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

[Jason Wang]

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.
>> 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.
>>>> - 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(-)