On 6/3/19 4:24 AM, Jens Freimann wrote:
On Fri, May 31, 2019 at 06:47:48PM -0300, Eduardo Habkost wrote:
On Thu, May 30, 2019 at 04:56:45PM +0200, Jens Freimann wrote:
On Tue, May 28, 2019 at 11:04:15AM -0400, Michael S. Tsirkin wrote:
> On Tue, May 21, 2019 at 10:45:05AM +0100, Dr. David Alan Gilbert
wrote:
> > * Jens Freimann (jfreim...@redhat.com) wrote:
[...]
> > > + }
> > > + if (migration_in_setup(s) && !should_be_hidden &&
n->primary_dev) {
> > > + qdev_unplug(n->primary_dev, &err);
> >
> > Not knowing unplug well; can you just explain - is that device hard
> > unplugged and it's gone by the time this function returns or is
it still
> > hanging around for some indeterminate time?
Qemu will trigger an unplug request via pcie attention button in
which case
there could be a delay by the guest operating system. We could give
it some
amount of time and if nothing happens try surpise removal or handle the
error otherwise.
I'm missing something here:
Isn't the whole point of the new device-hiding infrastructure to
prevent QEMU from closing the VFIO until migration ended
successfully?
No. The point of hiding it is to only add the VFIO (that is configured
with the same MAC as the virtio-net device) until the
VIRTIO_NET_F_STANDBY feature is negotiated. We don't want to expose to
devices with the same MAC to guests who can't handle it.
What exactly is preventing QEMU from closing the host VFIO device
after the guest OS has handled the unplug request?
We qdev_unplug() the VFIO device and want the virtio-net standby device to
take over. If something goes wrong with unplug or
migration in general we have to qdev_plug() the device back.
This series does not try to implement new functionality to close a
device without freeing the resources.
From the discussion in this thread I understand that is what libvirt
needs though. Something that will trigger the unplug from the
guest but not free the devices resources in the host system (which is
what qdev_unplug() does). Correct?
Why is it bad to fully re-create the device in case of a failed migration?
I think the concern is that if the device was fully released by qemu
during migration, it might have already been given to some other/new
guest during the time that migration is trying to complete. If migration
then fails, you may be unable to restore the guest to the previous state.