[PATCH 1/1] net: tun: add XDP metadata support

[Marcus Wichelmann <marcus.wichelmann@xxxxxxxxxxxxxxxx>]

Enable the support for bpf_xdp_adjust_meta for XDP buffers initialized
by the tun driver. This is useful to pass metadata from an XDP program
that's attached to a tap device to following XDP/TC programs.

When used together with vhost_net, the batched XDP buffers were already
initialized with metadata support by the vhost_net driver, but the
metadata was not yet passed to the skb on XDP_PASS. So this also adds
the required skb_metadata_set calls.

Signed-off-by: Marcus Wichelmann <marcus.wichelmann@xxxxxxxxxxxxxxxx>
---
 drivers/net/tun.c | 23 ++++++++++++++++++-----
 1 file changed, 18 insertions(+), 5 deletions(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index e816aaba8..d3cfea40a 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1600,7 +1600,8 @@ static bool tun_can_build_skb(struct tun_struct *tun, struct tun_file *tfile,
 
 static struct sk_buff *__tun_build_skb(struct tun_file *tfile,
 				       struct page_frag *alloc_frag, char *buf,
-				       int buflen, int len, int pad)
+				       int buflen, int len, int pad,
+				       int metasize)
 {
 	struct sk_buff *skb = build_skb(buf, buflen);
 
@@ -1609,6 +1610,8 @@ static struct sk_buff *__tun_build_skb(struct tun_file *tfile,
 
 	skb_reserve(skb, pad);
 	skb_put(skb, len);
+	if (metasize)
+		skb_metadata_set(skb, metasize);
 	skb_set_owner_w(skb, tfile->socket.sk);
 
 	get_page(alloc_frag->page);
@@ -1668,6 +1671,7 @@ static struct sk_buff *tun_build_skb(struct tun_struct *tun,
 	char *buf;
 	size_t copied;
 	int pad = TUN_RX_PAD;
+	int metasize = 0;
 	int err = 0;
 
 	rcu_read_lock();
@@ -1695,7 +1699,7 @@ static struct sk_buff *tun_build_skb(struct tun_struct *tun,
 	if (hdr->gso_type || !xdp_prog) {
 		*skb_xdp = 1;
 		return __tun_build_skb(tfile, alloc_frag, buf, buflen, len,
-				       pad);
+				       pad, metasize);
 	}
 
 	*skb_xdp = 0;
@@ -1709,7 +1713,7 @@ static struct sk_buff *tun_build_skb(struct tun_struct *tun,
 		u32 act;
 
 		xdp_init_buff(&xdp, buflen, &tfile->xdp_rxq);
-		xdp_prepare_buff(&xdp, buf, pad, len, false);
+		xdp_prepare_buff(&xdp, buf, pad, len, true);
 
 		act = bpf_prog_run_xdp(xdp_prog, &xdp);
 		if (act == XDP_REDIRECT || act == XDP_TX) {
@@ -1730,12 +1734,16 @@ static struct sk_buff *tun_build_skb(struct tun_struct *tun,
 
 		pad = xdp.data - xdp.data_hard_start;
 		len = xdp.data_end - xdp.data;
+
+		metasize = xdp.data - xdp.data_meta;
+		metasize = metasize > 0 ? metasize : 0;
 	}
 	bpf_net_ctx_clear(bpf_net_ctx);
 	rcu_read_unlock();
 	local_bh_enable();
 
-	return __tun_build_skb(tfile, alloc_frag, buf, buflen, len, pad);
+	return __tun_build_skb(tfile, alloc_frag, buf, buflen, len, pad,
+			       metasize);
 
 out:
 	bpf_net_ctx_clear(bpf_net_ctx);
@@ -2452,6 +2460,7 @@ static int tun_xdp_one(struct tun_struct *tun,
 	struct sk_buff_head *queue;
 	u32 rxhash = 0, act;
 	int buflen = hdr->buflen;
+	int metasize = 0;
 	int ret = 0;
 	bool skb_xdp = false;
 	struct page *page;
@@ -2467,7 +2476,6 @@ static int tun_xdp_one(struct tun_struct *tun,
 		}
 
 		xdp_init_buff(xdp, buflen, &tfile->xdp_rxq);
-		xdp_set_data_meta_invalid(xdp);
 
 		act = bpf_prog_run_xdp(xdp_prog, xdp);
 		ret = tun_xdp_act(tun, xdp_prog, xdp, act);
@@ -2507,6 +2515,11 @@ 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);
 
+	metasize = xdp->data - xdp->data_meta;
+	metasize = metasize > 0 ? metasize : 0;
+	if (metasize)
+		skb_metadata_set(skb, metasize);
+
 	if (virtio_net_hdr_to_skb(skb, gso, tun_is_little_endian(tun))) {
 		atomic_long_inc(&tun->rx_frame_errors);
 		kfree_skb(skb);
-- 
2.48.1