Re: Algorithm for nodatacow is broken

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On Wed, 2008-07-16 at 15:41 +0800, Yan Zheng wrote:
> Hello,
> 
> Yesterday, I realized the algorithm for nodatacow is broken, it can't
> reliably detect whether a given extent is referenced by only one
> snapshot.

I had to change around nodatacow back in May because it was definitely
broken in the way you describe.  I agree the special case I added to
allow nodatacow when one of the references comes from the running
transaction is broken.

But, we should be able to fix it by extending the reference count checks
up the tree.  Any reference > 1 not held by the running transaction on
any block should force a cow.

-chris


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