Subject: Re: [PATCH RFC v2 1/2] tun: support rx-tstamp

From: Willem de Bruijn <[email-masked]>
Date: Sun, 01 Feb 2026 16:00:49 -0500

Steffen Trumtrar wrote:
> Demonstrate support for new virtio-net features
> 
> VIRTIO_NET_HDR_F_TSTAMP
> 
> This is not intended to be merged.
> 
> A full feature test also requires a patched qemu binary that knows
> these features and negotiates correct vnet_hdr_sz in
> virtio_net_set_mrg_rx_bufs. See
> https://github.com/strumtrar/qemu/tree/v10.2.0/virtio-rx-stamps
> 
> Not-yet-signed-off-by: Steffen Trumtrar <[email-masked]>
> ---
>  drivers/net/tun.c | 30 ++++++++++++++++++------------
>  1 file changed, 18 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index 8192740357a09..aa988a9c4bc99 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -2065,23 +2065,29 @@ static ssize_t tun_put_user(struct tun_struct *tun,
>  	}
>  
>  	if (vnet_hdr_sz) {
> -		struct virtio_net_hdr_v1_hash_tunnel hdr;
> -		struct virtio_net_hdr *gso;
> +		struct virtio_net_hdr_v1_hash_tunnel_ts hdr;

This patch refers to a struct that does not exist yet, so this cannot
compile?

> +
> +		memset(&hdr, 0, sizeof(hdr));
>  
>  		ret = tun_vnet_hdr_tnl_from_skb(tun->flags, tun->dev, skb,
> -						&hdr);
> +						(struct virtio_net_hdr_v1_hash_tunnel *)&hdr);
>  		if (ret)
>  			return ret;
>  
> -		/*
> -		 * Drop the packet if the configured header size is too small
> -		 * WRT the enabled offloads.
> -		 */
> -		gso = (struct virtio_net_hdr *)&hdr;
> -		ret = __tun_vnet_hdr_put(vnet_hdr_sz, tun->dev->features,
> -					 iter, gso);
> -		if (ret)
> -			return ret;
> +		if (vnet_hdr_sz >= sizeof(struct virtio_net_hdr_v1_hash_tunnel_ts)) {
> +			__le64 tstamp = cpu_to_le64(ktime_get_ns());
> +
> +			hdr.tstamp_0 = (tstamp & 0x000000000000ffffULL) >> 0;
> +			hdr.tstamp_1 = (tstamp & 0x00000000ffff0000ULL) >> 16;
> +			hdr.tstamp_2 = (tstamp & 0x0000ffff00000000ULL) >> 32;
> +			hdr.tstamp_3 = (tstamp & 0xffff000000000000ULL) >> 48;
> +		}
> +
> +		if (unlikely(iov_iter_count(iter) < vnet_hdr_sz))
> +			return -EINVAL;
> +
> +		if (unlikely(copy_to_iter(&hdr, vnet_hdr_sz, iter) != vnet_hdr_sz))
> +			return -EFAULT;
>  	}
>  
>  	if (vlan_hlen) {
> 
> -- 
> 2.52.0
>