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

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Date:   Wed, 30 Nov 2016 07:52:05 +0100
From:   Thomas Graf <tgraf@...g.ch>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
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 11/29/16 at 04:17pm, Alexei Starovoitov wrote:
> 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.

Right, the if branch is absolutely useless. I will remove it.