[dm-devel] Re: [RFC] issues with device mapper snapshots

[Kevin Corry]

On Wednesday 30 June 2004 1:35 pm, Dave Olien wrote:
> I agree with the need for a more generic solution to bio pools.
> Duplicating code in dm-io.c is unfortunate.
>
> I suspect that won't be solvable until 2.7/2.8.
> Probably wouldn't want to make this kind of change in a stable release.
>
> You're right, this is in bio_clone() dm.c, and the local bio allocators are
> statically declared in dm-io.c.
>
> What would you think of creating a bio_set_clone() in dm-io.c, and
> exporting the symbol for use by dm.c, the replace that bio_clone() with
> a call to bio_set_clone().

I believe that should be sufficient for the time being.

I don't think it would be impossible to get this change into fs/bio.c during 
2.6. It would mostly be a matter of setting up the infrastructure (for which 
there would be no initial users). Then we'd want to create a global pool 
(sometime during kernel initialization) that would mimic the existing global 
bio pool. Then make it so calls to bio_clone() and bio_alloc() would always 
go to this global pool, which would mean a minimum of existing kernel code 
would need to change. Then we'd be able to switch users of 
bio_alloc/bio_clone over to private pools as necessary.

-- 
Kevin Corry
kevcorry at us.ibm.com
http://evms.sourceforge.net/