Re: [Qemu-devel] [PATCH] spapr: fix memory hotplug error path

[Bharata B Rao <bharata@linux.vnet.ibm.com>]

On Tue, Jul 04, 2017 at 10:02:46AM +0200, Greg Kurz wrote:
> > > There is some history to this. I was doing error recovery and propagation
> > > here similarly during memory hotplug development phase until Igor
> > > suggested that we shoudn't try to recover after we have done guest
> > > visible changes.
> > > 
> > > Refer to "changes in v6" section in this post:
> > > https://lists.gnu.org/archive/html/qemu-ppc/2015-06/msg00296.html
> > > 
> > > However at that time we were doing memory add by DRC index method
> > > and hence would attach and online one LMB at a time.
> > > In that method, if an intermediate attach fails we would end up with a few
> > > LMBs being onlined by the guest already. However subsequently
> > > we have switched (optionally, based on dedicated_hp_event_source) to
> > > count-indexed method of hotplug where we do attach of all LMBs one by one
> > > and then request the guest to hotplug all of them at once using count-indexed
> > > method.
> > > 
> > > So it will be a bit tricky to abort for index based case and recover
> > > correctly for count-indexed case.  
> > 
> > Looked at the code again and realized that though we started with
> > index based LMB addition, we later switched to count based addition. Then
> > we added support for count-indexed type subject to the presence
> > of dedidated hotplug event source while still retaining the support
> > for count based addition.
> > 
> > So presently we do attach of all LMBs one by one and then do onlining
> > (count based or count-indexed based) once. Hence error recovery
> > for both cases would be similar now. So I guess you should take care of
> > undoing pc_dimm_memory_plug() like Igor mentioned and also undo the
> > effects of partial successful attaches.
> > 
> 
> I've sent a v2 that adds rollback.

oh ok, somehow v2 didn't reach me at all and I saw the v2 in archives only
now. So just noting that my above replies were sent w/o being aware of v2 :)

> > > 
> > > Regards,
> > > Bharata.