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

On Thu, Aug 13, 2026 at 8:24 AM Leon Hwang <[email protected]> wrote:
>
> Enhance bpftool to generate skeletons that properly handle global percpu
> variables. The generated skeleton now includes a dedicated structure for
> percpu data, allowing users to initialize and access percpu variables more
> efficiently.
>
> For global percpu variables, the skeleton now includes a nested
> structure, e.g.:
>
> struct test_global_percpu_data {
>         struct bpf_object_skeleton *skeleton;
>         struct bpf_object *obj;
>         struct {
>                 struct bpf_map *percpu;
>         } maps;
>         // ...
>         struct test_global_percpu_data__percpu {
>                 int data;
>                 char run;
>                 struct {
>                         char set;
>                         int i;
>                         int nums[7];
>                 } struct_data;
>                 int nums[7];
>         } *percpu;
>
>         // ...
> };
>
>   * The "struct test_global_percpu_data__percpu *percpu" points to
>     initialized data, which is actually "maps.percpu->mmaped".
>   * Before loading the skeleton, updating the
>     "struct test_global_percpu_data__percpu *percpu" modifies the initial
>     value of the corresponding global percpu variables.
>   * After loading the skeleton, "maps.percpu->mmaped" has been marked as
>     read-only in libbpf. If users want to update the global percpu
>     variables, they have to update the "maps.percpu" map instead.
>   * For lightweight skeleton, "lskel->percpu" will be protected by
>     "mprotect(p, sz, PROT_READ)".
>   * For subskeleton, those variables of global percpu data will be
>     skipped.
>
> Acked-by: Quentin Monnet <[email protected]>
> Assisted-by: Codex:gpt-5.5-xhigh
> Signed-off-by: Leon Hwang <[email protected]>
> ---
>  tools/bpf/bpftool/gen.c       | 53 +++++++++++++++++++++++++++--------
>  tools/lib/bpf/skel_internal.h | 24 ++++++++++++++--
>  2 files changed, 63 insertions(+), 14 deletions(-)

[...]

> @@ -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;

why do we need this btf_value_type_id() check? in what case it's
expected that there will be no BTF info set?

> +
> +       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;
>  }
>

[...]