netdev - Re: [PATCH v2 2/2] i40e: add support for XDP

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Date:   Thu, 22 Mar 2018 12:58:11 +0100
From:   Jesper Dangaard Brouer <brouer@...hat.com>
To:     Björn Töpel <bjorn.topel@...il.com>
Cc:     brouer@...hat.com, jeffrey.t.kirsher@...el.com,
        intel-wired-lan@...ts.osuosl.org,
        Björn Töpel <bjorn.topel@...el.com>,
        magnus.karlsson@...el.com, netdev@...r.kernel.org,
        alexander.h.duyck@...el.com, alexander.duyck@...il.com
Subject: Re: [PATCH v2 2/2] i40e: add support for XDP_REDIRECT


On Thu, 22 Mar 2018 10:03:07 +0100 Björn Töpel <bjorn.topel@...il.com> wrote:

> +/**
> + * i40e_xdp_xmit - Implements ndo_xdp_xmit
> + * @dev: netdev
> + * @xdp: XDP buffer
> + *
> + * Returns Zero if sent, else an error code
> + **/
> +int i40e_xdp_xmit(struct net_device *dev, struct xdp_buff *xdp)
> +{

The return code is used by the XDP redirect tracepoint... this is the
only way we have to debug/troubleshoot runtime issues with XDP. Thus,
these need to be consistent across drives and distinguishable.

> +	struct i40e_netdev_priv *np = netdev_priv(dev);
> +	unsigned int queue_index = smp_processor_id();
> +	struct i40e_vsi *vsi = np->vsi;
> +	int err;
> +
> +	if (test_bit(__I40E_VSI_DOWN, vsi->state))
> +		return -EINVAL;

Should be: -ENETDOWN

> +
> +	if (!i40e_enabled_xdp_vsi(vsi) || queue_index >= vsi->num_queue_pairs)
> +		return -EINVAL;

Should be: -ENXIO

> +	err = i40e_xmit_xdp_ring(xdp, vsi->xdp_rings[queue_index]);
> +	if (err != I40E_XDP_TX)
> +		return -ENOMEM;

Should be: -ENOSPC

The ENOSPC return code is important, as this can be used as a feedback
to a XDP_REDIRECT load-balancer facility.

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer