netdev - Re: [PATCH v9 bpf-next 2/3] libbpf: add support for command BPF_ENABLE

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Message-ID: <CAEf4BzY5G1+Uw9MFw_Lywi+5kA07Z78GoSpMNmH_BB7TzgkJcA@mail.gmail.com>
Date:   Sat, 20 Jun 2020 20:07:01 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Song Liu <songliubraving@...com>
Cc:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Andrii Nakryiko <andriin@...com>, 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>
Subject: Re: [PATCH v9 bpf-next 2/3] libbpf: add support for command BPF_ENABLE_STATS

On Mon, May 4, 2020 at 10:47 AM Song Liu <songliubraving@...com> wrote:
>
>
>
> > On May 2, 2020, at 1:00 PM, Alexei Starovoitov <alexei.starovoitov@...il.com> wrote:
> >
> > On Thu, Apr 30, 2020 at 12:15 AM Song Liu <songliubraving@...com> wrote:
> >>
> >> bpf_enable_stats() is added to enable given stats.
> >>
> >> Signed-off-by: Song Liu <songliubraving@...com>
> > ...
> >> diff --git a/tools/lib/bpf/bpf.h b/tools/lib/bpf/bpf.h
> >> index 335b457b3a25..1901b2777854 100644
> >> --- a/tools/lib/bpf/bpf.h
> >> +++ b/tools/lib/bpf/bpf.h
> >> @@ -231,6 +231,7 @@ LIBBPF_API int bpf_load_btf(void *btf, __u32 btf_size, char *log_buf,
> >> LIBBPF_API int bpf_task_fd_query(int pid, int fd, __u32 flags, char *buf,
> >>                                 __u32 *buf_len, __u32 *prog_id, __u32 *fd_type,
> >>                                 __u64 *probe_offset, __u64 *probe_addr);
> >> +LIBBPF_API int bpf_enable_stats(enum bpf_stats_type type);
> >
> > I see odd warning here while building selftests
> >
> > In file included from runqslower.c:10:
> > .../tools/testing/selftests/bpf/tools/include/bpf/bpf.h:234:38:
> > warning: ‘enum bpf_stats_type’ declared inside parameter list will not
> > be visible outside of this definition or declaration
> >  234 | LIBBPF_API int bpf_enable_stats(enum bpf_stats_type type);
> >
> > Since this warning is printed only when building runqslower
> > and the rest of selftests are fine, I'm guessing
> > it's a makefile issue with order of includes?
> >
> > Andrii, could you please take a look ?
> > Not urgent. Just flagging for visibility.
>
> The following should fix it.
>
> Thanks,
> Song
>
> =========================== 8< ==============================
>
> From 485c28c8e2cbcc22aa8fcda82f8f599411faa755 Mon Sep 17 00:00:00 2001
> From: Song Liu <songliubraving@...com>
> Date: Mon, 4 May 2020 10:36:26 -0700
> Subject: [PATCH bpf-next] runqslower: include proper uapi/bpf.h
>
> runqslower doesn't specify include path for uapi/bpf.h. This causes the
> following warning:
>
> In file included from runqslower.c:10:
> .../tools/testing/selftests/bpf/tools/include/bpf/bpf.h:234:38:
> warning: 'enum bpf_stats_type' declared inside parameter list will not
> be visible outside of this definition or declaration
>   234 | LIBBPF_API int bpf_enable_stats(enum bpf_stats_type type);
>
> Fix this by adding -I tools/includ/uapi to the Makefile.
>
> Reported-by: Alexei Starovoitov <ast@...nel.org>
> Signed-off-by: Song Liu <songliubraving@...com>
> ---
>  tools/bpf/runqslower/Makefile | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/tools/bpf/runqslower/Makefile b/tools/bpf/runqslower/Makefile
> index 8a6f82e56a24..722a29a988cd 100644
> --- a/tools/bpf/runqslower/Makefile
> +++ b/tools/bpf/runqslower/Makefile
> @@ -8,7 +8,8 @@ BPFTOOL ?= $(DEFAULT_BPFTOOL)
>  LIBBPF_SRC := $(abspath ../../lib/bpf)
>  BPFOBJ := $(OUTPUT)/libbpf.a
>  BPF_INCLUDE := $(OUTPUT)
> -INCLUDES := -I$(OUTPUT) -I$(BPF_INCLUDE) -I$(abspath ../../lib)
> +INCLUDES := -I$(OUTPUT) -I$(BPF_INCLUDE) -I$(abspath ../../lib)        \
> +       -I$(abspath ../../include/uapi)
>  CFLAGS := -g -Wall
>
>  # Try to detect best kernel BTF source
> --
> 2.24.1
>

This is a partial work-around just for runqslower, which has a luxury
to access the very latest linux/bpf.h. Any other system that doesn't
have the very latest bpf.h header will get warnings about undefined
`enum bpf_stats_type` definition, even if they don't use
bpf_stats_enable(). I think the proper fix here is to add forward
declaration of this enum in libbpf/bpf.h. I'll send a patch in a few
minutes.