Re: [Qemu-devel] [PATCH 2/2] migration: send and check the devices between source and distination at the begining

[Dr. David Alan Gilbert]

* Li Zhijian (address@hidden) wrote:
> 
> 
> On 09/30/2016 02:15 PM, Amit Shah wrote:
> > Hi,
> > 
> > On (Thu) 29 Sep 2016 [19:06:32], Li Zhijian wrote:
> > > Priviously, if the source and distination have different devices, source 
> > > could goto
> > > the status "paused (postmigrate)", and the distination will exit that 
> > > means no qemu
> > > is alive.
> > > 
> > > After this patch, at above case, source can dectect the some error early 
> > > from distination
> > > and stop the migration, source keep in status "running".
> > 
> > How would incoming migrations from previous versions work?
> 
> You are right. we need to consider more.
> 
> How about that:
> we need to introduce a new section type(e.g: QEMU_VM_SECTION_DEVICE_LIST).
> 
> source side:
> - at the beginning of qemu_savevm_state_begin(), send 
> QEMU_VM_SECTION_DEVICE_LIST first
> - original path
> 
> dst side:
> - if we got the QEMU_VM_SECTION_DEVICE_LIST, have a check with the 
> devices(name,version)
> - otherwise original path

Yes, and only send it on new machine types.
I think a list could be a good idea; I don't worry too much about the 'paused 
(postmigrate)'
case, because libvirt can spot that the destination failed and then restart the 
source,
however a list would also fix the opposite case; where the destination has an 
extra device
that the source does not have, in most cases I think that doesn't cause a 
failure at the moment
but the device has an unusual state.

A QEMU_VM_SECTION_DEVICE_LIST would work, but perhaps a subsection of 
vmstate_globalstate
would work?

Dave

> 
> Please correct me.
> 
> Thanks
> Zhijian
> 
> > 
> > 
> >             Amit
> > 
> > 
> > 
> 
> 
> 
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK