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Re: [libvirt] [Xen-devel] [PATCH] libxl: support domainReset



On Tue, 2014-08-05 at 20:30 +0100, Wei Liu wrote:
> On Tue, Aug 05, 2014 at 07:45:48PM +0100, Ian Campbell wrote:
> [...]
> > > > > Sure.  I think having an API that emulates a power reset button would be
> > > > > a nice addition to libxl's domain operations.  The destroy/start
> > > > > approach incurs a small bit of overhead, which would be avoided with
> > > > > such an API.  Clients (perhaps incorrectly) implementing their own
> > > > > notion of reset  would also be avoided.
> > > > 
> > > > I think this ought to become pretty easy once Wei's patches to record
> > > > the guest cfg in libxl are completed. Wei -- what do you think?
> > > > 
> > > 
> > > I don't think this "reset" API will need to record any state, i.e. this
> > > feature looks unrelated to my work. What do I miss?
> > 
> > It's a forced reboot, so the API would need to destroy and then recreate
> > the domain. Recreate would need to use the state your patches arrange
> > for libxl to store.
> > 
> 
> Oh you were talking about pesisting state across hard reset, that's of
> course achievable. I think hard reset is more or less the same as
> reboot.
> 
> That's still somewhat orthogonal to my work though. Not having the
> capability to presist state across in libxl doesn't prevent us from
> introducing "reset". I think this is the status quo of "reboot" API,
> isn't it?

There is no "reboot" API in the sense we are talking about.
libxl_domain_reboot() asks the guest to reboot itself. The resulting
actual reboot is handled by the toolstack receiving
LIBXL_EVENT_TYPE_DOMAIN_DEATH and using libxl_domain_destroy
+libxl_domain_create to recreate the domain, prior to your changes only
the toolstack app could do this because only xl/libvirt knew the actual
domain cfg. With your changes a new libxl_domain_hard_reboot could, I
think, be written which does the reboot.

Ian.


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