Re: [PATCH bpf-next v3 3/4] bpf, bpftool: Generate skeleton for global percpu data

[Leon Hwang <leon.hwang@linux.dev>]

On 28/5/25 06:31, Andrii Nakryiko wrote:
> Adding libbpf-rs maintainer, Daniel, for awareness, as Rust skeleton
> will have to add support for this, once this patch set lands upstream.
> 
> 

[...]

>> +
>> +       if (map_cnt) {
>> +               bpf_object__for_each_map(map, obj) {
>> +                       if (bpf_map__is_internal_percpu(map) &&
>> +                           get_map_ident(map, ident, sizeof(ident)))
>> +                               printf("\tobj->%s = NULL;\n", ident);
>> +               }
>> +       }
> 
> hm... maybe we can avoid this by making libbpf re-mmap() this
> initialization image to be read-only during bpf_object load? Then the
> pointer can stay in the skeleton and be available for querying of
> "initialization values" (if anyone cares), and we won't have any extra
> post-processing steps in code generated skeleton code?
> 
> And Rust skeleton will be able to expose this as a non-mutable
> reference with no extra magic behind it?
> 
> 
We can re-mmap() it as read-only.

However, in the case of the Rust skeleton, users could still use unsafe
code to cast immutable variables to mutable ones.

That said, it's better to guide users toward treating them as immutable.

Thanks,
Leon