libbpf: Add the ability to suppress perf event enablement

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 <[email protected]>
Co-developed-by: Thomas Richter <[email protected]>
Signed-off-by: Thomas Richter <[email protected]>
Signed-off-by: Ilya Leoshkevich <[email protected]>
Acked-by: Eduard Zingerman <[email protected]>

Author: iii-i

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;

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;
 	size_t :0;
 };
-#define bpf_perf_event_opts__last_field force_ioctl_attach
+#define bpf_perf_event_opts__last_field no_ioctl_enable
 
 LIBBPF_API struct bpf_link *
 bpf_program__attach_perf_event(const struct bpf_program *prog, int pfd);