Re: [Qemu-devel] [RFC] sync NIC's MAC maintained in NICConf as soon as emualted NIC's MAC changed in guest

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Sep 25, 2013 at 09:02:54AM +0000, Zhanghaoyu (A) wrote:
> >> Hi, all
> >> 
> >> Do live migration if emulated NIC's MAC has been changed, RARP with 
> >> wrong MAC address will broadcast via qemu_announce_self in destination, so, long time network disconnection probably happen.
> >
> >Good catch.
> >
> >> I want to do below works to resolve this problem, 1. change NICConf's 
> >> MAC as soon as emulated NIC's MAC changed in guest
> >
> >This will make it impossible to revert it correctly on reset, won't it?
> >
> You are right.
> virsh reboot <domain>, or virsh reset <domain>, or reboot VM from guest, will revert emulated NIC's MAC to original one maintained in NICConf.
> During the reboot/reset flow in qemu, emulated NIC's reset handler will sync the MAC address in NICConf to the MAC address in emulated NIC structure,
> e.g., virtio_net_reset sync the MAC address in NICConf to VirtIONet'mac.
> 
> BTW, in native scenario, reboot will revert the changed MAC to original one, too.
> 
> >> 2. sync NIC's (more precisely, queue) MAC to corresponding NICConf in 
> >> NIC's migration load handler
> >> 
> >> Any better ideas?
> >> 
> >> Thanks,
> >> Zhang Haoyu
> >
> >I think announce needs to poke at the current MAC instead of the default one in NICConf.
> >We can make it respect link down state while we are at it.
> >
> NICConf structures are incorporated in different emulated NIC's structure, e.g., VirtIONet, E1000State_st, RTL8139State, etc.,
> since so many kinds of emulated NICs, they are described by different structures, how to find all NICs' current MAC?
> 
> Maybe we can introduce a pointer member 'current_mac' to NICConf structure, which points to the current MAC,
> then we can find all current MACs from NICConf.current_mac.

I wouldn't make it a pointer, just a buffer with the mac, copy it there.
Maybe call it "softmac" that's what it is really.

> Can we broadcast the RARP with current MAC in NIC's migration load handler respectively?
> 
> Thanks,
> Zhang Haoyu

It's not so simple, you need to retry several times.

> >Happily recent linux guests aren't affected since they do announcements from guest.
> >
> >--
> >MST