[Tux3] Design note: Log, commit, rebuild

[Daniel Phillips]

On Sunday 04 January 2009 05:47, Manish Katiyar wrote:
> On Sun, Jan 4, 2009 at 3:20 PM, Daniel Phillips <phillips at phunq.net> wrote:
> > ...to be continued.  That note didn't say much about commit and rebuild.
> 
> Hi Daniel,
> 
> I am still a novice in file systems and reading about tux3 excites me
> about the interesting problems and the way you are fixing it. However
> I could not actually understand how are you dealing with the "allocate
> in allocate" problem in the above mail. Could you please give more
> details on it too in your next mail when you tell about commit and
> rebuild (if it doesn't waste much of your time)

The fork operation essentially provides a way to snapshot bitmap
cache.  The allocate-in-allocates still happen during bitmap flushing,
but they do not change the bitmap images that will be written out,
because any changed blocks will be forked.  Any new allocations that
take place during bitmap flushing will be logged instead of appearing
in the bitmaps being written out, which is just what we want.

There are more details of just how to implement this to be sure, but
perhaps some code would be a useful way to clarify the details.

Regards,

Daniel


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