linux-ext4 - Re: Need of revoke mechanism in JBD

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Message-ID: <4DBB6EB9.40100@gmail.com>
Date:	Sat, 30 Apr 2011 07:36:49 +0530
From:	Niraj Kulkarni <kulkarniniraj14@...il.com>
To:	Amir Goldstein <amir73il@...il.com>
CC:	Ted Ts'o <tytso@....edu>, Ding Dinghua <dingdinghua85@...il.com>,
	Yongqiang Yang <xiaoqiangnk@...il.com>,
	linux-ext4@...r.kernel.org
Subject: Re: Need of revoke mechanism in JBD

On Saturday 30 April 2011 01:15 AM, Amir Goldstein wrote:
> On Tue, Apr 26, 2011 at 3:25 PM, Ted Ts'o<tytso@....edu>  wrote:
>> On Tue, Apr 26, 2011 at 05:23:21PM +0800, Ding Dinghua wrote:
>>> I think it's not only a performance issue but more important, a
>>> correctness issue.
>>> Revoke table is used for preventing the wrong replay of journal which
>>> cause data corruption:
>>> If block A has been journalled its modification, committed to journal
>>> and hasn't been checkpointed,
>>> and in later transactions block A is freed and reused for data in
>>> no-journalled-data mode, then If
>>> we don't have revoke table which recording the releasing event, replay
>>> of journal will overwrite the new data,
>>> which causing data corruption.
>> Yes, this is correct.  It should be covered fairly well in Stephen
>> Tweedie's, "Journaling the ext2fs file system" paper, which you can
>> find at:
>>
>> https://ext4.wiki.kernel.org/index.php/Publications
> Actually, the original paper has no mention of revoke records.
> I went out to look for useful documentation on journal forget/revoke
> and came back empty handed as well.
>
>> if you'd like more details.
>>
>> Hope this helps!
>>
>>                                                 - Ted
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Yes, I tried some other papers too, but no use. Anyway I've figured out 
that for my change, I dont need any kind of journalling related 
facilities, so I am going to bypass it completely.

Niraj
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