[RFC net-next 09/18] tun: add a way to inject Tx path packet into Rx path

[Prashant Bhole]

In order to support XDP_TX from offloaded 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. When header isn't present, it is considered as
XDP_TX'ed packet from offloaded program.

Signed-off-by: Prashant Bhole <prashantbhole.li...@gmail.com>
---
 drivers/net/tun.c | 35 ++++++++++++++++++++++++++++-------
 1 file changed, 28 insertions(+), 7 deletions(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 466ea69f00ee..8d6cdd3e5139 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -2221,6 +2221,13 @@ static u32 tun_do_xdp_offload_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_offload(struct tun_struct *tun, struct tun_file *tfile,
                              struct xdp_frame *frame)
 {
@@ -2527,23 +2534,36 @@ 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 tun_xdp_hdr *hdr;
+       struct virtio_net_hdr *gso;
        struct tun_pcpu_stats *stats;
        struct bpf_prog *xdp_prog;
        struct sk_buff *skb = NULL;
+       unsigned int headroom;
        u32 rxhash = 0, act;
-       int buflen = hdr->buflen;
+       int buflen;
        int err = 0;
        bool skb_xdp = false;
        struct page *page;
 
+       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;
                }
@@ -2588,7 +2608,8 @@ 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;
@@ -2652,7 +2673,7 @@ 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)
-- 
2.20.1