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

[Tao Chen <chen.dylane@gmail.com>]

在 2024/9/14 23:40, Tao Chen 写道:
> 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.
> +		 */
>   		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,

Hi, guys, please review this patch again, the previous versions:
v1:
https://lore.kernel.org/bpf/20240913121627.153898-1-chen.dylane@gmail.com/
v2:
https://lore.kernel.org/bpf/20240913164355.176021-1-chen.dylane@gmail.com/

-- 
Best Regards
Dylane Chen