Re: [PATCH bpf-next 4/5] tools/bpftool: add `link detach` subcommand

[Song Liu <songliubraving@fb.com>]

> On Jul 29, 2020, at 4:05 PM, Andrii Nakryiko <andriin@fb.com> wrote:
> 
> Add ability to force-detach BPF link. Also add missing error message, if
> specified link ID is wrong.
> 
> Signed-off-by: Andrii Nakryiko <andriin@fb.com>

Acked-by: Song Liu <songliubraving@fb.com>

With two nitpicks below. 

[...]

> static int link_parse_fd(int *argc, char ***argv)
> {
> +	int fd;
> +
> 	if (is_prefix(**argv, "id")) {
> 		unsigned int id;
> 		char *endptr;
> @@ -35,7 +37,10 @@ static int link_parse_fd(int *argc, char ***argv)
> 		}
> 		NEXT_ARGP();
> 
> -		return bpf_link_get_fd_by_id(id);
> +		fd = bpf_link_get_fd_by_id(id);
> +		if (fd < 0)
> +			p_err("failed to get link with ID %d: %d", id, -errno);

How about we print strerror(errno) to match the rest of link.c?

[...]

> +static int do_detach(int argc, char **argv)
> +{
> +	int err, fd;
> +
> +	if (argc != 2)
> +		return BAD_ARG();
> +
> +	fd = link_parse_fd(&argc, &argv);
> +	if (fd < 0)
> +		return 1;
> +
> +	err = bpf_link_detach(fd);
> +	if (err)
> +		err = -errno;
> +	close(fd);
> +	if (err) {
> +		p_err("failed link detach: %d", err);

And strerror(err) here.