Re: [xen-4.0-testing test] 2045: regressions - FAIL

["Jan Beulich" <JBeulich@novell.com>]

>>> On 31.08.10 at 17:05, Ian Campbell <Ian.Campbell@eu.citrix.com> wrote:
> On Tue, 2010-08-31 at 15:35 +0100, Ian Jackson wrote:
>> 
>> > Even with the fix in place the gratuitous ARP behaviour is disabled
>> by
>> > default so you need to enable the net.ipv4.conf.<dev>.arp_notify
>> sysctl
>> > for any device you want to send the notifications. When I was
>> testing I
>> > did this by adding
>> >         net.ipv4.conf.default.arp_notify = 1
>> > to /etc/sysctl.conf and that seemed to do the trick.
>> 
>> I think this is a bug.  I think the default should be for something to
>> send this gratuitous arp and the most logical answer in the PV or
>> PV-on-HVM case is the domU.
> 
> This is the upstream default, not something we control directly from
> netfront etc.

Wouldn't it seem possible/reasonable to force this on from netfront
(via IN_DEV_CONF_SET()) at least until upstream possibly decides
to not let the ARP_NOTIFY sysctl control the sending of an ARP
explicitly requested through netif_notify_peers()?

The perhaps undesirable effect of this (as well as setting the sysctl
through /etc/sysctl.conf) is that it doesn't only control the ARP we
want sent, but also one when bringing the interface up or changing
its address, so I'd still favor moving the NETDEV_NOTIFY_PEERS
case past the "if (IN_DEV_ARP_NOTIFY(in_dev))" in inetdev_event().
Have you got any feedback from Linux folks on such a potential
change?

Jan