On Tue, Aug 5, 2025 at 6:04 AM Ilya Leoshkevich <iii@xxxxxxxxxxxxx> wrote:
>
> Automatically enabling a perf event after attaching a BPF prog to it is
> not always desirable.
>
> Add a new no_ioctl_enable field to struct bpf_perf_event_opts. While
> introducing ioctl_enable instead would be nicer in that it would avoid
> a double negation in the implementation, it would make
> DECLARE_LIBBPF_OPTS() less efficient.
>
> Suggested-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> Co-developed-by: Thomas Richter <tmricht@xxxxxxxxxxxxx>
> Signed-off-by: Thomas Richter <tmricht@xxxxxxxxxxxxx>
> Signed-off-by: Ilya Leoshkevich <iii@xxxxxxxxxxxxx>
> ---
> tools/lib/bpf/libbpf.c | 13 ++++++++-----
> tools/lib/bpf/libbpf.h | 4 +++-
> 2 files changed, 11 insertions(+), 6 deletions(-)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index fb4d92c5c339..414c566c4650 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -10965,11 +10965,14 @@ struct bpf_link *bpf_program__attach_perf_event_opts(const struct bpf_program *p
> }
> link->link.fd = pfd;
> }
> - if (ioctl(pfd, PERF_EVENT_IOC_ENABLE, 0) < 0) {
> - err = -errno;
> - pr_warn("prog '%s': failed to enable perf_event FD %d: %s\n",
> - prog->name, pfd, errstr(err));
> - goto err_out;
> +
> + if (!OPTS_GET(opts, no_ioctl_enable, false)) {
> + if (ioctl(pfd, PERF_EVENT_IOC_ENABLE, 0) < 0) {
> + err = -errno;
> + pr_warn("prog '%s': failed to enable perf_event FD %d: %s\n",
> + prog->name, pfd, errstr(err));
> + goto err_out;
> + }
> }
>
> return &link->link;
> diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
> index d1cf813a057b..2d3cc436cdbf 100644
> --- a/tools/lib/bpf/libbpf.h
> +++ b/tools/lib/bpf/libbpf.h
> @@ -499,9 +499,11 @@ struct bpf_perf_event_opts {
> __u64 bpf_cookie;
> /* don't use BPF link when attach BPF program */
> bool force_ioctl_attach;
> + /* don't automatically enable the event */
> + bool no_ioctl_enable;
The patch logic looks fine, but I feel the knob name is too
implementation oriented.
imo "dont_auto_enable" is more descriptive and easier
to reason about.
Let's wait for Eduard/Andrii reviews. This patch has to go
via bpf trees first while the latter via perf.
