netdev - Re: [PATCH bpf-next 1/2] bpf: adding support for map in map in libbpf

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Date:   Mon, 19 Nov 2018 17:12:43 -0800
From:   Y Song <ys114321@...il.com>
To:     tehnerd@...nerd.com
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH bpf-next 1/2] bpf: adding support for map in map in libbpf

On Mon, Nov 19, 2018 at 4:13 PM Nikita V. Shirokov <tehnerd@...nerd.com> wrote:
>
> idea is pretty simple. for specified map (pointed by struct bpf_map)
> we would provide descriptor of already loaded map, which is going to be
> used as a prototype for inner map. proposed workflow:
> 1) open bpf's object (bpf_object__open)
> 2) create bpf's map which is going to be used as a prototype
> 3) find (by name) map-in-map which you want to load and update w/
> descriptor of inner map w/ a new helper from this patch
> 4) load bpf program w/ bpf_object__load
>
> inner_map_fd is ignored by any other maps asidef from (hash|array) of
> maps
>
> Signed-off-by: Nikita V. Shirokov <tehnerd@...nerd.com>
> ---
>  tools/lib/bpf/libbpf.c | 7 +++++++
>  tools/lib/bpf/libbpf.h | 2 ++
>  2 files changed, 9 insertions(+)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index a01eb9584e52..a2ee1b1a93b6 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -163,6 +163,7 @@ struct bpf_map {
>         char *name;
>         size_t offset;
>         int map_ifindex;
> +       int inner_map_fd;
>         struct bpf_map_def def;
>         __u32 btf_key_type_id;
>         __u32 btf_value_type_id;
> @@ -1146,6 +1147,7 @@ bpf_object__create_maps(struct bpf_object *obj)
>                 create_attr.btf_fd = 0;
>                 create_attr.btf_key_type_id = 0;
>                 create_attr.btf_value_type_id = 0;
> +               create_attr.inner_map_fd = map->inner_map_fd;
>
>                 if (obj->btf && !bpf_map_find_btf_info(map, obj->btf)) {
>                         create_attr.btf_fd = btf__fd(obj->btf);
> @@ -2562,6 +2564,11 @@ void bpf_map__set_ifindex(struct bpf_map *map, __u32 ifindex)
>         map->map_ifindex = ifindex;
>  }
>
> +void bpf_map__add_inner_map_fd(struct bpf_map *map, const int fd)

Do we need "const" attribute here?

> +{
> +       map->inner_map_fd = fd;
> +}
> +
>  static struct bpf_map *
>  __bpf_map__iter(struct bpf_map *m, struct bpf_object *obj, int i)
>  {
> diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
> index b1686a787102..7cb00cd41789 100644
> --- a/tools/lib/bpf/libbpf.h
> +++ b/tools/lib/bpf/libbpf.h
> @@ -293,6 +293,8 @@ LIBBPF_API void bpf_map__set_ifindex(struct bpf_map *map, __u32 ifindex);
>  LIBBPF_API int bpf_map__pin(struct bpf_map *map, const char *path);
>  LIBBPF_API int bpf_map__unpin(struct bpf_map *map, const char *path);
>
> +LIBBPF_API void bpf_map__add_inner_map_fd(struct bpf_map *map, const int fd);
> +
>  LIBBPF_API long libbpf_get_error(const void *ptr);
>
>  struct bpf_prog_load_attr {
> --
> 2.15.1
>