[v4,bpf-next,1/2] bpf: adding support for map in map in libbpf

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

Signed-off-by: Nikita V. Shirokov <tehnerd@tehnerd.com>
Acked-by: Yonghong Song <yhs@fb.com>
---
 tools/lib/bpf/libbpf.c | 33 +++++++++++++++++++++++++++------
 tools/lib/bpf/libbpf.h |  2 ++
 2 files changed, 29 insertions(+), 6 deletions(-)

On Tue, Nov 20, 2018 at 05:33:43PM -0800, Nikita V. Shirokov 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
> 
> Signed-off-by: Nikita V. Shirokov <tehnerd@tehnerd.com>
> Acked-by: Yonghong Song <yhs@fb.com>
> ---
>  tools/lib/bpf/libbpf.c | 33 +++++++++++++++++++++++++++------
>  tools/lib/bpf/libbpf.h |  2 ++
>  2 files changed, 29 insertions(+), 6 deletions(-)
> 
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index a01eb9584e52..0f46e8497ab8 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;
> @@ -585,6 +586,14 @@ static int compare_bpf_map(const void *_a, const void *_b)
>  	return a->offset - b->offset;
>  }
>  
> +static bool bpf_map_type__is_mapinmap(enum bpf_map_type type)

there is already public api bpf_create_map_in_map()
Please use the existing naming convention.

> +{
> +	if (type == BPF_MAP_TYPE_ARRAY_OF_MAPS ||
> +	    type == BPF_MAP_TYPE_HASH_OF_MAPS)
> +		return true;
> +	return false;
> +}
> +
>  static int
>  bpf_object__init_maps(struct bpf_object *obj, int flags)
>  {
> @@ -648,13 +657,15 @@ bpf_object__init_maps(struct bpf_object *obj, int flags)
>  	}
>  	obj->nr_maps = nr_maps;
>  
> -	/*
> -	 * fill all fd with -1 so won't close incorrect
> -	 * fd (fd=0 is stdin) when failure (zclose won't close
> -	 * negative fd)).
> -	 */
> -	for (i = 0; i < nr_maps; i++)
> +	for (i = 0; i < nr_maps; i++) {
> +		/*
> +		 * fill all fd with -1 so won't close incorrect
> +		 * fd (fd=0 is stdin) when failure (zclose won't close
> +		 * negative fd)).
> +		 */
>  		obj->maps[i].fd = -1;
> +		obj->maps[i].inner_map_fd = -1;
> +	}
>  
>  	/*
>  	 * Fill obj->maps using data in "maps" section.
> @@ -1146,6 +1157,9 @@ 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;
> +		if (bpf_map_type__is_mapinmap(def->type) &&
> +		    map->inner_map_fd >= 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 +2576,13 @@ void bpf_map__set_ifindex(struct bpf_map *map, __u32 ifindex)
>  	map->map_ifindex = ifindex;
>  }
>  
> +void bpf_map__set_inner_map_fd(struct bpf_map *map, int fd)
> +{
> +	if (bpf_map_type__is_mapinmap(map->def.type) &&
> +	    map->inner_map_fd == -1)
> +		map->inner_map_fd = fd;

return an error?

> +}
> +
>  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..e2132c8c84ae 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__set_inner_map_fd(struct bpf_map *map, int fd);
> +
>  LIBBPF_API long libbpf_get_error(const void *ptr);
>  
>  struct bpf_prog_load_attr {
> -- 
> 2.15.1
>