Re: [PATCHv3 bpf-next 3/3] bpftool: Add tracing_multi link info output

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
- [Medium] The kernel does not implement `.fill_link_info` for `tracing_multi` links, preventing `bpftool` from querying the data.
- [Low] The patch references `tracing_multi` in `struct bpf_link_info`, but this member is missing from the UAPI header, leading to a compilation error.
--

commit e1b00f15ceb03dae490ba9269f47251c966b9424
Author: Jiri Olsa <jolsa@kernel.org>
bpftool: Add tracing_multi link info output

This commit adds support to bpftool to show tracing_multi link details
such as attach type, btf_id, address, cookie, and function module.

> diff --git a/tools/bpf/bpftool/link.c b/tools/bpf/bpftool/link.c
> index bdcd717b0348f..eb0ba9d716924 100644
> --- a/tools/bpf/bpftool/link.c
> +++ b/tools/bpf/bpftool/link.c

[ ... ]

> @@ -1114,6 +1226,26 @@ static int do_show_link(int fd)
>  			goto again;
>  		}
>  	}
> +	if (info.type == BPF_LINK_TYPE_TRACING_MULTI && !info.tracing_multi.ids) {

[Severity: Low]
The patch references tracing_multi in struct bpf_link_info here, but looking
at include/uapi/linux/bpf.h, there doesn't seem to be a tracing_multi member
defined in the union. Will this cause a compilation error when building bpftool?

[Severity: Medium]
Additionally, it appears the kernel-side bpf_tracing_multi_link_lops in
kernel/trace/bpf_trace.c does not yet implement a .fill_link_info callback.
Without that callback, will bpf_link_get_info_by_fd() fail to populate the
requested tracing_multi arrays (ids, addrs, cookies) for the tool to display,
even after the UAPI is updated?

> +		count = info.tracing_multi.count;
> +		if (count) {
> +			ids = calloc(count, sizeof(__u32));
> +			addrs = calloc(count, sizeof(__u64));
> +			cookies = calloc(count, sizeof(__u64));
> +			if (!ids) {
> +				p_err("mem alloc failed");
> +				close(fd);
> +				free(cookies);
> +				free(addrs);
> +				free(ids);
> +				return -ENOMEM;
> +			}
> +			info.tracing_multi.ids = ptr_to_u64(ids);
> +			info.tracing_multi.addrs = ptr_to_u64(addrs);
> +			info.tracing_multi.cookies = ptr_to_u64(cookies);
> +			goto again;
> +		}
> +	}

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260629143844.862369-4-jolsa@kernel.org?part=1