Re: [PATCH bpf-next v12 06/10] bpftool: Generate skeleton for global percpu data

> diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c
> index a01d06d22d1a3..a50540ef6521c 100644
> --- a/tools/bpf/bpftool/gen.c
> +++ b/tools/bpf/bpftool/gen.c

[ ... ]

> @@ -254,7 +260,7 @@ static const struct btf_type *find_type_for_map(struct btf *btf, const char *map
>  	return NULL;
>  }
>
> -static bool is_mmapable_map(const struct bpf_map *map, char *buf, size_t sz)
> +static bool is_skel_data(const struct bpf_map *map, char *buf, size_t sz)
>  {
>  	size_t tmp_sz;
>
> @@ -263,13 +269,24 @@ static bool is_mmapable_map(const struct bpf_map *map, char *buf, size_t sz)
>  		return true;
>  	}
>
> -	if (!bpf_map__is_internal(map) || !(bpf_map__map_flags(map) & BPF_F_MMAPABLE))
> +	if (!bpf_map__is_internal(map))
>  		return false;
>
>  	if (!get_map_ident(map, buf, sz))
>  		return false;
>
> -	return true;
> +	if (bpf_map__map_flags(map) & BPF_F_MMAPABLE)
> +		return true;
> +
> +	if (bpf_map__type(map) == BPF_MAP_TYPE_PERCPU_ARRAY)
> +		return bpf_map__btf_value_type_id(map) != 0;
> +
> +	return false;
> +}
> +
> +static bool is_mmapable_map(const struct bpf_map *map, char *buf, size_t sz)
> +{
> +	return is_skel_data(map, buf, sz) && bpf_map__type(map) != BPF_MAP_TYPE_PERCPU_ARRAY;
>  }
>
>  static int codegen_datasecs(struct bpf_object *obj, const char *obj_name)
> @@ -287,7 +304,7 @@ static int codegen_datasecs(struct bpf_object *obj, const char *obj_name)
>
>  	bpf_object__for_each_map(map, obj) {
>  		/* only generate definitions for memory-mapped internal maps */
> -		if (!is_mmapable_map(map, map_ident, sizeof(map_ident)))
> +		if (!is_skel_data(map, map_ident, sizeof(map_ident)))
>  			continue;

The comment here says "only generate definitions for memory-mapped
internal maps," but is_skel_data() now also returns true for
BPF_MAP_TYPE_PERCPU_ARRAY maps. Those percpu maps are never
memory-mapped: map_is_mmapable() in tools/lib/bpf/libbpf.c returns false
for LIBBPF_MAP_PERCPU, which is why this patch had to add mprotect() for
the init buffer rather than relying on shared mmap.

When you removed the identical comment from codegen_maps_skeleton()
(line 988), should this one have been updated to say "skeleton data maps"
or "internal maps exposed as skeleton data" to match what is_skel_data()
actually checks?

The same wording also appears at line 534 in codegen_asserts():

>  	bpf_object__for_each_map(map, obj) {
> -		if (!is_mmapable_map(map, map_ident, sizeof(map_ident)))
> +		if (!is_skel_data(map, map_ident, sizeof(map_ident)))
>  			continue;

where the comment above (line 513) says "Emit type size asserts for all
top-level fields in memory-mapped internal maps." That comment now covers
percpu maps too.

[ ... ]


---
AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md

CI run summary: https://github.com/kernel-patches/bpf/actions/runs/31716447858