On Wed, Oct 07 2009 at 2:24pm -0400,
Mike Snitzer <snitzer@xxxxxxxxxx> wrote:
> On Wed, Oct 07 2009 at 1:38pm -0400,
> Jonathan Brassow <jbrassow@xxxxxxxxxx> wrote:
>
> > If this is really something that we have to do, then fine. However, it
> > appears that you are doing this to pull out 'ti' and 'cow'... things that
> > are separate by structure from the underlying exception store... which is
> > ultimately what you want to hand over. It seems to me that there is
> > probably a better/cleaner way to do this, while simultaneously leaving
> > 'ti' and 'cow' in their current place.
>
> Yes, both 'ti' and 'cow' are seperate structures within the exception store.
> Yes, we want to handover the exception store itself (but keeping 'ti' and
> 'cow' fixed).
>
> So you're saying have the handover be:
> 1) swap the 'complete' exception_table
> 2) swap the 'cow' and 'ti' in the 2 exception stores
> 3) swap the exception stores
>
> Something like the following?:
>
> static void handover_exceptions(struct dm_snapshot *old,
> struct dm_snapshot *new)
> {
> union {
> struct exception_table table_swap;
> struct dm_target *ti_swap;
> struct dm_dev *cow_swap;
> struct dm_exception_store *store_swap;
> } u;
>
> u.table_swap = new->complete;
> new->complete = old->complete;
> old->complete = u.table_swap;
>
> u.ti_swap = new->store->ti;
> new->store->ti = old->store->ti;
> old->store->ti = u.ti_swap;
>
> u.cow_swap = new->store->cow;
> new->store->cow = old->store->cow;
> old->store->cow = u.cow_swap;
>
> u.store_swap = new->store;
> new->store = old->store;
> old->store = u.store_swap;
>
> old->active = 0;
> new->handover = 0;
> }
Jon,
I discussed this with Mikulas and he agreed that the above would work.
But he raised the fact that reverting dm-snapshot-refactor-associations
leaves the dm_snapshot and dm_exception_store structures muddled with
regard to where per-target members are located. I'm inclined to agree
with him.
The dm-snapshot-refactor-associations patch offers cleanup so that:
1) dm_exception_store only contains exception store-specific members
2) dm_snapshot is the structure that contains per-target members
So while this dm-snapshot-refactor-associations patch could be viewed as
"avoidable churn" it actually takes the data structures in a more
controlled direction.
I would rather dm-snapshot-refactor-associations be applied.
Mike
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