at the code very closely, but can you tell me where
>> a file corruption can take place?   Not completing the replacement of
>> extents with donor extents is one thing.  Corrupting the original file
>> contents is another.
> The file corruption is mainly because of the half done replacement.
>
> My test case is here:
> http://marc.info/?l=linux-ext4&m=124992522305319&w=2
>
> With Akira's previous patch
> (http://marc.info/?l=linux-ext4&m=124937430627867&w=2),
> EXT4_IOC_MOVE_EXT does not panic the kernel any more. But it leaves
> the orig file's extent tree corrupted.

Is this highly repeatable, e4defrag using EXT4_IOC_MOVE_EXT corrupts
sparse files?

If so, it seems like a pretty major bug that will be exposed to
userspace when 2.6.31 goes final.

It seems to me at a minimum a Kconfig option should be added to enable
the ioctl to userspace and that it should have depends on EXPERIMENTAL
and default to NO for now.

We don't want people thinking that this feature is stable in 2.6.31.

Greg
-- 
Greg Freemyer
Head of EDD Tape Extraction and Processing team
Litigation Triage Solutions Specialist
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