netdev - Re: [PATCH 1/4] virtio-net: add definitions for host USO feature

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Date:   Tue, 11 May 2021 11:12:16 +0300
From:   Yuri Benditovich <yuri.benditovich@...nix.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        "Michael S . Tsirkin" <mst@...hat.com>,
        Network Development <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        virtualization@...ts.linux-foundation.org,
        Yan Vugenfirer <yan@...nix.com>
Subject: Re: [PATCH 1/4] virtio-net: add definitions for host USO feature

On Tue, May 11, 2021 at 9:47 AM Jason Wang <jasowang@...hat.com> wrote:
>
>
> 在 2021/5/11 下午12:42, Yuri Benditovich 写道:
> > Define feature bit and GSO type according to the VIRTIO
> > specification.
> >
> > Signed-off-by: Yuri Benditovich <yuri.benditovich@...nix.com>
> > ---
> >   include/uapi/linux/virtio_net.h | 2 ++
> >   1 file changed, 2 insertions(+)
> >
> > diff --git a/include/uapi/linux/virtio_net.h b/include/uapi/linux/virtio_net.h
> > index 3f55a4215f11..a556ac735d7f 100644
> > --- a/include/uapi/linux/virtio_net.h
> > +++ b/include/uapi/linux/virtio_net.h
> > @@ -57,6 +57,7 @@
> >                                        * Steering */
> >   #define VIRTIO_NET_F_CTRL_MAC_ADDR 23       /* Set MAC address */
> >
> > +#define VIRTIO_NET_F_HOST_USO     56 /* Host can handle USO packets */

This is the virtio-net feature

> >   #define VIRTIO_NET_F_HASH_REPORT  57        /* Supports hash report */
> >   #define VIRTIO_NET_F_RSS      60    /* Supports RSS RX steering */
> >   #define VIRTIO_NET_F_RSC_EXT          61    /* extended coalescing info */
> > @@ -130,6 +131,7 @@ struct virtio_net_hdr_v1 {
> >   #define VIRTIO_NET_HDR_GSO_TCPV4    1       /* GSO frame, IPv4 TCP (TSO) */
> >   #define VIRTIO_NET_HDR_GSO_UDP              3       /* GSO frame, IPv4 UDP (UFO) */
> >   #define VIRTIO_NET_HDR_GSO_TCPV6    4       /* GSO frame, IPv6 TCP */
> > +#define VIRTIO_NET_HDR_GSO_UDP_L4    5       /* GSO frame, IPv4 UDP (USO) */

This is respective GSO type

>
>
> This is the gso_type not the feature actually.
>
> I wonder what's the reason for not
>
> 1) introducing a dedicated virtio-net feature bit for this
> (VIRTIO_NET_F_GUEST_GSO_UDP_L4.

This series is not for GUEST's feature, it is only for host feature.

> 2) toggle the NETIF_F_GSO_UDP_L4  feature for tuntap based on the
> negotiated feature.

The NETIF_F_GSO_UDP_L4 would be required for the guest RX path.
The guest TX path does not require any flags to be propagated, it only
allows the guest to transmit large UDP packets and have them
automatically splitted.
(This is similar to HOST_UFO but does packet segmentation instead of
fragmentation. GUEST_UFO indeed requires a respective NETIF flag, as
it is unclear whether the guest is capable of receiving such packets).

>
> Thanks
>
>
> >   #define VIRTIO_NET_HDR_GSO_ECN              0x80    /* TCP has ECN set */
> >       __u8 gso_type;
> >       __virtio16 hdr_len;     /* Ethernet + IP + tcp/udp hdrs */
>