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 <thibaut.col...@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;