Re: Updated patches for journal checksums.

[Alex Tomas <alex@clusterfs.com>]

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