[dm-devel] Re: dm snapshot: allow live exception store handover between tables

[Mike Snitzer <snitzer redhat com>]

On Fri, Nov 06 2009 at  2:41pm -0500,
Alasdair G Kergon <agk redhat com> wrote:

> On Fri, Nov 06, 2009 at 02:26:21PM -0500, Mike Snitzer wrote:
> > OK, actually in practice 'lvchange --refresh' is:
> > old->suspend
> > new->ctr
> 
> Those two need to be swapped.
> (I think it's a pre-existing userspace bug that's simple to fix.)

Why do they _need_ to be swapped?

> > old->resume
> >  - device-mapper: snapshots: Unable to handover exceptions to another snapshot on resume.
> > new->resume
> >  - snapshot_resume: handing over exceptions
> 
> Handover to new device and make it live first, then remove old device.
> It doesn't make sense to me to remove the old device before the new one has
> successfully taken over from it.

OK, I'm not sure how to make that happen within lvm2's deptree.  I'll
have a look.  So you're saying refresh should result in:

new->ctr
old->suspend
new->resume
old->resume

Mike