Re: [Qemu-devel] [PATCH 1/2] avoid to allcate used macaddr to to new nic

[Fam Zheng]

On Mon, 06/17 17:00, Michael S. Tsirkin wrote:
> On Mon, Jun 17, 2013 at 09:35:10PM +0800, Amos Kong wrote:
> > QEMU allocates macaddr to nic if user doesn't assigne macaddr.
> > But we didn't check if the allocated macaddr is used, it might
> > cause macaddr repeated.
> > 
> >  # qemu -device e1000,netdev=h1,mac=52:54:00:12:34:56
> >   (qemu) device_add e1000
> >   (qemu) info network
> >   e1000.0: index=0,type=nic,model=e1000,macaddr=52:54:00:12:34:56
> >    \ h1: index=0,type=user,net=10.0.2.0,restrict=off
> >   e1000.1: index=0,type=nic,model=e1000,macaddr=52:54:00:12:34:56
> > 
> > This patch adds a check in allocating macaddr, reallocate macaddr
> > if it's used by other nic.
> > 
> > Signed-off-by: Amos Kong <address@hidden>
> 
> I'm not sure this is not exactly what was intended in this case.
> Also this ptotects against an unlikely case of mixing
> implicit and explicit addresses, but not against
> a likely case of multiple qemu on same LAN using same MAC.

IMHO, either way we can do little to protect against collision of
multiple qemu on the same LAN, but at least this patch protects against
repeated MAC address in one qemu instance. Better in some degree.

Leaving it to user, and asking for address explictly, absolutely helps,
but makes the interface a bit harder to use: there are still cases user
wants it generated automatically.

Just wondering if a random one could be better?

-- 
Fam