linux-ext4 - Re: Updated patches for journal checksums.

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Message-ID: <46779D9D.2090109@clusterfs.com>
Date:	Tue, 19 Jun 2007 13:10:53 +0400
From:	Alex Tomas <alex@...sterfs.com>
To:	Andreas Dilger <adilger@...sterfs.com>
CC:	Girish Shilamkar <girish@...sterfs.com>,
	Ext4 Mailing List <linux-ext4@...r.kernel.org>,
	Theodore Tso <tytso@....edu>
Subject: Re: Updated patches for journal checksums.

Andreas Dilger wrote:
> I _think_ Alex is asking "what happens if during a transaction undergoing
> checkpoint of blocks to filesystem (not the last one in the journal) is
> interrupted by a crash and upon restart the partially-checkpointed
> transaction is found to have a checksum error?"

yup, thanks for clarification.

>>> what do we do if transaction in the journal is found with wrong
>>> checksum? leave partial transaction in-place?
>> The sanity of the transaction is checked in PASS_SCAN. And if checksum
>> is found to be incorrect for nth transaction then last transaction which
>> is written to disk is (n - 1).
> 
> The recovery.c code (AFAIK) does not do replay for any transaction that
> does not have a valid checksum, or transactions beyond that.  If the
> bad transaction had already started chekpoint (i.e. isn't the last
> committed transaction) then the journal _should_ return an error up to
> the filesystem, so it can call ext4_error() at startup.  For e2fsck
> (which normally does journal replay & recovery) it can do a full
> filesystem check at this point.

hmm. it actually can be last transaction (following no activity?)

thanks, Alex


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