Re: [PATCH v2 3/3] tun: Set num_buffers for virtio 1.0

Michael S. Tsirkin
2025-01-09T07:32:30Z

On Thu, Jan 09, 2025 at 03:58:45PM +0900, Akihiko Odaki wrote:
> The specification says the device MUST set num_buffers to 1 if
> VIRTIO_NET_F_MRG_RXBUF has not been negotiated.
>
> Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>

How do we know this is v1 and not v0? Confused.

> ---
> drivers/net/tap.c | 2 +-
> drivers/net/tun.c | 6 ++++--
> drivers/net/tun_vnet.c | 14 +++++++++-----
> drivers/net/tun_vnet.h | 4 ++--
> 4 files changed, 16 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/net/tap.c b/drivers/net/tap.c
> index 60804855510b..fe9554ee5b8b 100644
> --- a/drivers/net/tap.c
> +++ b/drivers/net/tap.c
> @@ -713,7 +713,7 @@ static ssize_t tap_put_user(struct tap_queue *q,
> int total;
>
> if (q->flags & IFF_VNET_HDR) {
> - struct virtio_net_hdr vnet_hdr;
> + struct virtio_net_hdr_v1 vnet_hdr;
>
> vnet_hdr_len = READ_ONCE(q->vnet_hdr_sz);
>
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index dbf0dee92e93..f211d0580887 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -1991,7 +1991,9 @@ static ssize_t tun_put_user_xdp(struct tun_struct *tun,
> size_t total;
>
> if (tun->flags & IFF_VNET_HDR) {
> - struct virtio_net_hdr gso = { 0 };
> + struct virtio_net_hdr_v1 gso = {
> + .num_buffers = __virtio16_to_cpu(true, 1)
> + };
>
> vnet_hdr_sz = READ_ONCE(tun->vnet_hdr_sz);
> ret = tun_vnet_hdr_put(vnet_hdr_sz, iter, &gso);
> @@ -2044,7 +2046,7 @@ static ssize_t tun_put_user(struct tun_struct *tun,
> }
>
> if (vnet_hdr_sz) {
> - struct virtio_net_hdr gso;
> + struct virtio_net_hdr_v1 gso;
>
> ret = tun_vnet_hdr_from_skb(tun->flags, tun->dev, skb, &gso);
> if (ret < 0)
> diff --git a/drivers/net/tun_vnet.c b/drivers/net/tun_vnet.c
> index ffb2186facd3..a7a7989fae56 100644
> --- a/drivers/net/tun_vnet.c
> +++ b/drivers/net/tun_vnet.c
> @@ -130,15 +130,17 @@ int tun_vnet_hdr_get(int sz, unsigned int flags, struct iov_iter *from,
> EXPORT_SYMBOL_GPL(tun_vnet_hdr_get);
>
> int tun_vnet_hdr_put(int sz, struct iov_iter *iter,
> - const struct virtio_net_hdr *hdr)
> + const struct virtio_net_hdr_v1 *hdr)
> {
> + int content_sz = MIN(sizeof(*hdr), sz);
> +
> if (iov_iter_count(iter) < sz)
> return -EINVAL;
>
> - if (copy_to_iter(hdr, sizeof(*hdr), iter) != sizeof(*hdr))
> + if (copy_to_iter(hdr, content_sz, iter) != content_sz)
> return -EFAULT;
>
> - if (iov_iter_zero(sz - sizeof(*hdr), iter) != sz - sizeof(*hdr))
> + if (iov_iter_zero(sz - content_sz, iter) != sz - content_sz)
> return -EFAULT;
>
> return 0;
> @@ -154,11 +156,11 @@ EXPORT_SYMBOL_GPL(tun_vnet_hdr_to_skb);
>
> int tun_vnet_hdr_from_skb(unsigned int flags, const struct net_device *dev,
> const struct sk_buff *skb,
> - struct virtio_net_hdr *hdr)
> + struct virtio_net_hdr_v1 *hdr)
> {
> int vlan_hlen = skb_vlan_tag_present(skb) ? VLAN_HLEN : 0;
>
> - if (virtio_net_hdr_from_skb(skb, hdr,
> + if (virtio_net_hdr_from_skb(skb, (struct virtio_net_hdr *)hdr,
> tun_vnet_is_little_endian(flags), true,
> vlan_hlen)) {
> struct skb_shared_info *sinfo = skb_shinfo(skb);
> @@ -176,6 +178,8 @@ int tun_vnet_hdr_from_skb(unsigned int flags, const struct net_device *dev,
> return -EINVAL;
> }
>
> + hdr->num_buffers = 1;
> +
> return 0;
> }
> EXPORT_SYMBOL_GPL(tun_vnet_hdr_from_skb);
> diff --git a/drivers/net/tun_vnet.h b/drivers/net/tun_vnet.h
> index 2dfdbe92bb24..d8fd94094227 100644
> --- a/drivers/net/tun_vnet.h
> +++ b/drivers/net/tun_vnet.h
> @@ -12,13 +12,13 @@ int tun_vnet_hdr_get(int sz, unsigned int flags, struct iov_iter *from,
> struct virtio_net_hdr *hdr);
>
> int tun_vnet_hdr_put(int sz, struct iov_iter *iter,
> - const struct virtio_net_hdr *hdr);
> + const struct virtio_net_hdr_v1 *hdr);
>
> int tun_vnet_hdr_to_skb(unsigned int flags, struct sk_buff *skb,
> const struct virtio_net_hdr *hdr);
>
> int tun_vnet_hdr_from_skb(unsigned int flags, const struct net_device *dev,
> const struct sk_buff *skb,
> - struct virtio_net_hdr *hdr);
> + struct virtio_net_hdr_v1 *hdr);
>
> #endif /* TUN_VNET_H */
>
> --
> 2.47.1