netdev - Re: [PATCH bpf-next 2/3] bpf: Add BPF program and map iterators as built-in BPF programs.

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Date:   Wed, 8 Jul 2020 14:55:50 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        "David S. Miller" <davem@...emloft.net>,
        Daniel Borkmann <daniel@...earbox.net>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Kernel Team <kernel-team@...com>
Subject: Re: [PATCH bpf-next 2/3] bpf: Add BPF program and map iterators as
 built-in BPF programs.

On Thu, Jul 2, 2020 at 1:04 PM Alexei Starovoitov
<alexei.starovoitov@...il.com> wrote:
>
> From: Alexei Starovoitov <ast@...nel.org>
>
> The program and map iterators work similar to seq_file-s.
> Once the program is pinned in bpffs it can be read with "cat" tool
> to print human readable output. In this case about BPF programs and maps.
> For example:
> $ cat /sys/fs/bpf/progs
>   id name            pages attached
>    5    dump_bpf_map     1 bpf_iter_bpf_map
>    6   dump_bpf_prog     1 bpf_iter_bpf_prog



> $ cat /sys/fs/bpf/maps
>   id name            pages
>    3 iterator.rodata     2
>
> To avoid kernel build dependency on clang 10 separate bpf skeleton generation
> into manual "make" step and instead check-in generated .skel.h into git.
>
> Signed-off-by: Alexei Starovoitov <ast@...nel.org>
> ---
>  kernel/bpf/preload/iterators/.gitignore       |   2 +
>  kernel/bpf/preload/iterators/Makefile         |  57 +++
>  kernel/bpf/preload/iterators/README           |   4 +
>  kernel/bpf/preload/iterators/iterators.bpf.c  |  81 ++++
>  kernel/bpf/preload/iterators/iterators.skel.h | 359 ++++++++++++++++++
>  5 files changed, 503 insertions(+)
>  create mode 100644 kernel/bpf/preload/iterators/.gitignore
>  create mode 100644 kernel/bpf/preload/iterators/Makefile
>  create mode 100644 kernel/bpf/preload/iterators/README
>  create mode 100644 kernel/bpf/preload/iterators/iterators.bpf.c
>  create mode 100644 kernel/bpf/preload/iterators/iterators.skel.h
>

[...]

> +struct seq_file;
> +struct bpf_iter_meta {
> +       struct seq_file *seq;
> +       __u64 session_id;
> +       __u64 seq_num;
> +} __attribute__((preserve_access_index));
> +
> +struct bpf_map_memory {
> +       __u32 pages;
> +};

forgot __attribute__((preserve_access_index)) here?

> +struct bpf_map {
> +       __u32 id;
> +       struct bpf_map_memory memory;
> +       char name[16];
> +} __attribute__((preserve_access_index));
> +

[...]

> +SEC("iter/bpf_map")
> +int dump_bpf_map(struct bpf_iter__bpf_map *ctx)
> +{
> +       struct seq_file *seq = ctx->meta->seq;
> +       __u64 seq_num = ctx->meta->seq_num;
> +       struct bpf_map *map = ctx->map;
> +
> +       if (!map)
> +               return 0;
> +
> +       if (seq_num == 0)
> +               BPF_SEQ_PRINTF(seq, "  id name            pages\n");
> +
> +       BPF_SEQ_PRINTF(seq, "%4u%16s%6d\n", map->id, map->name, map->memory.pages);

Here and below, please use %-16s for left-aligned strings for map name
and prog name.

> +       return 0;
> +}
> +
> +SEC("iter/bpf_prog")
> +int dump_bpf_prog(struct bpf_iter__bpf_prog *ctx)
> +{
> +       struct seq_file *seq = ctx->meta->seq;
> +       __u64 seq_num = ctx->meta->seq_num;
> +       struct bpf_prog *prog = ctx->prog;
> +       struct bpf_prog_aux *aux;
> +
> +       if (!prog)
> +               return 0;
> +
> +       aux = prog->aux;
> +       if (seq_num == 0)
> +               BPF_SEQ_PRINTF(seq, "  id name            pages attached\n");
> +
> +       BPF_SEQ_PRINTF(seq, "%4u%16s%6d %s %s\n", aux->id, aux->name, prog->pages,
> +                      aux->attach_func_name, aux->linked_prog->aux->name);
> +       return 0;
> +}
> +char LICENSE[] SEC("license") = "GPL";

[...]