netdev - Re: more test

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Message-Id: <20170426.105511.742633353102583622.davem@davemloft.net>
Date:   Wed, 26 Apr 2017 10:55:11 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     daniel@...earbox.net
Cc:     ast@...com, netdev@...r.kernel.org
Subject: Re: more test_progs...

From: Daniel Borkmann <daniel@...earbox.net>
Date: Wed, 26 Apr 2017 10:14:42 +0200

> On 04/26/2017 05:42 AM, Alexei Starovoitov wrote:
>> That sucks for sparc, of course. I don't have good suggestions for
>> workaround other than marking tcphdr as packed :(
>>  From code efficiency point of view it still will be faster than
>> LD_ABS insn.
> 
> Plus, ld_abs would also only work on skbs right now, and would
> need JIT support for XDP. But it's also cumbersome to use with
> f.e. IPv6, etc, so should not be encouraged, imo.
> 
> One other option for !HAVE_EFFICIENT_UNALIGNED_ACCESS archs could
> be to provide a bpf_skb_load_bytes() helper equivalent for XDP,
> where you eventually do the memcpy() inside. We could see to inline
> the helper itself to optimize it slightly.

We have to do something that works transparently and always,
regardless of whether HAVE_EFFICIENT_UNALIGNED_ACCESS is in
play or not.

And no, marking objects with __packed is not the answer.

What's happening right now is completely unacceptable.