Re: [PATCH net-next V2 3/3] tap: XDP support

[Daniel Borkmann]

On 08/11/2017 01:41 PM, Jason Wang wrote:

This patch tries to implement XDP for tun. The implementation was
split into two parts:

[...]

@@ -1402,6 +1521,22 @@ static ssize_t tun_get_user(struct tun_struct *tun, 
struct tun_file *tfile,
        skb_reset_network_header(skb);
        skb_probe_transport_header(skb, 0);

+       if (generic_xdp) {
+               struct bpf_prog *xdp_prog;
+               int ret;
+
+               rcu_read_lock();
+               xdp_prog = rcu_dereference(tun->xdp_prog);

The name generic_xdp is a bit confusing in this context given this
is 'native' XDP, perhaps above if (generic_xdp) should have a comment
explaining semantics for tun and how it relates to actual generic xdp
that sits at dev->xdp_prog, and gets run from netif_rx_ni(). Or just
name the bool xdp_handle_gso with a comment that we let the generic
XDP infrastructure deal with non-linear skbs instead of having to
re-implement the do_xdp_generic() internals, plus a statement that
the actual generic XDP comes a bit later in the path. That would at
least make it more obvious to read, imho.

+               if (xdp_prog) {
+                       ret = do_xdp_generic(xdp_prog, skb);
+                       if (ret != XDP_PASS) {
+                               rcu_read_unlock();
+                               return total_len;
+                       }
+               }
+               rcu_read_unlock();
+       }
+
        rxhash = __skb_get_hash_symmetric(skb);
  #ifndef CONFIG_4KSTACKS
        tun_rx_batched(tun, tfile, skb, more);