Re: [PATCH v2 bpf-next 1/2] libbpf: Allow use of feature cache for non-token cases

[Jiri Olsa <olsajiri@gmail.com>]

On Wed, Apr 08, 2026 at 11:53:23AM +0100, Alan Maguire wrote:
> Allow bpf object feat_cache assignment in BPF selftests
> to simulate missing features via inclusion of libbpf_internal.h
> and use of bpf_object_set_feat_cache() and bpf_object__sanitize_btf() to
> test BTF sanitization for cases where missing features are simulated.
> 
> Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
> ---
>  tools/lib/bpf/libbpf.c          | 12 ++++++++++--
>  tools/lib/bpf/libbpf_internal.h |  3 ++-
>  2 files changed, 12 insertions(+), 3 deletions(-)
> 
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 42bdba4efd0c..b7b636786d38 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -3145,7 +3145,7 @@ static bool btf_needs_sanitization(struct bpf_object *obj)
>  	       !has_layout;
>  }
>  
> -static struct btf *bpf_object__sanitize_btf(struct bpf_object *obj, struct btf *orig_btf)
> +struct btf *bpf_object__sanitize_btf(struct bpf_object *obj, struct btf *orig_btf)
>  {
>  	bool has_func_global = kernel_supports(obj, FEAT_BTF_GLOBAL_FUNC);
>  	bool has_datasec = kernel_supports(obj, FEAT_BTF_DATASEC);
> @@ -5203,12 +5203,20 @@ bool kernel_supports(const struct bpf_object *obj, enum kern_feature_id feat_id)
>  		 */
>  		return true;
>  
> -	if (obj->token_fd)
> +	if (obj->feat_cache)
>  		return feat_supported(obj->feat_cache, feat_id);
>  
>  	return feat_supported(NULL, feat_id);
>  }
>  
> +/* Used in testing to simulate missing features. */
> +void bpf_object_set_feat_cache(struct bpf_object *obj, struct kern_feature_cache *cache)
> +{
> +	if (obj->feat_cache)
> +		zfree(&obj->feat_cache);

nit, no need to zfree, we set it right below

jirka

> +	obj->feat_cache = cache;
> +}
> +
>  static bool map_is_reuse_compat(const struct bpf_map *map, int map_fd)
>  {
>  	struct bpf_map_info map_info;
> diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h
> index cabdaef79098..3781c45b46d3 100644
> --- a/tools/lib/bpf/libbpf_internal.h
> +++ b/tools/lib/bpf/libbpf_internal.h
> @@ -414,6 +414,7 @@ struct kern_feature_cache {
>  
>  bool feat_supported(struct kern_feature_cache *cache, enum kern_feature_id feat_id);
>  bool kernel_supports(const struct bpf_object *obj, enum kern_feature_id feat_id);
> +void bpf_object_set_feat_cache(struct bpf_object *obj, struct kern_feature_cache *cache);
>  
>  int probe_kern_syscall_wrapper(int token_fd);
>  int probe_memcg_account(int token_fd);
> @@ -427,7 +428,7 @@ int libbpf__load_raw_btf(const char *raw_types, size_t types_len,
>  int libbpf__load_raw_btf_hdr(const struct btf_header *hdr,
>  			     const char *raw_types, const char *str_sec,
>  			     const char *layout_sec, int token_fd);
> -
> +struct btf *bpf_object__sanitize_btf(struct bpf_object *obj, struct btf *orig_btf);
>  int btf_load_into_kernel(struct btf *btf,
>  			 char *log_buf, size_t log_sz, __u32 log_level,
>  			 int token_fd);
> -- 
> 2.39.3
>