Subject: Re: [Xen-devel] [RFC PATCH 34/35] Add the Xen virtual network device driver.

From: Christian Limpach <[email-masked]>
Date: Tue, 9 May 2006 13:43:59 +0100

On Tue, May 09, 2006 at 09:55:33PM +1000, Herbert Xu wrote:
> Hi Chris:
> 
> Chris Wright <[email-masked]> wrote:
> >
> > +/** Send a packet on a net device to encourage switches to learn the
> > + * MAC. We send a fake ARP request.
> > + *
> > + * @param dev device
> > + * @return 0 on success, error code otherwise
> > + */
> > +static int send_fake_arp(struct net_device *dev)
> 
> I think we talked about this before.  I don't see why Xen is so special
> that it needs its own gratuitous arp routine embedded in the driver.
> If this is needed at all (presumably for migration) then it should be
> performed by the management scripts which can send grat ARP packets just
> as easily.

There's at least two reasons why having it in the driver is preferable:
- synchronizing sending the fake ARP request with when the device is
  operational -- you really want to make this well synchronized to keep
  unreachability as short as possible, especially when doing live
  migration
- anybody but the guest might not know (all) the MAC addresses for which
  to send a fake ARP request

    christian