Re: [PATCH bpf-next v5 2/6] libbpf: set btf_value_type_id of struct bpf_map for struct_ops.

[Kui-Feng Lee <sinquersw@gmail.com>]

On 2/28/24 09:48, Andrii Nakryiko wrote:
> On Mon, Feb 26, 2024 at 5:04 PM Kui-Feng Lee <thinker.li@gmail.com> wrote:
>>
>> For a struct_ops map, btf_value_type_id is the type ID of it's struct
>> type. This value is required by bpftool to generate skeleton including
>> pointers of shadow types. The code generator gets the type ID from
>> bpf_map__btf_vaule_type_id() in order to get the type information of the
>> struct type of a map.
>>
>> Signed-off-by: Kui-Feng Lee <thinker.li@gmail.com>
>> ---
>>   tools/lib/bpf/libbpf.c | 5 ++++-
>>   1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
>> index ef8fd20f33ca..465b50235a01 100644
>> --- a/tools/lib/bpf/libbpf.c
>> +++ b/tools/lib/bpf/libbpf.c
>> @@ -1229,6 +1229,7 @@ static int init_struct_ops_maps(struct bpf_object *obj, const char *sec_name,
>>                  map->name = strdup(var_name);
>>                  if (!map->name)
>>                          return -ENOMEM;
>> +               map->btf_value_type_id = type_id;
>>
> 
> this part is good
> 
>>                  map->def.type = BPF_MAP_TYPE_STRUCT_OPS;
>>                  map->def.key_size = sizeof(int);
>> @@ -4818,7 +4819,9 @@ static int bpf_object__create_map(struct bpf_object *obj, struct bpf_map *map, b
>>          if (obj->btf && btf__fd(obj->btf) >= 0) {
>>                  create_attr.btf_fd = btf__fd(obj->btf);
>>                  create_attr.btf_key_type_id = map->btf_key_type_id;
>> -               create_attr.btf_value_type_id = map->btf_value_type_id;
>> +               create_attr.btf_value_type_id =
>> +                       def->type != BPF_MAP_TYPE_STRUCT_OPS ?
>> +                       map->btf_value_type_id : 0;
> 
> but here I think it's cleaner to reset create_attr.btf_value_type_id
> to zero a bit lower, see that we have special logic for
> PERF_EVENT_ARRAY, CGROUP_ARRAY and a bunch more maps. Just add a case
> for BPF_MAP_TYPE_STRUCT_OPS that will clear
> create_attr.btf_value_type_id only (keeping btf_fd and
> map->btf_value_Type_id intact)

No problem!

> 
>>          }
>>
>>          if (bpf_map_type__is_map_in_map(def->type)) {
>> --
>> 2.34.1
>>