netdev - Re: [PATCH net-next v3 4/4] bpf: Add tests and samples for LWT-BPF

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Date:   Tue, 29 Nov 2016 16:17:51 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Thomas Graf <tgraf@...g.ch>
Cc:     davem@...emloft.net, netdev@...r.kernel.org, daniel@...earbox.net,
        tom@...bertland.com, roopa@...ulusnetworks.com,
        hannes@...essinduktion.org
Subject: Re: [PATCH net-next v3 4/4] bpf: Add tests and samples for LWT-BPF

On Tue, Nov 29, 2016 at 02:21:23PM +0100, Thomas Graf wrote:
> Adds a series of test to verify the functionality of attaching
> BPF programs at LWT hooks.
> 
> Also adds a sample which collects a histogram of packet sizes which
> pass through an LWT hook.
> 
> $ ./lwt_len_hist.sh
> Starting netserver with host 'IN(6)ADDR_ANY' port '12865' and family AF_UNSPEC
> MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 192.168.253.2 () port 0 AF_INET : demo
> Recv   Send    Send
> Socket Socket  Message  Elapsed
> Size   Size    Size     Time     Throughput
> bytes  bytes   bytes    secs.    10^6bits/sec
> 
>  87380  16384  16384    10.00    39857.69

Nice!

> +	ret = bpf_redirect(ifindex, 0);
> +	if (ret < 0) {
> +		printk("bpf_redirect() failed: %d\n", ret);
> +		return BPF_DROP;
> +	}

this 'if' looks a bit weird. You're passing 0 as flags,
so this helper will always succeed.
Other sample code often does 'return bpf_redirect(...)'
due to this reasoning.