Re: [Qemu-devel] live migration vs device assignment (motivation)

[Lan, Tianyu]

On 12/10/2015 7:41 PM, Dr. David Alan Gilbert wrote:
> > Ideally, it is able to leave guest driver unmodified but it requires the
> > >hypervisor or qemu to aware the device which means we may need a driver in
> > >hypervisor or qemu to handle the device on behalf of guest driver.
> Can you answer the question of when do you use your code -
>     at the start of migration or
>     just before the end?

Just before stopping VCPU in this version and inject VF mailbox irq to
notify the driver if the irq handler is installed.
Qemu side also will check this via the faked PCI migration capability
and driver will set the status during device open() or resume() callback.

> > > > >It would be great if we could avoid changing the guest; but at least your 
> > > guest
> > > > >driver changes don't actually seem to be that hardware specific; could your
> > > > >changes actually be moved to generic PCI level so they could be made
> > > > >to work for lots of drivers?
> > >
> > >It is impossible to use one common solution for all devices unless the PCIE
> > >spec documents it clearly and i think one day it will be there. But before
> > >that, we need some workarounds on guest driver to make it work even it looks
> > >ugly.

Yes, so far there is not hardware migration support and it's hard to 
modify bus level code. It also will block implementation on the Windows.

> Dave