Re: [PATCH bpf-next v13 14/14] bpf: pass btf object id in bpf_map_info.

[Martin KaFai Lau <martin.lau@xxxxxxxxx>]

On 12/8/23 4:27 PM, thinker.li@xxxxxxxxx wrote:
> From: Kui-Feng Lee <thinker.li@xxxxxxxxx>
>
> Include btf object id (btf_obj_id) in bpf_map_info so that tools (ex:
> bpftools struct_ops dump) know the correct btf from the kernel to look up
> type information of struct_ops types.
>
> Since struct_ops types can be defined and registered in a module. The
> type information of a struct_ops type are defined in the btf of the
> module defining it.  The userspace tools need to know which btf is for
> the module defining a struct_ops type.
>
> Signed-off-by: Kui-Feng Lee <thinker.li@xxxxxxxxx>
> ---
>   include/linux/bpf.h            | 1 +
>   include/uapi/linux/bpf.h       | 2 +-
>   kernel/bpf/bpf_struct_ops.c    | 7 +++++++
>   kernel/bpf/syscall.c           | 2 ++
>   tools/include/uapi/linux/bpf.h | 2 +-
>   5 files changed, 12 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index c881befa35f5..26103d8a4374 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -3350,5 +3350,6 @@ struct bpf_struct_ops_##_name {					\
>   int bpf_struct_ops_desc_init(struct bpf_struct_ops_desc *st_ops_desc,
>   			     struct btf *btf,
>   			     struct bpf_verifier_log *log);
> +void bpf_map_struct_ops_info_fill(struct bpf_map_info *info, struct bpf_map *map);

This needs to be in the CONFIG_BPF_JIT guard also.

>   
>   #endif /* _LINUX_BPF_H */
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 5c3838a97554..716c6b28764d 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -6534,7 +6534,7 @@ struct bpf_map_info {
>   	__u32 btf_id;
>   	__u32 btf_key_type_id;
>   	__u32 btf_value_type_id;
> -	__u32 :32;	/* alignment pad */
> +	__u32 btf_obj_id;

may be "btf_vmlinux_id" to make it clear it is a kernel btf and should be used 
with map_info->btf_vmlinux_value_type_id.

>   	__u64 map_extra;
>   } __attribute__((aligned(8)));
>   
> diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c
> index fd26716fa0f9..51c0de75aa85 100644
> --- a/kernel/bpf/bpf_struct_ops.c
> +++ b/kernel/bpf/bpf_struct_ops.c
> @@ -979,3 +979,10 @@ int bpf_struct_ops_link_create(union bpf_attr *attr)
>   	kfree(link);
>   	return err;
>   }
> +
> +void bpf_map_struct_ops_info_fill(struct bpf_map_info *info, struct bpf_map *map)
> +{
> +	struct bpf_struct_ops_map *st_map = (struct bpf_struct_ops_map *)map;
> +
> +	info->btf_obj_id = btf_obj_id(st_map->btf);
> +}
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index 4aced7e58904..3cab56cd02ff 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -4715,6 +4715,8 @@ static int bpf_map_get_info_by_fd(struct file *file,
>   		info.btf_value_type_id = map->btf_value_type_id;
>   	}
>   	info.btf_vmlinux_value_type_id = map->btf_vmlinux_value_type_id;
> +	if (map->map_type == BPF_MAP_TYPE_STRUCT_OPS)
> +		bpf_map_struct_ops_info_fill(&info, map);

This patch should be moved earlier in the set instead of after the selftest 
patch 13. May be after patch 5 where st_map->btf is added.

and where is the test for this?

>   
>   	if (bpf_map_is_offloaded(map)) {
>   		err = bpf_map_offload_info_fill(&info, map);
> diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
> index 5c3838a97554..716c6b28764d 100644
> --- a/tools/include/uapi/linux/bpf.h
> +++ b/tools/include/uapi/linux/bpf.h
> @@ -6534,7 +6534,7 @@ struct bpf_map_info {
>   	__u32 btf_id;
>   	__u32 btf_key_type_id;
>   	__u32 btf_value_type_id;
> -	__u32 :32;	/* alignment pad */
> +	__u32 btf_obj_id;
>   	__u64 map_extra;
>   } __attribute__((aligned(8)));
>