On Tue, 22 Oct 2019 16:38:27 +0100
Charles McLachlan [off-list ref] wrote:

+/** efx_do_xdp: perform XDP processing on a received packet
+ *
+ * Returns true if packet should still be delivered.
+ */
+static bool efx_do_xdp(struct efx_nic *efx, struct efx_channel *channel,
+		       struct efx_rx_buffer *rx_buf, u8 **ehp)
+{
+	u8 rx_prefix[EFX_MAX_RX_PREFIX_SIZE];
+	struct efx_rx_queue *rx_queue;
+	struct bpf_prog *xdp_prog;
+	struct xdp_buff xdp;
+	u32 xdp_act;
+	s16 offset;
+	int rc;
+
+	rcu_read_lock();
+	xdp_prog = rcu_dereference(efx->xdp_prog);
+	if (!xdp_prog) {
+		rcu_read_unlock();
+		return true;
+	}
+
+	rx_queue = efx_channel_get_rx_queue(channel);
+
+	if (unlikely(channel->rx_pkt_n_frags > 1)) {
+		/* We can't do XDP on fragmented packets - drop. */
+		rcu_read_unlock();
+		efx_free_rx_buffers(rx_queue, rx_buf,
+				    channel->rx_pkt_n_frags);
+		if (net_ratelimit())
+			netif_err(efx, rx_err, efx->net_dev,
+				  "XDP is not possible with multiple receive fragments (%d)\n",
+				  channel->rx_pkt_n_frags);
+		return false;
+	}
+
+	dma_sync_single_for_cpu(&efx->pci_dev->dev, rx_buf->dma_addr,
+				rx_buf->len, DMA_FROM_DEVICE);
+
+	/* Save the rx prefix. */
+	EFX_WARN_ON_PARANOID(efx->rx_prefix_size > EFX_MAX_RX_PREFIX_SIZE);
+	memcpy(rx_prefix, *ehp - efx->rx_prefix_size,
+	       efx->rx_prefix_size);
+
+	xdp.data = *ehp;
+	xdp.data_hard_start = xdp.data - XDP_PACKET_HEADROOM;
+
+	/* No support yet for XDP metadata */
+	xdp_set_data_meta_invalid(&xdp);
+	xdp.data_end = xdp.data + rx_buf->len;
+	xdp.rxq = &rx_queue->xdp_rxq_info;
+
+	xdp_act = bpf_prog_run_xdp(xdp_prog, &xdp);
+	rcu_read_unlock();
+
+	offset = (u8 *)xdp.data - *ehp;
+
+	switch (xdp_act) {
+	case XDP_PASS:
+		/* Fix up rx prefix. */
+		if (offset) {
+			*ehp += offset;
+			rx_buf->page_offset += offset;
+			rx_buf->len -= offset;
+			memcpy(*ehp - efx->rx_prefix_size, rx_prefix,
+			       efx->rx_prefix_size);
+		}
+		break;
+
+	case XDP_TX:
+		return -EOPNOTSUPP;
+
+	case XDP_REDIRECT:
+		rc = xdp_do_redirect(efx->net_dev, &xdp, xdp_prog);
+		if (rc) {

Can we call the 'rc' variable 'err' instead?
And give it an unlikely().

+			efx_free_rx_buffers(rx_queue, rx_buf, 1);
+			if (net_ratelimit())
+				netif_err(efx, rx_err, efx->net_dev,
+					  "XDP redirect failed (%d)\n", rc);
+		}
+		break;
+
+	default:
+		bpf_warn_invalid_xdp_action(xdp_act);
+		/* Fall through */
+	case XDP_ABORTED:
+		efx_free_rx_buffers(rx_queue, rx_buf, 1);
+		break;
+
+	case XDP_DROP:
+		efx_free_rx_buffers(rx_queue, rx_buf, 1);
+		break;
+	}
+
+	return xdp_act == XDP_PASS;
+}
+

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