Quoting Sameeh Jubran (2018-10-25 13:01:10)
On Thu, Oct 25, 2018 at 5:06 PM Sameeh Jubran <sameeh@daynix.com> wrote:
From: Sameeh Jubran <sjubran@redhat.com>
Hi all,
Background:
There has been a few attempts to implement the standby feature for vfio assigned devices which aims to enable the migration of such devices. This is another attempt.
The series implements an infrastructure for hiding devices from the bus upon boot. What it does is the following:
* In the first patch the infrastructure for hiding the device is added for the qbus and qdev APIs. A "hidden" boolean is added to the device state and it is set based on a callback to the standby device which registers itself for handling the assessment: "should the primary device be hidden?" by cross validating the ids of the devices.
* In the second patch the virtio-net uses the API to hide the vfio device and unhides it when the feature is acked.
Disclaimers:
* I have only scratch tested this and from qemu side, it seems to be working. * This is an RFC so it lacks some proper error handling in few cases and proper resource freeing. I wanted to get some feedback first before it is finalized.
Command line example:
/home/sameeh/Builds/failover/qemu/x86_64-softmmu/qemu-system-x86_64 \ -netdev tap,id=hostnet0,script=world_bridge_standalone.sh,downscript=no,ifname=cc1_71 \ -netdev tap,vhost=on,id=hostnet1,script=world_bridge_standalone.sh,downscript=no,ifname=cc1_72,queues=4 \ -device virtio-net,host_mtu=1500,netdev=hostnet1,id=cc1_72,vectors=10,mq=on,primary=cc1_71 \ -device e1000,netdev=hostnet0,id=cc1_71,standby=cc1_72 \
Migration support:
Pre migration or during setup phase of the migration we should send an unplug request to the guest to unplug the primary device. I haven't had the chance to implement that part yet but should do soon. Do you know what's the best approach to do so? I wanted to have a callback to the virtio-net device which tries to send an unplug request to the guest and if succeeds then the migration continues. It needs to handle the case where the migration fails and then it has to replug the primary device back.
I think that the "add_migration_state_change_notifier" API call can be used from within the virtio-net device to achieve this, what do you think?
I think it would be good to hear from the libvirt folks (on Cc:) on this as having QEMU unplug a device without libvirt's involvement seems like it could cause issues. Personally I think it seems cleaner to just have QEMU handle the 'hidden' aspects of the device and leave it to QMP/libvirt to do the unplug beforehand. On the libvirt side I could imagine adding an option like virsh migrate --switch-to-standby-networking or something along that line to do it automatically (if we decide doing it automatically is even needed on that end).
The following terms are used as interchangeable: standby - virtio-net primary - vfio-device - physical device - assigned device
Please share your thoughts and suggestions, Thanks!
Sameeh Jubran (2): qdev/qbus: Add hidden device support virtio-net: Implement VIRTIO_NET_F_STANDBY feature
hw/core/qdev.c | 48 +++++++++++++++++++++++++--- hw/net/virtio-net.c | 25 +++++++++++++++ hw/pci/pci.c | 1 + include/hw/pci/pci.h | 2 ++ include/hw/qdev-core.h | 11 ++++++- include/hw/virtio/virtio-net.h | 5 +++ qdev-monitor.c | 58 ++++++++++++++++++++++++++++++++-- 7 files changed, 142 insertions(+), 8 deletions(-)
-- 2.17.0
-- Respectfully, Sameeh Jubran Linkedin Software Engineer @ Daynix.