[PATCH v5 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

Signed-off-by: Nikita V. Shirokov <tehn...@tehnerd.com>
Acked-by: Yonghong Song <y...@fb.com>
---
 tools/lib/bpf/libbpf.c | 40 ++++++++++++++++++++++++++++++++++------
 tools/lib/bpf/libbpf.h |  2 ++
 2 files changed, 36 insertions(+), 6 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index cb6565d79603..ba12e070f182 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -167,6 +167,7 @@ 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;
@@ -594,6 +595,14 @@ static int compare_bpf_map(const void *_a, const void *_b)
        return a->offset - b->offset;
 }
 
+static bool bpf_map_type__is_map_in_map(enum bpf_map_type type)
+{
+       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)
 {
@@ -657,13 +666,15 @@ 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.
@@ -1164,6 +1175,9 @@ 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_map_in_map(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);
@@ -2621,6 +2635,20 @@ void bpf_map__set_ifindex(struct bpf_map *map, __u32 
ifindex)
        map->map_ifindex = ifindex;
 }
 
+int bpf_map__set_inner_map_fd(struct bpf_map *map, int fd)
+{
+       if (!bpf_map_type__is_map_in_map(map->def.type)) {
+               pr_warning("error: unsupported map type\n");
+               return -EINVAL;
+       }
+       if (map->inner_map_fd != -1) {
+               pr_warning("error: inner_map_fd already specified\n");
+               return -EINVAL;
+       }
+       map->inner_map_fd = fd;
+       return 0;
+}
+
 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..16158b6b213f 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 int 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