linux-kernel - [PATCH RFC v2 1/2] tun: support rx-tstamp

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Message-Id: <20260129-v6-7-topic-virtio-net-ptp-v2-1-30a27dc52760@pengutronix.de>
Date: Thu, 29 Jan 2026 09:06:41 +0100
From: Steffen Trumtrar <s.trumtrar@...gutronix.de>
To: "Michael S. Tsirkin" <mst@...hat.com>, Jason Wang <jasowang@...hat.com>, 
 Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, 
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
 Richard Cochran <richardcochran@...il.com>, 
 Willem de Bruijn <willemdebruijn.kernel@...il.com>, 
 Andrew Lunn <andrew+netdev@...n.ch>, 
 Eugenio Pérez <eperezma@...hat.com>
Cc: virtualization@...ts.linux.dev, netdev@...r.kernel.org, 
 linux-kernel@...r.kernel.org, Steffen Trumtrar <s.trumtrar@...gutronix.de>
Subject: [PATCH RFC v2 1/2] tun: support rx-tstamp

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 <s.trumtrar@...gutronix.de>
---
 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;
+
+		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