netdev - [RFC PATCH v3 04/17] vsock/virtio: non-linear skb handling for tap

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Date: Mon, 22 May 2023 10:39:37 +0300
From: Arseniy Krasnov <AVKrasnov@...rdevices.ru>
To: Stefan Hajnoczi <stefanha@...hat.com>, Stefano Garzarella
	<sgarzare@...hat.com>, "David S. Miller" <davem@...emloft.net>, Eric Dumazet
	<edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni
	<pabeni@...hat.com>, "Michael S. Tsirkin" <mst@...hat.com>, Jason Wang
	<jasowang@...hat.com>, Bobby Eshleman <bobby.eshleman@...edance.com>
CC: <kvm@...r.kernel.org>, <virtualization@...ts.linux-foundation.org>,
	<netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<kernel@...rdevices.ru>, <oxffffaa@...il.com>, <avkrasnov@...rdevices.ru>,
	Arseniy Krasnov <AVKrasnov@...rdevices.ru>
Subject: [RFC PATCH v3 04/17] vsock/virtio: non-linear skb handling for tap

For tap device new skb is created and data from the current skb is
copied to it. This adds copying data from non-linear skb to new
the skb.

Signed-off-by: Arseniy Krasnov <AVKrasnov@...rdevices.ru>
---
 net/vmw_vsock/virtio_transport_common.c | 31 ++++++++++++++++++++++---
 1 file changed, 28 insertions(+), 3 deletions(-)

diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
index 16effa8d55d2..9854f48a0544 100644
--- a/net/vmw_vsock/virtio_transport_common.c
+++ b/net/vmw_vsock/virtio_transport_common.c
@@ -106,6 +106,27 @@ virtio_transport_alloc_skb(struct virtio_vsock_pkt_info *info,
 	return NULL;
 }
 
+static void virtio_transport_copy_nonlinear_skb(struct sk_buff *skb,
+						void *dst,
+						size_t len)
+{
+	struct iov_iter iov_iter = { 0 };
+	struct iovec iovec;
+	size_t to_copy;
+
+	iovec.iov_base = dst;
+	iovec.iov_len = len;
+
+	iov_iter.iter_type = ITER_IOVEC;
+	iov_iter.__iov = &iovec;
+	iov_iter.nr_segs = 1;
+
+	to_copy = min_t(size_t, len, skb->len);
+
+	skb_copy_datagram_iter(skb, VIRTIO_VSOCK_SKB_CB(skb)->frag_off,
+			       &iov_iter, to_copy);
+}
+
 /* Packet capture */
 static struct sk_buff *virtio_transport_build_skb(void *opaque)
 {
@@ -114,7 +135,6 @@ static struct sk_buff *virtio_transport_build_skb(void *opaque)
 	struct af_vsockmon_hdr *hdr;
 	struct sk_buff *skb;
 	size_t payload_len;
-	void *payload_buf;
 
 	/* A packet could be split to fit the RX buffer, so we can retrieve
 	 * the payload length from the header and the buffer pointer taking
@@ -122,7 +142,6 @@ static struct sk_buff *virtio_transport_build_skb(void *opaque)
 	 */
 	pkt_hdr = virtio_vsock_hdr(pkt);
 	payload_len = pkt->len;
-	payload_buf = pkt->data;
 
 	skb = alloc_skb(sizeof(*hdr) + sizeof(*pkt_hdr) + payload_len,
 			GFP_ATOMIC);
@@ -165,7 +184,13 @@ static struct sk_buff *virtio_transport_build_skb(void *opaque)
 	skb_put_data(skb, pkt_hdr, sizeof(*pkt_hdr));
 
 	if (payload_len) {
-		skb_put_data(skb, payload_buf, payload_len);
+		if (skb_is_nonlinear(pkt)) {
+			void *data = skb_put(skb, payload_len);
+
+			virtio_transport_copy_nonlinear_skb(pkt, data, payload_len);
+		} else {
+			skb_put_data(skb, pkt->data, payload_len);
+		}
 	}
 
 	return skb;
-- 
2.25.1