netdev - Re: eBPF - little-endian load instructions?

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Date:   Tue, 11 Apr 2017 13:15:30 +0200
From:   Johannes Berg <johannes@...solutions.net>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>
Subject: Re: eBPF - little-endian load instructions?


> Are you working with an skb at that point in time in wifi? 

Yes.

> There are
> 3 different ways of accessing skb data, see [1] slide 7 - 10. The BPF
> LD_ABS/IND instructions were carried over from cBPF and are the only
> ones that convert to host endianess. It can be used in eBPF as well,
> but there are more efficient ways like 'direct packet access' or
> helpers such as bpf_skb_load_bytes() that load the raw buffers as-is,
> which is probably what you want if I understand you correctly.

Sounds like, yeah.

> There are instructions to convert endianess, see __bpf_prog_run(),
> the ALU_END_TO_BE, ALU_END_TO_LE labels for details. There's a
> BPF_ENDIAN() macro used in the test suite and other places.

Ok, thanks! :)

So sounds like I don't need anything special - should have a patch to
hook up the wifi stuff soon.

johannes