Re: [Qemu-devel] [RFC v3 2/3] vhost-net: Notify the backend about the host MTU

[Maxime Coquelin]

On 12/06/2016 07:31 PM, Aaron Conole wrote:

Maxime Coquelin <maxime.coque...@redhat.com> writes:

This patch provides a way for virtio-net to notify the
backend about the host MTU set by the user.

Cc: Michael S. Tsirkin <m...@redhat.com>
Cc: Aaron Conole <acon...@redhat.com>
Signed-off-by: Maxime Coquelin <maxime.coque...@redhat.com>
---
 hw/net/vhost_net.c      | 22 ++++++++++++++++++++++
 include/net/vhost_net.h |  2 ++
 2 files changed, 24 insertions(+)

diff --git a/hw/net/vhost_net.c b/hw/net/vhost_net.c
index f2d49ad..d7c13d4 100644
--- a/hw/net/vhost_net.c
+++ b/hw/net/vhost_net.c
@@ -51,6 +51,7 @@ static const int kernel_feature_bits[] = {
     VIRTIO_RING_F_EVENT_IDX,
     VIRTIO_NET_F_MRG_RXBUF,
     VIRTIO_F_VERSION_1,
+    VIRTIO_NET_F_MTU,
     VHOST_INVALID_FEATURE_BIT
 };

@@ -74,6 +75,7 @@ static const int user_feature_bits[] = {
     VIRTIO_NET_F_HOST_ECN,
     VIRTIO_NET_F_HOST_UFO,
     VIRTIO_NET_F_MRG_RXBUF,
+    VIRTIO_NET_F_MTU,

     /* This bit implies RARP isn't sent by QEMU out of band */
     VIRTIO_NET_F_GUEST_ANNOUNCE,
@@ -435,6 +437,22 @@ int vhost_set_vring_enable(NetClientState *nc, int enable)
     return 0;
 }

+int vhost_net_set_mtu(struct vhost_net *net, uint16_t mtu)
+{
+    const VhostOps *vhost_ops = net->dev.vhost_ops;
+    int ret;
+
+    if (!vhost_ops->vhost_net_set_mtu) {
+        return -ENOSYS;
+    }
+
+    ret = vhost_ops->vhost_net_set_mtu(&net->dev, mtu);
+    if (ret < 0) {
+        return -errno;
+    }
+    return 0;
+}
+
 #else
 uint64_t vhost_net_get_max_queues(VHostNetState *net)
 {
@@ -501,4 +519,8 @@ int vhost_set_vring_enable(NetClientState *nc, int enable)
 {
     return 0;
 }
+
+int vhost_net_set_mtu(struct vhost_net *net, uint16_t mtu)
+{
+}
 #endif

I think this should return something - I don't know what value will come
through if it doesn't :).

Good catch, of course something should be returned...

Thanks!
Maxime