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Re: VIRTIO_NET_F_MTU not negotiated
From: |
Michael S. Tsirkin |
Subject: |
Re: VIRTIO_NET_F_MTU not negotiated |
Date: |
Wed, 27 Jul 2022 03:25:01 -0400 |
On Wed, Jul 27, 2022 at 06:51:56AM +0000, Eli Cohen wrote:
> I found out that the reason why I could not enforce the mtu stems from the
> fact that I did not configure max mtu for the net device (e.g. through
> libvirt <mtu size="9000"/>).
> Libvirt does not allow this configuration for vdpa devices and probably for a
> reason. The vdpa backend driver has the freedom to do it using its copy of
> virtio_net_config.
>
> The code in qemu that is responsible to allow to consider the device MTU
> restriction is here:
>
> static void virtio_net_device_realize(DeviceState *dev, Error **errp)
> {
> VirtIODevice *vdev = VIRTIO_DEVICE(dev);
> VirtIONet *n = VIRTIO_NET(dev);
> NetClientState *nc;
> int i;
>
> if (n->net_conf.mtu) {
> n->host_features |= (1ULL << VIRTIO_NET_F_MTU);
> }
>
> The above code can be interpreted as follows:
> if the command line arguments of qemu indicates that mtu should be limited,
> then we would read this mtu limitation from the device (that actual value is
> ignored).
>
> I worked around this limitation by unconditionally setting VIRTIO_NET_F_MTU
> in the host features. As said, it only indicates that we should read the
> actual limitation for the device.
>
> If this makes sense I can send a patch to fix this.
Well it will then either have to be for vdpa only, or have
compat machinery to avoid breaking migration.
--
MST
- RE: VIRTIO_NET_F_MTU not negotiated, Eli Cohen, 2022/07/27
- Re: VIRTIO_NET_F_MTU not negotiated,
Michael S. Tsirkin <=
- RE: VIRTIO_NET_F_MTU not negotiated, Eli Cohen, 2022/07/27
- Re: VIRTIO_NET_F_MTU not negotiated, Michael S. Tsirkin, 2022/07/27
- RE: VIRTIO_NET_F_MTU not negotiated, Eli Cohen, 2022/07/27
- Re: VIRTIO_NET_F_MTU not negotiated, Michael S. Tsirkin, 2022/07/27
- RE: VIRTIO_NET_F_MTU not negotiated, Eli Cohen, 2022/07/28
- Re: VIRTIO_NET_F_MTU not negotiated, Michael S. Tsirkin, 2022/07/28
Re: VIRTIO_NET_F_MTU not negotiated, Jason Wang, 2022/07/27