Re: [Qemu-devel] [PATCH v5 1/2] vhost user: add support of live migration

[Thibaut Collet]

On Tue, Aug 4, 2015 at 7:50 PM, Marc-André Lureau
<address@hidden> wrote:
> Hi Thibaut
>
> On Mon, Aug 3, 2015 at 11:22 AM, Thibaut Collet
> <address@hidden> wrote:
>> Some vhost user backends are able to support live migration.
>> To provide this service the following features must be added:
>> 1. Add the VIRTIO_NET_F_GUEST_ANNOUNCE capability to vhost-net when netdev
>>    backend is vhost-user.
>> 2. Provide a nop receive callback to vhost-user.
>>    This callback is used only by qemu_announce_self after a migration to send
>>    fake RARP to avoid network outage for peers talking to the migrated guest.
>>    - For guest with GUEST_ANNOUNCE capabilities these packets must be 
>> discarded,
>>      GARP are sent by the guest thanks the GUEST_ANNOUNCE.
>>    - For guest without GUEST_ANNOUNCE capabilities these packets are 
>> discarded
>>      too, migration termination is notified when the guest sends packets.
>>
>> Signed-off-by: Thibaut Collet <address@hidden>
>> ---
>>  hw/net/vhost_net.c |    2 ++
>>  net/vhost-user.c   |   25 +++++++++++++++++++++++--
>>  2 files changed, 25 insertions(+), 2 deletions(-)
>>
>> diff --git a/hw/net/vhost_net.c b/hw/net/vhost_net.c
>> index c864237..9850520 100644
>> --- a/hw/net/vhost_net.c
>> +++ b/hw/net/vhost_net.c
>> @@ -85,6 +85,8 @@ static const int user_feature_bits[] = {
>>      VIRTIO_NET_F_CTRL_MAC_ADDR,
>>      VIRTIO_NET_F_CTRL_GUEST_OFFLOADS,
>>
>> +    VIRTIO_NET_F_GUEST_ANNOUNCE,
>> +
>>      VIRTIO_NET_F_MQ,
>>
>>      VHOST_INVALID_FEATURE_BIT
>> diff --git a/net/vhost-user.c b/net/vhost-user.c
>> index 93dcecd..2290271 100644
>> --- a/net/vhost-user.c
>> +++ b/net/vhost-user.c
>> @@ -65,6 +65,28 @@ static void vhost_user_stop(VhostUserState *s)
>>      s->vhost_net = 0;
>>  }
>>
>> +static ssize_t vhost_user_receive(NetClientState *nc, const uint8_t *buf,
>> +                                  size_t size)
>> +{
>> +    /* A live migration is done. Display an error if the packet is not a 
>> RARP.
>> +     * RARP are just discarded: guest is already notified about live 
>> migration
>> +     * by the virtio-net NIC or by the vhost-user backend.
>> +     */
>> +    if (size != 60) {
>> +        static int display_trace = 1;
>> +
>> +        if (display_trace) {
>> +            fprintf(stderr,
>> +                    "Vhost user expects only RARP (size 60)."
>> +                    "Receives unexpected packets with size %lu\n",
>> +                    size);
>> +            fflush(stderr);
>> +            display_trace = 0;
>> +        }
>> +    }
>> +    return size;
>> +}
>
> This warning appears during a dummy boot with vapp: qemu-system-x86_64
> -m 512 -object 
> memory-backend-file,id=mem,size=512M,mem-path=/hugetlbfs/,share=on
> -numa node,memdev=mem -netdev
> vhost-user,id=net0,chardev=chr0,vhostforce -device
> virtio-net-pci,netdev=net0 -chardev
> socket,id=chr0,path=/tmp/vapp.sock.
>
> I think silentely returning 0 (without warning) is the right way to
> keep the packets queued in the ring instead. But I must say I am quite
> confused as this is triggered by a VIRTIO_PCI_QUEUE_NOTIFY ioport
> write, and I fail to see how vhost-user handles it then without
> eventfd kick...
>
>>  static void vhost_user_cleanup(NetClientState *nc)
>>  {
>>      VhostUserState *s = DO_UPCAST(VhostUserState, nc, nc);
>> @@ -90,6 +112,7 @@ static bool vhost_user_has_ufo(NetClientState *nc)
>>  static NetClientInfo net_vhost_user_info = {
>>          .type = NET_CLIENT_OPTIONS_KIND_VHOST_USER,
>>          .size = sizeof(VhostUserState),
>> +        .receive = vhost_user_receive,
>>          .cleanup = vhost_user_cleanup,
>>          .has_vnet_hdr = vhost_user_has_vnet_hdr,
>>          .has_ufo = vhost_user_has_ufo,
>> @@ -143,8 +166,6 @@ static int net_vhost_user_init(NetClientState *peer, 
>> const char *device,
>>
>>      s = DO_UPCAST(VhostUserState, nc, nc);
>>
>> -    /* We don't provide a receive callback */
>> -    s->nc.receive_disabled = 1;
>>      s->chr = chr;
>>
>>      qemu_chr_add_handlers(s->chr, NULL, NULL, net_vhost_user_event, s);
>> --
>> 1.7.10.4
>>
>
>
>
> --
> Marc-André Lureau

Hi,

I have reproduced the issue and the message receive by vhost-user is
quite strange: this message is a virtio header plus a bootp/dhcp
request (I do not understand why there are the virtio header)
With a dummy boot, vhost user backend already receives 4 bootp/dhcp
requests form the bios guest so I do not see any interest to transmit
this request to vhostuser backend.

I suggest to remove the warning and discard the dhcp/bootp request (it
is useless to duplicate bootp/dhcp request)


Thibaut.