netdev - Re: [PATCH bpf-next v3 11/15] tools/bpf: refactor some net macros to libbpf bpf_tracing

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Date:   Mon, 22 Jun 2020 23:45:56 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Yonghong Song <yhs@...com>
Cc:     bpf <bpf@...r.kernel.org>, Networking <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 v3 11/15] tools/bpf: refactor some net macros to
 libbpf bpf_tracing_net.h

On Mon, Jun 22, 2020 at 5:38 PM Yonghong Song <yhs@...com> wrote:
>
> Refactor bpf_iter_ipv6_route.c and bpf_iter_netlink.c
> so net macros, originally from various include/linux header
> files, are moved to a new libbpf installable header file
> bpf_tracing_net.h. The goal is to improve reuse so
> networking tracing programs do not need to
> copy these macros every time they use them.
>
> Signed-off-by: Yonghong Song <yhs@...com>
> ---
>  tools/lib/bpf/Makefile                           |  1 +
>  tools/lib/bpf/bpf_tracing_net.h                  | 16 ++++++++++++++++
>  .../selftests/bpf/progs/bpf_iter_ipv6_route.c    |  7 +------
>  .../selftests/bpf/progs/bpf_iter_netlink.c       |  4 +---
>  4 files changed, 19 insertions(+), 9 deletions(-)
>  create mode 100644 tools/lib/bpf/bpf_tracing_net.h
>
> diff --git a/tools/lib/bpf/Makefile b/tools/lib/bpf/Makefile
> index bf8ed134cb8a..3d766c80eb78 100644
> --- a/tools/lib/bpf/Makefile
> +++ b/tools/lib/bpf/Makefile
> @@ -257,6 +257,7 @@ install_headers: $(BPF_HELPER_DEFS)
>                 $(call do_install,bpf_helpers.h,$(prefix)/include/bpf,644); \
>                 $(call do_install,$(BPF_HELPER_DEFS),$(prefix)/include/bpf,644); \
>                 $(call do_install,bpf_tracing.h,$(prefix)/include/bpf,644); \
> +               $(call do_install,bpf_tracing_net.h,$(prefix)/include/bpf,644); \
>                 $(call do_install,bpf_endian.h,$(prefix)/include/bpf,644); \
>                 $(call do_install,bpf_core_read.h,$(prefix)/include/bpf,644);
>
> diff --git a/tools/lib/bpf/bpf_tracing_net.h b/tools/lib/bpf/bpf_tracing_net.h
> new file mode 100644
> index 000000000000..1f38a1098727
> --- /dev/null
> +++ b/tools/lib/bpf/bpf_tracing_net.h
> @@ -0,0 +1,16 @@
> +/* SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) */
> +#ifndef __BPF_TRACING_NET_H__
> +#define __BPF_TRACING_NET_H__
> +
> +#define IFNAMSIZ               16
> +
> +#define RTF_GATEWAY            0x0002
> +
> +#define fib_nh_dev             nh_common.nhc_dev
> +#define fib_nh_gw_family       nh_common.nhc_gw_family
> +#define fib_nh_gw6             nh_common.nhc_gw.ipv6
> +
> +#define sk_rmem_alloc          sk_backlog.rmem_alloc
> +#define sk_refcnt              __sk_common.skc_refcnt

Question to networking guys. How probable it is for these and similar
definitions to ever be changed?

I'm a bit hesitant to make any stability guarantees (which is implied
by libbpf-provided headers). I don't want us to get into the game of
trying to maintain this across multiple kernel versions, if they are
going to be changed.

Let's for now keep bpf_tracing_net.h under selftests/bpf? It's still
good to have these definitions, because we can point people to it.

> +
> +#endif

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