Re: [Qemu-devel] [PATCH V7 0/5] Send the gratuitous by guest

[Michael S. Tsirkin]

On Thu, Mar 07, 2013 at 06:33:30PM +0800, Jason Wang wrote:
> On 03/07/2013 06:25 PM, Michael S. Tsirkin wrote:
> > On Thu, Mar 07, 2013 at 06:13:41PM +0800, Jason Wang wrote:
> >> On 03/07/2013 06:04 PM, Michael S. Tsirkin wrote:
> >>> On Thu, Mar 07, 2013 at 04:23:46PM +0800, Jason Wang wrote:
> >>>> This series tries to let guest instead of qemu to send the gratuitous 
> >>>> packets
> >>>> after migration when guest is capable of doing this. This is needed 
> >>>> since it's
> >>>> impossible for qemu to keep track of all configurations (e.g 802.1Q) and 
> >>>> mac
> >>>> addresses (more than one mac address may be used by guest). So qemu 
> >>>> can't build
> >>>> gratuitous packets for all those configurations properly. The only 
> >>>> solution is
> >>>> let guest driver who knew all needed information to do this.
> >>>>
> >>>> The series first introduces a new runstate which just tracks the state 
> >>>> when the
> >>>> migration is finished and guest is about to start. And then we can just 
> >>>> trying
> >>>> to notify the guest to send the GARP after changing from this state to
> >>>> running. A model specific announcing method were also also introduced to 
> >>>> let
> >>>> each kinds of nic do its own notification. When there's no such method 
> >>>> register
> >>>> for the nic, the old style of sending RARP were kept. And the last two 
> >>>> patches
> >>>> implemented the virtio-net method of notification.
> >>> Do we want to retry SELF_ANNOUNCE_ROUNDS?
> >> Yes, we do the announcement several times like in the past.
> >>>> Changes from V6:
> >>>> - introduce a new runstate instead of using a global variable check the 
> >>>> state
> >>>>
> >>>> Changes from V5:
> >>>> - use a global variable to decide whether an announcement is needed 
> >>>> after migration
> >>>> - align with virtio spec and let guest ack the announcement notification 
> >>>> through
> >>>>   control vq instead of config status writing
> >>>>
> >>>> Changes from V4:
> >>>> - keep the old behavior that send the gratuitous packets only after 
> >>>> migration
> >>> I wonder why it's a sane thing to do. How about simply sending the event 
> >>> after load?
> >> The aim is to limit the change of the behaviour to focus on migration.
> >> We may also need this after cont,
> > Hmm why after cont?
> 
> If we stop the vm for a long period, the mac will be missed in the
> forward table of the bridge also.

Hmm okay, needs some thought.

> >> and then maybe we can just do this
> >> unconditionally in vm_start().
> > OK but then the new infrastructure we are adding will be dead code,
> > won't it?
> 
> If we do this, there's no need to introduce a new state then.
> >
> > Can we do this simply using a post load hook for now?
> 
> Maybe not, this means we may want to inject an interrupt to guest when
> vm is not running.

What I'm suggesting is basically:
- set some per device flag on load
- announce based on vmstart if flag is set

We can drop the flag later if we want it on every vmstart.

> >>>> - decide whether to send gratuitous packets by previous runstate instead 
> >>>> of a dedicated parameter
> >>>> - check virtio_net_started() instead of VIRTIO_NET_S_LINK_UP before 
> >>>> issue the config update interrupt
> >>>> - move VIRTIO_NET_S_ANNOUNCE to 0x100 and supress guest config write to 
> >>>> RO bits
> >>>> - cleanups suggested by Michael
> >>>>
> >>>> Tested with migration within 802.1Q.
> >>>>
> >>>> Jason Wang (5):
> >>>>   runstate: introduce prelaunch-migrate state
> >>>>   net: announce self after vm is started
> >>>>   net: model specific announcing support
> >>>>   virtio-net: notify guest to annouce itself
> >>>>   virtio-net: compat guest announce
> >>>>
> >>>>  hw/pc.h           |    6 +++++-
> >>>>  hw/virtio-net.c   |   30 ++++++++++++++++++++++++++++++
> >>>>  hw/virtio-net.h   |   15 ++++++++++++++-
> >>>>  include/net/net.h |    2 ++
> >>>>  migration.c       |    4 +---
> >>>>  qapi-schema.json  |    5 ++++-
> >>>>  savevm.c          |    8 ++++++--
> >>>>  vl.c              |    8 +++++++-
> >>>>  8 files changed, 69 insertions(+), 9 deletions(-)