netdev - Re: [PATCH RFC v4 bpf-next 08/11] tun: Support xdp in the Tx path for skb

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Date:   Tue, 3 Mar 2020 08:36:01 -0700
From:   David Ahern <dahern@...italocean.com>
To:     Jesper Dangaard Brouer <brouer@...hat.com>,
        David Ahern <dsahern@...nel.org>
Cc:     netdev@...r.kernel.org, davem@...emloft.net, kuba@...nel.org,
        prashantbhole.linux@...il.com, jasowang@...hat.com,
        toke@...hat.com, mst@...hat.com, toshiaki.makita1@...il.com,
        daniel@...earbox.net, john.fastabend@...il.com, ast@...nel.org,
        kafai@...com, songliubraving@...com, yhs@...com, andriin@...com,
        dsahern@...il.com
Subject: Re: [PATCH RFC v4 bpf-next 08/11] tun: Support xdp in the Tx path for
 skb

On 3/3/20 3:46 AM, Jesper Dangaard Brouer wrote:
> On Wed, 26 Feb 2020 20:20:10 -0700
> David Ahern <dsahern@...nel.org> wrote:
> 
>> +static u32 tun_do_xdp_tx_generic(struct tun_struct *tun,
>> +				 struct net_device *dev,
>> +				 struct sk_buff *skb)
>> +{
>> +	struct bpf_prog *xdp_prog;
>> +	u32 act = XDP_PASS;
>> +
>> +	xdp_prog = rcu_dereference(tun->xdp_egress_prog);
>> +	if (xdp_prog) {
>> +		struct xdp_txq_info txq = { .dev = dev };
>> +		struct xdp_buff xdp;
>> +
>> +		skb = tun_prepare_xdp_skb(skb);
>> +		if (!skb) {
>> +			act = XDP_DROP;
>> +			goto out;
>> +		}
>> +
>> +		xdp.txq = &txq;
>> +
>> +		act = do_xdp_generic_core(skb, &xdp, xdp_prog);
>> +		switch (act) {
>> +		case XDP_TX:    /* for Tx path, XDP_TX == XDP_PASS */
>> +			act = XDP_PASS;
>> +			break;
>> +		case XDP_PASS:
>> +			break;
>> +		case XDP_REDIRECT:
>> +			/* fall through */
>> +		default:
>> +			bpf_warn_invalid_xdp_action(act);
>> +			/* fall through */
>> +		case XDP_ABORTED:
>> +			trace_xdp_exception(tun->dev, xdp_prog, act);
> 
> Hmm, don't we need to extend the trace_xdp_exception() to give users a
> hint that this happened on the TX/egress path?

tracepoint has the program id, unsupported action and device. Seems like
the program id is sufficient. I do need to update libbpf to account for
the attach type.