Good to see this discussion going. I share the same feeling that the decision of plugging the primary (passthrough) should only be made until guest driver acknowledges DRIVER_OK and _F_STANDBY. Architecturally this intelligence should be baken to QEMU itself rather than moving up to management stack, such as libvirt. A few questions in line below. On Tue, Jun 5, 2018 at 5:33 AM, Michael S. Tsirkin <mst@xxxxxxxxxx> wrote: > I don't think this is sufficient. > > If both primary and standby devices are present, a legacy guest without > support for the feature might see two devices with same mac and get > confused. > > I think that we should only make primary visible after guest acked the > backup feature bit. > > And on reset or when backup is cleared in some other way, unplug the > primary. > > Something like the below will do the job: > > Primary device is added with a special "primary-failover" flag. I wonder if you envision this flag as a user interface or some internal attribute/property to QEMU device? Since QEMU needs to associate this particular primary-failover device with a virtio standby instance for checking DRIVER_OK as you indicate below, I wonder if the group ID thing will be helpful to set "primary-failover" flag internally without having to add another option in CLI? > A virtual machine is then initialized with just a standby virtio > device. Primary is not yet added. > > Later QEMU detects that guest driver device set DRIVER_OK. > It then exposes the primary device to the guest, and triggers > a device addition event (hot-plug event) for it. Sounds OK. While there might be a small window the guest already starts to use virtio interface before the passthrough gets plugged in, I think that should be fine. Another option is to wait until the primary appears and gets registered in the guest, so it can bring up the upper failover interface. > > If QEMU detects guest driver removal, it initiates a hot-unplug sequence > to remove the primary driver. In particular, if QEMU detects guest > re-initialization (e.g. by detecting guest reset) it immediately removes > the primary device. Agreed. For legacy guest, user might prefer seeing a single passthrough device rather than a virtio device. I would hope there's an option to allow it to happen, instead of removing all passthrough devices. Regards, -Siwei > > We can move some of this code to management as well, architecturally it > does not make too much sense but it might be easier implementation-wise. > > HTH > > On Mon, Jun 04, 2018 at 06:41:48PM -0700, Samudrala, Sridhar wrote: >> Ping on this patch now that the kernel patches are accepted into davem's net-next tree. >> https://patchwork.ozlabs.org/cover/920005/ >> >> >> On 5/7/2018 4:09 PM, Sridhar Samudrala wrote: >> > This feature bit can be used by hypervisor to indicate virtio_net device to >> > act as a standby for another device with the same MAC address. >> > >> > I tested this with a small change to the patch to mark the STANDBY feature 'true' >> > by default as i am using libvirt to start the VMs. >> > Is there a way to pass the newly added feature bit 'standby' to qemu via libvirt >> > XML file? >> > >> > Signed-off-by: Sridhar Samudrala <sridhar.samudrala@xxxxxxxxx> >> > --- >> > hw/net/virtio-net.c | 2 ++ >> > include/standard-headers/linux/virtio_net.h | 3 +++ >> > 2 files changed, 5 insertions(+) >> > >> > diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c >> > index 90502fca7c..38b3140670 100644 >> > --- a/hw/net/virtio-net.c >> > +++ b/hw/net/virtio-net.c >> > @@ -2198,6 +2198,8 @@ static Property virtio_net_properties[] = { >> > true), >> > DEFINE_PROP_INT32("speed", VirtIONet, net_conf.speed, SPEED_UNKNOWN), >> > DEFINE_PROP_STRING("duplex", VirtIONet, net_conf.duplex_str), >> > + DEFINE_PROP_BIT64("standby", VirtIONet, host_features, VIRTIO_NET_F_STANDBY, >> > + false), >> > DEFINE_PROP_END_OF_LIST(), >> > }; >> > diff --git a/include/standard-headers/linux/virtio_net.h b/include/standard-headers/linux/virtio_net.h >> > index e9f255ea3f..01ec09684c 100644 >> > --- a/include/standard-headers/linux/virtio_net.h >> > +++ b/include/standard-headers/linux/virtio_net.h >> > @@ -57,6 +57,9 @@ >> > * Steering */ >> > #define VIRTIO_NET_F_CTRL_MAC_ADDR 23 /* Set MAC address */ >> > +#define VIRTIO_NET_F_STANDBY 62 /* Act as standby for another device >> > + * with the same MAC. >> > + */ >> > #define VIRTIO_NET_F_SPEED_DUPLEX 63 /* Device set linkspeed and duplex */ >> > #ifndef VIRTIO_NET_NO_LEGACY > > --------------------------------------------------------------------- > To unsubscribe, e-mail: virtio-dev-unsubscribe@xxxxxxxxxxxxxxxxxxxx > For additional commands, e-mail: virtio-dev-help@xxxxxxxxxxxxxxxxxxxx > _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
