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

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Date:   Mon, 14 Aug 2017 10:43:54 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Jason Wang <jasowang@...hat.com>
CC:     davem@...emloft.net, mst@...hat.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, kubakici@...pl
Subject: Re: [PATCH net-next V2 3/3] tap: XDP support

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);
>