netdev - Re: [PATCH v6 01/12] bpf: add XDP prog type for early driver filter

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Date:	Mon, 11 Jul 2016 23:21:48 +0200
From:	Daniel Borkmann <daniel@...earbox.net>
To:	Brenden Blanco <bblanco@...mgrid.com>,
	Tom Herbert <tom@...bertland.com>
CC:	"David S. Miller" <davem@...emloft.net>,
	Linux Kernel Network Developers <netdev@...r.kernel.org>,
	Martin KaFai Lau <kafai@...com>,
	Jesper Dangaard Brouer <brouer@...hat.com>,
	Ari Saha <as754m@....com>,
	Alexei Starovoitov <alexei.starovoitov@...il.com>,
	Or Gerlitz <gerlitz.or@...il.com>,
	john fastabend <john.fastabend@...il.com>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	Thomas Graf <tgraf@...g.ch>
Subject: Re: [PATCH v6 01/12] bpf: add XDP prog type for early driver filter

On 07/11/2016 06:51 PM, Brenden Blanco wrote:
> On Sun, Jul 10, 2016 at 03:56:02PM -0500, Tom Herbert wrote:
>> On Thu, Jul 7, 2016 at 9:15 PM, Brenden Blanco <bblanco@...mgrid.com> wrote:
[...]
>>> +static bool __is_valid_xdp_access(int off, int size,
>>> +                                 enum bpf_access_type type)
>>> +{
>>> +       if (off < 0 || off >= sizeof(struct xdp_md))
>>> +               return false;
>>> +       if (off % size != 0)
>>
>> off & 3 != 0
> Feasible, but was intending to keep with the surrounding style. What do
> the other bpf maintainers think?
>>
>>> +               return false;
>>> +       if (size != 4)
>>> +               return false;
>>
>> If size must always be 4 why is it even an argument?
> Because this is the first time that the verifier has a chance to check
> it, and size == 4 could potentially be a prog_type-specific requirement.

Yep and wrt above, I think it's more important that all is_valid_*_access()
functions are consistent to each other and easily reviewable than adding
optimizations to some of them, which is slow-path anyway. If we find a nice
simplification, then we should apply it also to others obviously.