netdev - Re: [PATCH bpf-next 03/13] bpf: support readonly buffer in verifier

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Date:   Wed, 15 Jul 2020 10:52:50 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Yonghong Song <yhs@...com>
Cc:     bpf <bpf@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Kernel Team <kernel-team@...com>,
        Martin KaFai Lau <kafai@...com>
Subject: Re: [PATCH bpf-next 03/13] bpf: support readonly buffer in verifier

On Wed, Jul 15, 2020 at 10:48 AM Yonghong Song <yhs@...com> wrote:
>
> > PTR_TO_TP_BUFFER was a quick hack for tiny scratch area.
> > Here I think the verifier should be smart from the start. >
> > The next patch populates bpf_ctx_arg_aux with hardcoded 0 and 1.
> > imo that's too hacky. Helper definitions shouldn't be in business
> > of poking into such verifier internals.
>
> The reason I am using 0/1 so later on I can easily correlate
> which rdonly_buf access size corresponds to key or value. I guess
> I can have a verifier callback to given an ctx argument index to
> get the access size.

I see. Hardcoding key vs value in some way is necessary, of course.
Some #define for that with clear name would be good.
I was pointing out that 0/1 were used beyond that need.