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

[Linhaifeng]

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 <address@hidden>
> > ---
> >   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;
> >