Re: [PATCH bpf-next v2 2/3] bpf: implement link_query callbacks in map element iterators

[Andrii Nakryiko <andrii.nakryiko@gmail.com>]

On Thu, Aug 20, 2020 at 3:50 PM Yonghong Song <yhs@fb.com> wrote:
>
> For bpf_map_elem and bpf_sk_local_storage bpf iterators,
> additional map_id should be shown for fdinfo and
> userspace query. For example, the following is for
> a bpf_map_elem iterator.
>   $ cat /proc/1753/fdinfo/9
>   pos:    0
>   flags:  02000000
>   mnt_id: 14
>   link_type:      iter
>   link_id:        34
>   prog_tag:       104be6d3fe45e6aa
>   prog_id:        173
>   target_name:    bpf_map_elem
>   map_id:         127
>
> Signed-off-by: Yonghong Song <yhs@fb.com>
> ---
>  include/linux/bpf.h       |  4 ++++
>  kernel/bpf/map_iter.c     | 15 +++++++++++++++
>  net/core/bpf_sk_storage.c |  2 ++
>  3 files changed, 21 insertions(+)
>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 529e9b183eeb..30c144af894a 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -1256,6 +1256,10 @@ int bpf_iter_new_fd(struct bpf_link *link);
>  bool bpf_link_is_iter(struct bpf_link *link);
>  struct bpf_prog *bpf_iter_get_info(struct bpf_iter_meta *meta, bool in_stop);
>  int bpf_iter_run_prog(struct bpf_prog *prog, void *ctx);
> +void bpf_iter_map_show_fdinfo(const struct bpf_iter_aux_info *aux,
> +                             struct seq_file *seq);
> +int bpf_iter_map_fill_link_info(const struct bpf_iter_aux_info *aux,
> +                               struct bpf_link_info *info);
>
>  int bpf_percpu_hash_copy(struct bpf_map *map, void *key, void *value);
>  int bpf_percpu_array_copy(struct bpf_map *map, void *key, void *value);
> diff --git a/kernel/bpf/map_iter.c b/kernel/bpf/map_iter.c
> index af86048e5afd..714e74556aa2 100644
> --- a/kernel/bpf/map_iter.c
> +++ b/kernel/bpf/map_iter.c
> @@ -149,6 +149,19 @@ static void bpf_iter_detach_map(struct bpf_iter_aux_info *aux)
>         bpf_map_put_with_uref(aux->map);
>  }
>
> +void bpf_iter_map_show_fdinfo(const struct bpf_iter_aux_info *aux,
> +                             struct seq_file *seq)
> +{
> +       seq_printf(seq, "map_id:\t\t%u\n", aux->map->id);

nit: I think it's a bad idea to have two tabs here to align everything
visually, might make parsing unnecessarily harder

> +}
> +
> +int bpf_iter_map_fill_link_info(const struct bpf_iter_aux_info *aux,
> +                               struct bpf_link_info *info)
> +{
> +       info->iter.map.map_id = aux->map->id;
> +       return 0;
> +}
> +
>  DEFINE_BPF_ITER_FUNC(bpf_map_elem, struct bpf_iter_meta *meta,
>                      struct bpf_map *map, void *key, void *value)
>
> @@ -156,6 +169,8 @@ static const struct bpf_iter_reg bpf_map_elem_reg_info = {
>         .target                 = "bpf_map_elem",
>         .attach_target          = bpf_iter_attach_map,
>         .detach_target          = bpf_iter_detach_map,
> +       .show_fdinfo            = bpf_iter_map_show_fdinfo,
> +       .fill_link_info         = bpf_iter_map_fill_link_info,
>         .ctx_arg_info_size      = 2,
>         .ctx_arg_info           = {
>                 { offsetof(struct bpf_iter__bpf_map_elem, key),
> diff --git a/net/core/bpf_sk_storage.c b/net/core/bpf_sk_storage.c
> index b988f48153a4..281200dc0a01 100644
> --- a/net/core/bpf_sk_storage.c
> +++ b/net/core/bpf_sk_storage.c
> @@ -1437,6 +1437,8 @@ static struct bpf_iter_reg bpf_sk_storage_map_reg_info = {
>         .target                 = "bpf_sk_storage_map",
>         .attach_target          = bpf_iter_attach_map,
>         .detach_target          = bpf_iter_detach_map,
> +       .show_fdinfo            = bpf_iter_map_show_fdinfo,
> +       .fill_link_info         = bpf_iter_map_fill_link_info,
>         .ctx_arg_info_size      = 2,
>         .ctx_arg_info           = {
>                 { offsetof(struct bpf_iter__bpf_sk_storage_map, sk),
> --
> 2.24.1
>