[Qemu-devel] [V6 PATCH] virtio-net: send gratuitous packets when needed

[Jason Wang]

As hypervior does not have the knowledge of guest network configuration, it's
better to ask guest to send gratuitous packets when needed.

Guest tests VIRTIO_NET_S_ANNOUNCE bit during config change interrupt and when it
is set, a workqueue is scheduled to send gratuitous packet through
NETDEV_NOTIFY_PEERS. This feature is negotiated through bit
VIRTIO_NET_F_GUEST_ANNOUNCE.

Changes from v5:
- notify the chain before acking the link annoucement
- ack the link announcement notification through control vq

Changes from v4:
- typos
- handle workqueue unconditionally
- move VIRTIO_NET_S_ANNOUNCE to bit 8 to separate rw bits from ro bits

Changes from v3:
- cancel the workqueue during freeze

Changes from v2:
- fix the race between unregister_dev() and workqueue

Signed-off-by: Jason Wang <address@hidden>
---
 drivers/net/virtio_net.c   |   32 +++++++++++++++++++++++++++++++-
 include/linux/virtio_net.h |   13 +++++++++++++
 2 files changed, 44 insertions(+), 1 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 4880aa8..0f60da7 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -72,6 +72,9 @@ struct virtnet_info {
        /* Work struct for refilling if we run low on memory. */
        struct delayed_work refill;
 
+       /* Work struct for sending gratuitous packets. */
+       struct work_struct announce;
+
        /* Chain pages by the private ptr. */
        struct page *pages;
 
@@ -781,12 +784,30 @@ static bool virtnet_send_command(struct virtnet_info *vi, 
u8 class, u8 cmd,
        return status == VIRTIO_NET_OK;
 }
 
+static void virtnet_ack_link_announce(struct virtnet_info *vi)
+{
+       if (!virtnet_send_command(vi, VIRTIO_NET_CTRL_ANNOUNCE,
+                                 VIRTIO_NET_CTRL_ANNOUNCE_ACK, NULL,
+                                 0, 0)) {
+               dev_warn(&vi->dev->dev, "Failed to ack link nnounce.\n");
+       }
+}
+
+static void announce_work(struct work_struct *work)
+{
+       struct virtnet_info *vi = container_of(work, struct virtnet_info,
+                                              announce);
+       netif_notify_peers(vi->dev);
+       virtnet_ack_link_announce(vi);
+}
+
 static int virtnet_close(struct net_device *dev)
 {
        struct virtnet_info *vi = netdev_priv(dev);
 
        /* Make sure refill_work doesn't re-enable napi! */
        cancel_delayed_work_sync(&vi->refill);
+       cancel_work_sync(&vi->announce);
        napi_disable(&vi->napi);
 
        return 0;
@@ -962,11 +983,17 @@ static void virtnet_update_status(struct virtnet_info *vi)
                return;
 
        /* Ignore unknown (future) status bits */
-       v &= VIRTIO_NET_S_LINK_UP;
+       v &= VIRTIO_NET_S_LINK_UP | VIRTIO_NET_S_ANNOUNCE;
 
        if (vi->status == v)
                return;
 
+       if (v & VIRTIO_NET_S_ANNOUNCE) {
+               v &= ~VIRTIO_NET_S_ANNOUNCE;
+               if (v & VIRTIO_NET_S_LINK_UP)
+                       schedule_work(&vi->announce);
+       }
+
        vi->status = v;
 
        if (vi->status & VIRTIO_NET_S_LINK_UP) {
@@ -1076,6 +1103,7 @@ static int virtnet_probe(struct virtio_device *vdev)
                goto free;
 
        INIT_DELAYED_WORK(&vi->refill, refill_work);
+       INIT_WORK(&vi->announce, announce_work);
        sg_init_table(vi->rx_sg, ARRAY_SIZE(vi->rx_sg));
        sg_init_table(vi->tx_sg, ARRAY_SIZE(vi->tx_sg));
 
@@ -1187,6 +1215,7 @@ static int virtnet_freeze(struct virtio_device *vdev)
        virtqueue_disable_cb(vi->svq);
        if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_CTRL_VQ))
                virtqueue_disable_cb(vi->cvq);
+       cancel_work_sync(&vi->announce);
 
        netif_device_detach(vi->dev);
        cancel_delayed_work_sync(&vi->refill);
@@ -1233,6 +1262,7 @@ static unsigned int features[] = {
        VIRTIO_NET_F_GUEST_ECN, VIRTIO_NET_F_GUEST_UFO,
        VIRTIO_NET_F_MRG_RXBUF, VIRTIO_NET_F_STATUS, VIRTIO_NET_F_CTRL_VQ,
        VIRTIO_NET_F_CTRL_RX, VIRTIO_NET_F_CTRL_VLAN,
+       VIRTIO_NET_F_GUEST_ANNOUNCE,
 };
 
 static struct virtio_driver virtio_net_driver = {
diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h
index 970d5a2..383e8a0 100644
--- a/include/linux/virtio_net.h
+++ b/include/linux/virtio_net.h
@@ -49,8 +49,10 @@
 #define VIRTIO_NET_F_CTRL_RX   18      /* Control channel RX mode support */
 #define VIRTIO_NET_F_CTRL_VLAN 19      /* Control channel VLAN filtering */
 #define VIRTIO_NET_F_CTRL_RX_EXTRA 20  /* Extra RX mode control support */
+#define VIRTIO_NET_F_GUEST_ANNOUNCE 21  /* Guest can send gratituous packet */
 
 #define VIRTIO_NET_S_LINK_UP   1       /* Link is up */
+#define VIRTIO_NET_S_ANNOUNCE   2      /* Announcement is needed */
 
 struct virtio_net_config {
        /* The config defining mac address (if VIRTIO_NET_F_MAC) */
@@ -152,4 +154,15 @@ struct virtio_net_ctrl_mac {
  #define VIRTIO_NET_CTRL_VLAN_ADD             0
  #define VIRTIO_NET_CTRL_VLAN_DEL             1
 
+/*
+ * Control link announce acknowledgement
+ *
+ * The command VIRTIO_NET_CTRL_ANNOUNCE_ACK is used to indicate that
+ * driver has recevied the notification and device would clear the
+ * VIRTIO_NET_S_ANNOUNCE bit in the status filed after it received
+ * this command.
+ */
+#define VIRTIO_NET_CTRL_ANNOUNCE       3
+ #define VIRTIO_NET_CTRL_ANNOUNCE_ACK         0
+
 #endif /* _LINUX_VIRTIO_NET_H */