netdev - Re: [net-next 5/9] ice: Add support for AF

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Date:   Wed, 30 Oct 2019 11:50:09 -0700
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Jeff Kirsher <jeffrey.t.kirsher@...el.com>
Cc:     davem@...emloft.net,
        Krzysztof Kazimierczak <krzysztof.kazimierczak@...el.com>,
        netdev@...r.kernel.org, nhorman@...hat.com, sassmann@...hat.com,
        Maciej Fijalkowski <maciej.fijalkowski@...el.com>,
        Tony Nguyen <anthony.l.nguyen@...el.com>,
        Andrew Bowers <andrewx.bowers@...el.com>
Subject: Re: [net-next 5/9] ice: Add support for AF_XDP

On Tue, 29 Oct 2019 20:29:06 -0700, Jeff Kirsher wrote:
> +/**
> + * ice_run_xdp_zc - Executes an XDP program in zero-copy path
> + * @rx_ring: Rx ring
> + * @xdp: xdp_buff used as input to the XDP program
> + *
> + * Returns any of ICE_XDP_{PASS, CONSUMED, TX, REDIR}
> + */
> +static int
> +ice_run_xdp_zc(struct ice_ring *rx_ring, struct xdp_buff *xdp)
> +{
> +	int err, result = ICE_XDP_PASS;
> +	struct bpf_prog *xdp_prog;
> +	struct ice_ring *xdp_ring;
> +	u32 act;
> +
> +	rcu_read_lock();
> +	xdp_prog = READ_ONCE(rx_ring->xdp_prog);
> +	if (!xdp_prog) {
> +		rcu_read_unlock();
> +		return ICE_XDP_PASS;
> +	}
> +
> +	act = bpf_prog_run_xdp(xdp_prog, xdp);
> +	xdp->handle += xdp->data - xdp->data_hard_start;
> +	switch (act) {
> +	case XDP_PASS:
> +		break;
> +	case XDP_TX:
> +		xdp_ring = rx_ring->vsi->xdp_rings[rx_ring->q_index];
> +		result = ice_xmit_xdp_buff(xdp, xdp_ring);
> +		break;

From the quick look at the code it wasn't clear to me how you deal with
XDP_TX on ZC frames. Could you describe the flow of such frames a
little bit? 

> +	case XDP_REDIRECT:
> +		err = xdp_do_redirect(rx_ring->netdev, xdp, xdp_prog);
> +		result = !err ? ICE_XDP_REDIR : ICE_XDP_CONSUMED;
> +		break;
> +	default:
> +		bpf_warn_invalid_xdp_action(act);
> +		/* fallthrough -- not supported action */
> +	case XDP_ABORTED:
> +		trace_xdp_exception(rx_ring->netdev, xdp_prog, act);
> +		/* fallthrough -- handle aborts by dropping frame */
> +	case XDP_DROP:
> +		result = ICE_XDP_CONSUMED;
> +		break;
> +	}
> +
> +	rcu_read_unlock();
> +	return result;
> +}