netdev - Re: [PATCH net-next v2 2/6] sfc: perform XDP processing on received packets

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Date:   Mon, 28 Oct 2019 17:46:18 +0000
From:   Edward Cree <ecree@...arflare.com>
To:     Charles McLachlan <cmclachlan@...arflare.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>
CC:     <davem@...emloft.net>, <netdev@...r.kernel.org>,
        <linux-net-drivers@...arflare.com>
Subject: Re: [PATCH net-next v2 2/6] sfc: perform XDP processing on received
 packets

On 28/10/2019 17:11, Charles McLachlan wrote:
>>> +		efx_free_rx_buffers(rx_queue, rx_buf, 1);
>>> +		break;
>> You can do a /* Fall through */ to case XDP_DROP.
> but not if I put the trace_xdp_exception in as well. I think we're always going 
> to need two efx_free_rx_buffers calls.

This will probably make people scream, but I have an evil hack to deal with
 situations like this:

	default:
		bpf_warn_invalid_xdp_action(xdp_act);
		if (0) /* Fall further */
			/* Fall through */
	case XDP_ABORTED:
		trace_xdp_exception(netdev, xdp_prog, xdp_act);
		/* Fall through */
	case XDP_DROP:
		efx_free_rx_buffers(rx_queue, rx_buf, 1);
		break;

I wonder if gcc's Wimplicit-fallthrough logic can comprehend that?  Or if
 it'll trigger -Wmisleading-indentation?

-Ed