Btrfs devel - Jul 2008 - [PATCH] New nodatacow checker

Hello,

This is updated version of nodatacow patch. To check whether a given
file extent is referenced by multiple snapshots, the checker walks
down the fs tree through dead root and checks all tree blocks in the
path. We can easily detect whether a given tree block is directly
referenced by other snapshot. We can also detect any indirect
reference from other snapshot by checking reference''s generation. The
checker can always detect multiple references, but can''t reliably
detect cases of single reference. So btrfs may do file data cow even
there is only one reference.

Regards
YZ

On Wed, 2008-07-30 at 01:40 +0800, Yan Zheng wrote:
> Hello,
> 
> This is updated version of nodatacow patch. To check whether a given
> file extent is referenced by multiple snapshots, the checker walks
> down the fs tree through dead root and checks all tree blocks in the
> path. We can easily detect whether a given tree block is directly
> referenced by other snapshot. We can also detect any indirect
> reference from other snapshot by checking reference''s generation.
The
> checker can always detect multiple references, but can''t reliably
> detect cases of single reference. So btrfs may do file data cow even
> there is only one reference.
> 
Wonderful, thanks!  I''ll put this in tonight or tomorrow morning.

-chris


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