Subject: [RFC net-next 12/14] tun: add a way to inject tx path packet into Rx path

From: Prashant Bhole <[email-masked]>
Date: Wed, 18 Dec 2019 17:10:48 +0900

In order to support XDP_TX from tx path XDP program, we need a way
to inject tx path packet into RX path. Let's modify the RX path
function tun_xdp_one() for this purpose.

This patch adds a parameter to pass information whether packet has
virtio_net header.

Signed-off-by: Prashant Bhole <[email-masked]>
---
 drivers/net/tun.c | 41 +++++++++++++++++++++++++++++++----------
 1 file changed, 31 insertions(+), 10 deletions(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 1afded9252f5..0701a7a80346 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -2238,6 +2238,13 @@ static u32 tun_do_xdp_tx_generic(struct tun_struct *tun,
 	return act;
 }
 
+static int tun_xdp_one(struct tun_struct *tun,
+		       struct tun_file *tfile,
+		       struct xdp_buff *xdp, int *flush,
+		       struct tun_page *tpage, int has_hdr);
+
+static void tun_put_page(struct tun_page *tpage);
+
 static u32 tun_do_xdp_tx(struct tun_struct *tun, struct tun_file *tfile,
 			 struct xdp_frame *frame)
 {
@@ -2543,23 +2550,36 @@ static void tun_put_page(struct tun_page *tpage)
 static int tun_xdp_one(struct tun_struct *tun,
 		       struct tun_file *tfile,
 		       struct xdp_buff *xdp, int *flush,
-		       struct tun_page *tpage)
+		       struct tun_page *tpage, int has_hdr)
 {
 	unsigned int datasize = xdp->data_end - xdp->data;
-	struct tun_xdp_hdr *hdr = xdp->data_hard_start;
-	struct virtio_net_hdr *gso = &hdr->gso;
+	struct virtio_net_hdr *gso = NULL;
 	struct tun_pcpu_stats *stats;
-	struct bpf_prog *xdp_prog;
 	struct sk_buff *skb = NULL;
-	u32 rxhash = 0, act;
-	int buflen = hdr->buflen;
-	int err = 0;
+	struct bpf_prog *xdp_prog;
+	struct tun_xdp_hdr *hdr;
+	unsigned int headroom;
 	bool skb_xdp = false;
+	u32 rxhash = 0, act;
 	struct page *page;
+	int err = 0;
+	int buflen;
+
+	if (has_hdr) {
+		hdr = xdp->data_hard_start;
+		gso = &hdr->gso;
+		buflen = hdr->buflen;
+	} else {
+		/* came here from tun tx path */
+		xdp->data_hard_start -= sizeof(struct xdp_frame);
+		headroom = xdp->data - xdp->data_hard_start;
+		buflen = datasize + headroom +
+			 SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
+	}
 
 	xdp_prog = rcu_dereference(tun->xdp_prog);
 	if (xdp_prog) {
-		if (gso->gso_type) {
+		if (has_hdr && gso->gso_type) {
 			skb_xdp = true;
 			goto build;
 		}
@@ -2604,7 +2624,8 @@ static int tun_xdp_one(struct tun_struct *tun,
 	skb_reserve(skb, xdp->data - xdp->data_hard_start);
 	skb_put(skb, xdp->data_end - xdp->data);
 
-	if (virtio_net_hdr_to_skb(skb, gso, tun_is_little_endian(tun))) {
+	if (has_hdr &&
+	    virtio_net_hdr_to_skb(skb, gso, tun_is_little_endian(tun))) {
 		this_cpu_inc(tun->pcpu_stats->rx_frame_errors);
 		kfree_skb(skb);
 		err = -EINVAL;
@@ -2668,7 +2689,7 @@ static int tun_sendmsg(struct socket *sock, struct msghdr *m, size_t total_len)
 
 		for (i = 0; i < n; i++) {
 			xdp = &((struct xdp_buff *)ctl->ptr)[i];
-			tun_xdp_one(tun, tfile, xdp, &flush, &tpage);
+			tun_xdp_one(tun, tfile, xdp, &flush, &tpage, true);
 		}
 
 		if (flush)
-- 
2.21.0