Date: Mon, 30 Nov 2009 17:43:56 +1100
From: Dave Chinner <david@fromorbit.com>
To: Nitin Arora <nitin.arora.del@gmail.com>
Cc: xfs@oss.sgi.com, "sandeen-xfs@sandeen.net" <sandeen-xfs@sandeen.net>,
        "p.mironchik@velesys.com" <p.mironchik@velesys.com>,
        "hch@xfs.org" <hch@xfs.org>
Subject: Re: Writing journal only in Big Endian format
Message-ID: <20091130064356.GD30608@discord.disaster>
References: <409bd82b0911292117n5aa11961u86e787d20acbd2b3@mail.gmail.com>
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On Mon, Nov 30, 2009 at 10:47:41AM +0530, Nitin Arora wrote:
> The problem is that big endian machine cannot recognize the
> journal which was written in little endian format by the little
> endian machine and once the journal is zerod out it can be
> mouted.
> 
> Now the solution to above problem seems writing journal always in
> big endian format.

Or you could just replay the log on the little endian machine and do
a clean unmount, then you should be able to move it to the big
endian machine without losing anything.

> Please suggest me, Is there any design limitation in XFS for this.

No design limitation, just a *lot* of work to change. If you don't
have a few months handy to work on this, I'd just use the above
method....

> Is it okay and feasible to implement it if yes then please give
> some pointers so that it can be implemented,

All log headers, tails and sector fills need to be converted, every log
item format routine needs a big-endian version, log recovery needs
to be able to read both host-format and big-endian logs, all the
userspace tools need to learn about different log formats, QA tests
need to be written, etc.

> under some suitable
> compile time switch.

It could be done with a superblock feature bit, so the same kernel
could support both big-endian logs and host format.

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com