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

["Nikita V. Shirokov" <tehnerd@tehnerd.com>]

On Mon, Nov 19, 2018 at 05:12:43PM -0800, Y Song wrote:
> On Mon, Nov 19, 2018 at 4:13 PM Nikita V. Shirokov <tehnerd@tehnerd.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@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..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?
>

i can drop it in v2
 
> > +{
> > +       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
> >