netdev - Re: [Qemu-devel] [RFC v2 PATCH 5/4 PATCH] virtio-net: send gratuitous packet when needed

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Date:	Mon, 24 Oct 2011 11:11:05 +0200
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
CC:	Rusty Russell <rusty@...tcorp.com.au>,
	Jason Wang <jasowang@...hat.com>, <aliguori@...ibm.com>,
	<quintela@...hat.com>, <jan.kiszka@...mens.com>,
	<qemu-devel@...gnu.org>, <blauwirbel@...il.com>,
	<pbonzini@...hat.com>, <kvm@...r.kernel.org>,
	<netdev@...r.kernel.org>
Subject: Re: [Qemu-devel] [RFC v2 PATCH 5/4 PATCH] virtio-net: send
 gratuitous packet when needed

On Mon, 2011-10-24 at 07:25 +0200, Michael S. Tsirkin wrote:
> On Mon, Oct 24, 2011 at 02:54:59PM +1030, Rusty Russell wrote:
> > On Sat, 22 Oct 2011 13:43:11 +0800, Jason Wang <jasowang@...hat.com> wrote:
> > > This make let virtio-net driver can send gratituous packet by a new
> > > config bit - VIRTIO_NET_S_ANNOUNCE in each config update
> > > interrupt. When this bit is set by backend, the driver would schedule
> > > a workqueue to send gratituous packet through NETDEV_NOTIFY_PEERS.
> > > 
> > > This feature is negotiated through bit VIRTIO_NET_F_GUEST_ANNOUNCE.
> > > 
> > > Signed-off-by: Jason Wang <jasowang@...hat.com>
> > 
> > This seems like a huge layering violation.  Imagine this in real
> > hardware, for example.
> 
> commits 06c4648d46d1b757d6b9591a86810be79818b60c
> and 99606477a5888b0ead0284fecb13417b1da8e3af
> document the need for this:
> 
> NETDEV_NOTIFY_PEERS notifier indicates that a device moved to a 
> different physical link.
> 	and
> In real hardware such notifications are only
> generated when the device comes up or the address changes.
> 
> So hypervisor could get the same behaviour by sending link up/down
> events, this is just an optimization so guest won't do
> unecessary stuff like try to reconfigure an IP address.
> 
> 
> Maybe LOCATION_CHANGE would be a better name?
[...]

We also use this in bonding failover, where the system location doesn't
change but a different link is used.  However, I do recognise that the
name ought to indicate what kind of change happened and not what the
expected action is.

Ben.

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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