Re: [RFC V7 2/3] libxl domain snapshot API design

[Ian Campbell <Ian.Campbell@citrix.com>]

On Tue, 2014-10-21 at 21:59 -0600, Chun Yan Liu wrote:
> > Is this operation any different to destroying the domain and using 
> > libxl_domain_restore to start a new domain based on the snapshot? Is 
> > this operation just a convenience layer over that operation? 
> 
> It depends on implementation. It's a simple way to destroy the domain
> first, then start new domain based on snapshot. But destroying the
> domain may be not good to user (after xl snapshot-revert, domid is
> changed.)  and may cause some problem in libvirt (may affect its
> event handling ?).

I would hope that as part of the implementation libvirt would learn to
cope with this if it can't already, but it can surely already cope with
migration and reverting to a snapshot is not so very different.

> Or another way is: not destroying the domain, but through a process
> like pause domain, reload memory, reload disk snapshot, reload config
> file, resume domain. Complex but maybe better.

I don't think the complexity of resetting an already existing domain's
memory and i/o state to an earlier incarnation rather than starting from
a clean slate should be underestimated either (TBH it never occurred to
me that you might try this). AFAICT you'd need to effectively tear
everything down to a blank slate and then do all the same things that
you would do in the destroy case.

Ian.