[PATCH v2 bpf-next 1/2] bpf: adding support for map in map in libbpf

[Nikita V. Shirokov]

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 <tehn...@tehnerd.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..0e229ab037dc 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, int fd)
+{
+       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..0a0b7e0ed554 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, int fd);
+
 LIBBPF_API long libbpf_get_error(const void *ptr);
 
 struct bpf_prog_load_attr {
-- 
2.15.1