netdev - Re: [PATCH v3 bpf-next 5/7] libbpf: move bpf_{helpers,endian,tracing}.h into libbpf

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Date:   Fri, 4 Oct 2019 08:27:58 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     David Ahern <dsahern@...il.com>
Cc:     Andrii Nakryiko <andriin@...com>, bpf <bpf@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Kernel Team <kernel-team@...com>
Subject: Re: [PATCH v3 bpf-next 5/7] libbpf: move bpf_{helpers,endian,tracing}.h
 into libbpf

On Fri, Oct 4, 2019 at 7:47 AM David Ahern <dsahern@...il.com> wrote:
>
> On 10/3/19 3:28 PM, Andrii Nakryiko wrote:
> > Move bpf_helpers.h, bpf_tracing.h, and bpf_endian.h into libbpf. Ensure
> > they are installed along the other libbpf headers. Also, adjust
> > selftests and samples include path to include libbpf now.
>
> There are side effects to bringing bpf_helpers.h into libbpf if this
> gets propagated to the github sync.
>
> bpf_helpers.h references BPF_FUNC_* which are defined in the
> uapi/linux/bpf.h header. That is a kernel version dependent api file
> which means attempts to use newer libbpf with older kernel headers is
> going to throw errors when compiling bpf programs -- bpf_helpers.h will
> contain undefined BPF_FUNC references.

That's true, but I'm wondering if maintaining a copy of that enum in
bpf_helpers.h itself is a good answer here?

bpf_helpers.h will be most probably used with BPF CO-RE and
auto-generated vmlinux.h with all the enums and types. In that case,
you'll probably want to use vmlinux.h for one of the latest kernels
anyways.

Nevertheless, it is a problem and thanks for bringing it up! I'd say
for now we should still go ahead with this move and try to solve with
issue once bpf_helpers.h is in libbpf. If bpf_helpers.h doesn't work
for someone, it's no worse than it is today when users don't have
bpf_helpers.h at all.