linux-kernel - Re: [PATCH bpf] libbpf: Move BPF_SEQ_PRINTF and BPF_SNPRINTF to bpf

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Date:   Tue, 25 May 2021 22:04:12 +0200
From:   Florent Revest <revest@...omium.org>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     bpf <bpf@...r.kernel.org>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        KP Singh <kpsingh@...nel.org>,
        Brendan Jackman <jackmanb@...gle.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH bpf] libbpf: Move BPF_SEQ_PRINTF and BPF_SNPRINTF to bpf_helpers.h

On Tue, May 25, 2021 at 9:51 PM Andrii Nakryiko
<andrii.nakryiko@...il.com> wrote:
>
> On Tue, May 25, 2021 at 4:38 AM Florent Revest <revest@...omium.org> wrote:
> > +#define ___bpf_concat(a, b) a ## b
> > +#define ___bpf_apply(fn, n) ___bpf_concat(fn, n)
> > +#define ___bpf_nth(_, _1, _2, _3, _4, _5, _6, _7, _8, _9, _a, _b, _c, N, ...) N
> > +#define ___bpf_narg(...) \
> > +       ___bpf_nth(_, ##__VA_ARGS__, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0)
>
> wouldn't this conflict if both bpf_tracing.h and bpf_helpers.h are
> included in the same file?

Oh, yeah, somehow I thought that double macro definitions wouldn't
generate warnings but it would, indeed. Silly me :)

> We can probably guard this block with
> custom #ifdef both in bpf_helpers.h and bpf_tracing.h to avoid
> dependency on order of includes?

Indeed, I think the cleanest would be:
#ifndef ___bpf_concat
#define ___bpf_concat(a, b) a ## b
#endif
#ifndef ___bpf_apply
 etc...

I'm sending a v2.