Re: [PATCH bpf-next v3 3/4] libbpf: pass BPF token from find_prog_btf_id to BPF_BTF_GET_FD_BY_ID

[Yonghong Song <yonghong.song@linux.dev>]

On 3/7/25 1:29 PM, Mykyta Yatsenko wrote:
> From: Mykyta Yatsenko <yatsenko@meta.com>
>
> Pass BPF token from bpf_program__set_attach_target to
> BPF_BTF_GET_FD_BY_ID bpf command.
> When freplace program attaches to target program, it needs to look up
> for BTF of the target, this may require BPF token, if, for example,
> running from user namespace.

LGTM with small nit below.

Acked-by: Yonghong Song <yonghong.song@linux.dev>

>
> Signed-off-by: Mykyta Yatsenko <yatsenko@meta.com>
> ---
>   tools/lib/bpf/bpf.c             |  3 ++-
>   tools/lib/bpf/bpf.h             |  4 +++-
>   tools/lib/bpf/btf.c             | 14 ++++++++++++--
>   tools/lib/bpf/libbpf.c          | 10 +++++-----
>   tools/lib/bpf/libbpf_internal.h |  1 +
>   5 files changed, 23 insertions(+), 9 deletions(-)
>
> diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
> index 359f73ead613..783274172e56 100644
> --- a/tools/lib/bpf/bpf.c
> +++ b/tools/lib/bpf/bpf.c
> @@ -1097,7 +1097,7 @@ int bpf_map_get_fd_by_id(__u32 id)
>   int bpf_btf_get_fd_by_id_opts(__u32 id,
>   			      const struct bpf_get_fd_by_id_opts *opts)
>   {
> -	const size_t attr_sz = offsetofend(union bpf_attr, open_flags);
> +	const size_t attr_sz = offsetofend(union bpf_attr, token_fd);
>   	union bpf_attr attr;
>   	int fd;
>   
> @@ -1107,6 +1107,7 @@ int bpf_btf_get_fd_by_id_opts(__u32 id,
>   	memset(&attr, 0, attr_sz);
>   	attr.btf_id = id;
>   	attr.open_flags = OPTS_GET(opts, open_flags, 0);
> +	attr.token_fd = OPTS_GET(opts, token_fd, 0);
>   
>   	fd = sys_bpf_fd(BPF_BTF_GET_FD_BY_ID, &attr, attr_sz);
>   	return libbpf_err_errno(fd);
> diff --git a/tools/lib/bpf/bpf.h b/tools/lib/bpf/bpf.h
> index 435da95d2058..544215d7137c 100644
> --- a/tools/lib/bpf/bpf.h
> +++ b/tools/lib/bpf/bpf.h
> @@ -487,9 +487,11 @@ LIBBPF_API int bpf_link_get_next_id(__u32 start_id, __u32 *next_id);
>   struct bpf_get_fd_by_id_opts {
>   	size_t sz; /* size of this struct for forward/backward compatibility */
>   	__u32 open_flags; /* permissions requested for the operation on fd */
> +	__u32 token_fd;
>   	size_t :0;
>   };
> -#define bpf_get_fd_by_id_opts__last_field open_flags
> +
> +#define bpf_get_fd_by_id_opts__last_field token_fd
>   
>   LIBBPF_API int bpf_prog_get_fd_by_id(__u32 id);
>   LIBBPF_API int bpf_prog_get_fd_by_id_opts(__u32 id,
> diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
> index eea99c766a20..466336f16134 100644
> --- a/tools/lib/bpf/btf.c
> +++ b/tools/lib/bpf/btf.c
> @@ -1619,12 +1619,17 @@ struct btf *btf_get_from_fd(int btf_fd, struct btf *base_btf)
>   	return btf;
>   }
>   
> -struct btf *btf__load_from_kernel_by_id_split(__u32 id, struct btf *base_btf)
> +struct btf *btf_load_from_kernel(__u32 id, struct btf *base_btf, int token_fd)
>   {
>   	struct btf *btf;
>   	int btf_fd;
> +	LIBBPF_OPTS(bpf_get_fd_by_id_opts, opts);
> +
> +	opts.token_fd = token_fd;
> +	if (token_fd)
> +		opts.open_flags |= BPF_F_TOKEN_FD;

To 'move opts.token_fd = token_fd' under if condition? Something like

	if (token_fd) {
		opts.open_flags |= BPF_F_TOKEN_FD;
		opts.token_fd = token_fd;
	}
?

>   
> -	btf_fd = bpf_btf_get_fd_by_id(id);
> +	btf_fd = bpf_btf_get_fd_by_id_opts(id, &opts);
>   	if (btf_fd < 0)
>   		return libbpf_err_ptr(-errno);
>   
>
[...]