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

[Thibaut Collet]

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;
+}
+
 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