Re: [PATCH bpf-next v3] libbpf: Fix expected_attach_type set when kernel not support

[Jiri Olsa <olsajiri@gmail.com>]

On Sat, Sep 14, 2024 at 11:40:40PM +0800, Tao Chen wrote:
> The commit "5902da6d8a52" set expected_attach_type again with
> field of bpf_program after libpf_prepare_prog_load, which makes
> expected_attach_type = 0 no sense when kenrel not support the
> attach_type feature, so fix it.
> 
> Fixes: 5902da6d8a52 ("libbpf: Add uprobe multi link support to bpf_program__attach_usdt")
> Suggested-by: Jiri Olsa <jolsa@kernel.org>
> Signed-off-by: Tao Chen <chen.dylane@gmail.com>
> ---
>  tools/lib/bpf/libbpf.c | 12 ++++++++----
>  1 file changed, 8 insertions(+), 4 deletions(-)
> 
> Change list:
> - v2 -> v3:
>     - update BPF_TRACE_UPROBE_MULTI both in prog and opts suggedted by
>       Andrri
> - v1 -> v2:
>     - restore the original initialization way suggested by Jiri
> 
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 219facd0e66e..a78e24ff354b 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -7352,8 +7352,14 @@ static int libbpf_prepare_prog_load(struct bpf_program *prog,
>  		opts->prog_flags |= BPF_F_XDP_HAS_FRAGS;
>  
>  	/* special check for usdt to use uprobe_multi link */
> -	if ((def & SEC_USDT) && kernel_supports(prog->obj, FEAT_UPROBE_MULTI_LINK))
> +	if ((def & SEC_USDT) && kernel_supports(prog->obj, FEAT_UPROBE_MULTI_LINK)) {
> +		/* for BPF_TRACE_KPROBE_MULTI, user might want to query exected_attach_type
> +		 * in prog, and expected_attach_type we set in kenrel is from opts, so we
> +		 * update both.
> +		 */

s/K/U/ in BPF_TRACE_KPROBE_MULTI in above comment and 'kenrel' typo

Acked-by: Jiri Olsa <jolsa@kernel.org>

thanks,
jirka

>  		prog->expected_attach_type = BPF_TRACE_UPROBE_MULTI;
> +		opts->expected_attach_type = BPF_TRACE_UPROBE_MULTI;
> +	}
>  
>  	if ((def & SEC_ATTACH_BTF) && !prog->attach_btf_id) {
>  		int btf_obj_fd = 0, btf_type_id = 0, err;
> @@ -7443,6 +7449,7 @@ static int bpf_object_load_prog(struct bpf_object *obj, struct bpf_program *prog
>  	load_attr.attach_btf_id = prog->attach_btf_id;
>  	load_attr.kern_version = kern_version;
>  	load_attr.prog_ifindex = prog->prog_ifindex;
> +	load_attr.expected_attach_type = prog->expected_attach_type;
>  
>  	/* specify func_info/line_info only if kernel supports them */
>  	if (obj->btf && btf__fd(obj->btf) >= 0 && kernel_supports(obj, FEAT_BTF_FUNC)) {
> @@ -7474,9 +7481,6 @@ static int bpf_object_load_prog(struct bpf_object *obj, struct bpf_program *prog
>  		insns_cnt = prog->insns_cnt;
>  	}
>  
> -	/* allow prog_prepare_load_fn to change expected_attach_type */
> -	load_attr.expected_attach_type = prog->expected_attach_type;
> -
>  	if (obj->gen_loader) {
>  		bpf_gen__prog_load(obj->gen_loader, prog->type, prog->name,
>  				   license, insns, insns_cnt, &load_attr,
> -- 
> 2.25.1
>