netdev - [patch net-next] net: virtio_net: implement exact header length guest feature

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Date:   Fri, 17 Feb 2023 13:15:47 +0100
From:   Jiri Pirko <jiri@...nulli.us>
To:     netdev@...r.kernel.org
Cc:     davem@...emloft.net, kuba@...nel.org, pabeni@...hat.com,
        edumazet@...gle.com, mst@...hat.com, jasowang@...hat.com,
        virtualization@...ts.linux-foundation.org
Subject: [patch net-next] net: virtio_net: implement exact header length guest feature

From: Jiri Pirko <jiri@...dia.com>

virtio_net_hdr_from_skb() fills up hdr_len to skb_headlen(skb).

Virtio spec introduced a feature VIRTIO_NET_F_GUEST_HDRLEN which when
set implicates that the driver provides the exact size of the header.

The driver already complies to fill the correct value. Introduce the
feature and advertise it.

Signed-off-by: Jiri Pirko <jiri@...dia.com>
---
 drivers/net/virtio_net.c        | 6 ++++--
 include/uapi/linux/virtio_net.h | 1 +
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index fb5e68ed3ec2..e85b03988733 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -62,7 +62,8 @@ static const unsigned long guest_offloads[] = {
 	VIRTIO_NET_F_GUEST_UFO,
 	VIRTIO_NET_F_GUEST_CSUM,
 	VIRTIO_NET_F_GUEST_USO4,
-	VIRTIO_NET_F_GUEST_USO6
+	VIRTIO_NET_F_GUEST_USO6,
+	VIRTIO_NET_F_GUEST_HDRLEN
 };
 
 #define GUEST_OFFLOAD_GRO_HW_MASK ((1ULL << VIRTIO_NET_F_GUEST_TSO4) | \
@@ -4213,7 +4214,8 @@ static struct virtio_device_id id_table[] = {
 	VIRTIO_NET_F_CTRL_MAC_ADDR, \
 	VIRTIO_NET_F_MTU, VIRTIO_NET_F_CTRL_GUEST_OFFLOADS, \
 	VIRTIO_NET_F_SPEED_DUPLEX, VIRTIO_NET_F_STANDBY, \
-	VIRTIO_NET_F_RSS, VIRTIO_NET_F_HASH_REPORT, VIRTIO_NET_F_NOTF_COAL
+	VIRTIO_NET_F_RSS, VIRTIO_NET_F_HASH_REPORT, VIRTIO_NET_F_NOTF_COAL, \
+	VIRTIO_NET_F_GUEST_HDRLEN
 
 static unsigned int features[] = {
 	VIRTNET_FEATURES,
diff --git a/include/uapi/linux/virtio_net.h b/include/uapi/linux/virtio_net.h
index b4062bed186a..12c1c9699935 100644
--- a/include/uapi/linux/virtio_net.h
+++ b/include/uapi/linux/virtio_net.h
@@ -61,6 +61,7 @@
 #define VIRTIO_NET_F_GUEST_USO6	55	/* Guest can handle USOv6 in. */
 #define VIRTIO_NET_F_HOST_USO	56	/* Host can handle USO in. */
 #define VIRTIO_NET_F_HASH_REPORT  57	/* Supports hash report */
+#define VIRTIO_NET_F_GUEST_HDRLEN  59	/* Guest provides the exact hdr_len value. */
 #define VIRTIO_NET_F_RSS	  60	/* Supports RSS RX steering */
 #define VIRTIO_NET_F_RSC_EXT	  61	/* extended coalescing info */
 #define VIRTIO_NET_F_STANDBY	  62	/* Act as standby for another device
-- 
2.39.0