Re: [Qemu-devel] [PATCH v4 1/1] vhost user: add support of live migration

[Linhaifeng <haifeng.lin@huawei.com>]

On 2015/7/10 21:05, Paolo Bonzini wrote:
>
> On 26/06/2015 11:22, Thibaut Collet wrote:
>> Some vhost client/backend 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 for RARP
>>     packets automatically send by qemu_announce_self after a migration.
>>     These packets are useless for vhost user and just discarded.
> When a packet is received by vhost-user, the vhost-user writes the
> packet in guest memory.  QEMU must then copy that page of guest memory
> from source to destination; it uses a dirty bitmap for this purpose.
>
> How does vhost-user do this?  I can see this patch providing enough
> support for *non*live migration.  However, it cannot be enough for live
> migration unless I'm missing something obvious.
>
> Paolo
Agree. vhost-user should mmap the log memory and mark dirty pages when 
send or receive packets.
>> Signed-off-by: Thibaut Collet <thibaut.collet@6wind.com>
>> ---
>>   hw/net/vhost_net.c |    2 ++
>>   net/vhost-user.c   |   21 +++++++++++++++++++--
>>   2 files changed, 21 insertions(+), 2 deletions(-)
>>
>> diff --git a/hw/net/vhost_net.c b/hw/net/vhost_net.c
>> index 9bd360b..668c422 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 b51bc04..20778a1 100644
>> --- a/net/vhost-user.c
>> +++ b/net/vhost-user.c
>> @@ -65,6 +65,24 @@ 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 of 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 receives unexpected packets\n");
>> +            fflush(stderr);
>> +            display_trace = 0;
>> +        }
>> +    }
>> +    return size;
>> +}
>> +
>>   static void vhost_user_cleanup(NetClientState *nc)
>>   {
>>       VhostUserState *s = DO_UPCAST(VhostUserState, nc, nc);
>> @@ -90,6 +108,7 @@ 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,
>> @@ -146,8 +165,6 @@ 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;
>>           s->nc.queue_index = i;
>>   
>>
>
>