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

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Message-Id: <20191028.110556.665626038293022035.davem@davemloft.net>
Date:   Mon, 28 Oct 2019 11:05:56 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     ecree@...arflare.com
Cc:     cmclachlan@...arflare.com, brouer@...hat.com,
        netdev@...r.kernel.org, linux-net-drivers@...arflare.com
Subject: Re: [PATCH net-next v2 2/6] sfc: perform XDP processing on
 received packets

From: Edward Cree <ecree@...arflare.com>
Date: Mon, 28 Oct 2019 17:46:18 +0000

> 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?

I would seriously prefer a goto to this...