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 09:55:02AM +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.
> >
> Could you make a statement for 'retry several times' ?
> Is it the process of retrying several times to sending RARP in qemu_announce_self_once?

yes

> 'broadcast the RARP with current MAC in NIC's migration load handler respectively' is distributing the job of what qemu_announce_self does to every NIC's migration load handler, 
> e.g., in virtio NIC's migration load handler virtio_net_load, we can create a timer to retry several times to send ARAP with current MAC for this NIC, just as same as qemu_announce_self does.

I don't see a lot of value in this yet.

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