linux-kernel - Re: [PATCH bpf v2] libbpf: Move BPF_SEQ_PRINTF and BPF_SNPRINTF to bpf

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Date:   Wed, 26 May 2021 10:01:59 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Florent Revest <revest@...omium.org>
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 v2] libbpf: Move BPF_SEQ_PRINTF and BPF_SNPRINTF to bpf_helpers.h

On Wed, May 26, 2021 at 9:36 AM Florent Revest <revest@...omium.org> wrote:
>
> On Wed, May 26, 2021 at 6:34 PM Andrii Nakryiko
> <andrii.nakryiko@...il.com> wrote:
> >
> > On Tue, May 25, 2021 at 1:18 PM Florent Revest <revest@...omium.org> wrote:
> > >
> > > These macros are convenient wrappers around the bpf_seq_printf and
> > > bpf_snprintf helpers. They are currently provided by bpf_tracing.h which
> > > targets low level tracing primitives. bpf_helpers.h is a better fit.
> > >
> > > The __bpf_narg and __bpf_apply macros are needed in both files so
> > > provided twice and guarded by ifndefs.
> > >
> > > Reported-by: Andrii Nakryiko <andrii@...nel.org>
> > > Signed-off-by: Florent Revest <revest@...omium.org>
> > > ---
> > >  kernel/bpf/preload/iterators/iterators.bpf.c  |  1 -
> > >  tools/lib/bpf/bpf_helpers.h                   | 70 +++++++++++++++++++
> > >  tools/lib/bpf/bpf_tracing.h                   | 62 +++-------------
> > >  .../bpf/progs/bpf_iter_bpf_hash_map.c         |  1 -
> > >  .../selftests/bpf/progs/bpf_iter_bpf_map.c    |  1 -
> > >  .../selftests/bpf/progs/bpf_iter_ipv6_route.c |  1 -
> > >  .../selftests/bpf/progs/bpf_iter_netlink.c    |  1 -
> > >  .../selftests/bpf/progs/bpf_iter_task.c       |  1 -
> > >  .../selftests/bpf/progs/bpf_iter_task_btf.c   |  1 -
> > >  .../selftests/bpf/progs/bpf_iter_task_file.c  |  1 -
> > >  .../selftests/bpf/progs/bpf_iter_task_stack.c |  1 -
> > >  .../selftests/bpf/progs/bpf_iter_task_vma.c   |  1 -
> > >  .../selftests/bpf/progs/bpf_iter_tcp4.c       |  1 -
> > >  .../selftests/bpf/progs/bpf_iter_tcp6.c       |  1 -
> > >  .../selftests/bpf/progs/bpf_iter_udp4.c       |  1 -
> > >  .../selftests/bpf/progs/bpf_iter_udp6.c       |  1 -
> > >  .../selftests/bpf/progs/test_snprintf.c       |  1 -
> > >  17 files changed, 80 insertions(+), 67 deletions(-)
> > >
> > > diff --git a/kernel/bpf/preload/iterators/iterators.bpf.c b/kernel/bpf/preload/iterators/iterators.bpf.c
> > > index 52aa7b38e8b8..03af863314ea 100644
> > > --- a/kernel/bpf/preload/iterators/iterators.bpf.c
> > > +++ b/kernel/bpf/preload/iterators/iterators.bpf.c
> > > @@ -2,7 +2,6 @@
> > >  /* Copyright (c) 2020 Facebook */
> > >  #include <linux/bpf.h>
> > >  #include <bpf/bpf_helpers.h>
> > > -#include <bpf/bpf_tracing.h>
> > >  #include <bpf/bpf_core_read.h>
> > >
> > >  #pragma clang attribute push (__attribute__((preserve_access_index)), apply_to = record)
> > > diff --git a/tools/lib/bpf/bpf_helpers.h b/tools/lib/bpf/bpf_helpers.h
> > > index 9720dc0b4605..68d992b30f26 100644
> > > --- a/tools/lib/bpf/bpf_helpers.h
> > > +++ b/tools/lib/bpf/bpf_helpers.h
> > > @@ -158,4 +158,74 @@ enum libbpf_tristate {
> > >  #define __kconfig __attribute__((section(".kconfig")))
> > >  #define __ksym __attribute__((section(".ksyms")))
> > >
> > > +#ifndef ___bpf_concat
> > > +#define ___bpf_concat(a, b) a ## b
> > > +#endif
> > > +#ifndef ___bpf_apply
> > > +#define ___bpf_apply(fn, n) ___bpf_concat(fn, n)
> > > +#endif
> > > +#ifndef ___bpf_nth
> > > +#define ___bpf_nth(_, _1, _2, _3, _4, _5, _6, _7, _8, _9, _a, _b, _c, N, ...) N
> > > +#endif
> > > +#ifndef ___bpf_narg
> > > +#define ___bpf_narg(...) \
> > > +       ___bpf_nth(_, ##__VA_ARGS__, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0)
> > > +#endif
> > > +#ifndef ___bpf_empty
> > > +#define ___bpf_empty(...) \
> > > +       ___bpf_nth(_, ##__VA_ARGS__, N, N, N, N, N, N, N, N, N, N, 0)
> > > +#endif
> >
> > ___bpf_empty doesn't seem to be used, let's remove it for now?
> > Otherwise it looks good.
>
> Yes it's never been used, I thought it was introduced "just in case"
> so I kept it around but then I'll remove it from both bpf_helpers.h
> and bpf_tracing.h

Oh, I didn't realize it's not used in bpf_tracing.h as well. I think
it was used at some point, but probably some subsequent macro
refactorings got rid of it.