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

From: Daniel Borkmann
Date: Mon Aug 14 2017 - 04:44:07 EST


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);