Re: [PATCH v2 bpf-next 12/20] libbpf: Add support for bpf_arena.

[Alexei Starovoitov <alexei.starovoitov@gmail.com>]

On Mon, Feb 12, 2024 at 10:12 AM Eduard Zingerman <eddyz87@gmail.com> wrote:
>
> On Thu, 2024-02-08 at 20:06 -0800, Alexei Starovoitov wrote:
> [...]
>
> > @@ -9830,8 +9861,8 @@ int bpf_map__set_value_size(struct bpf_map *map, __u32 size)
> >               int err;
> >               size_t mmap_old_sz, mmap_new_sz;
> >
> > -             mmap_old_sz = bpf_map_mmap_sz(map->def.value_size, map->def.max_entries);
> > -             mmap_new_sz = bpf_map_mmap_sz(size, map->def.max_entries);
> > +             mmap_old_sz = bpf_map_mmap_sz(map);
> > +             mmap_new_sz = __bpf_map_mmap_sz(size, map->def.max_entries);
> >               err = bpf_map_mmap_resize(map, mmap_old_sz, mmap_new_sz);
> >               if (err) {
> >                       pr_warn("map '%s': failed to resize memory-mapped region: %d\n",
>
> I think that as is bpf_map__set_value_size() won't work for arenas.

It doesn't and doesn't work for ringbuf either.
I guess we can add a filter by map type, but I'm not sure
how big this can of worms (extra checks) will be.
There are probably many libbpf apis that can be misused.
Like bpf_map__set_type()