linux-kernel - [PATCH v4 1/2] libbpf: Add the ability to suppress perf event enablement

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Message-ID: <20250806114227.14617-2-iii@linux.ibm.com>
Date: Wed,  6 Aug 2025 13:40:34 +0200
From: Ilya Leoshkevich <iii@...ux.ibm.com>
To: Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>, Ian Rogers <irogers@...gle.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>
Cc: bpf@...r.kernel.org, linux-perf-users@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
        Thomas Richter <tmricht@...ux.ibm.com>, Jiri Olsa <jolsa@...nel.org>,
        Heiko Carstens <hca@...ux.ibm.com>, Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Ilya Leoshkevich <iii@...ux.ibm.com>,
        Eduard Zingerman <eddyz87@...il.com>
Subject: [PATCH v4 1/2] 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.

Acked-by: Eduard Zingerman <eddyz87@...il.com>
Suggested-by: Jiri Olsa <jolsa@...nel.org>
Tested-by: Thomas Richter <tmricht@...ux.ibm.com>
Co-developed-by: Thomas Richter <tmricht@...ux.ibm.com>
Signed-off-by: Thomas Richter <tmricht@...ux.ibm.com>
Signed-off-by: Ilya Leoshkevich <iii@...ux.ibm.com>
---
 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..8f5a81b672e1 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, dont_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..455a957cb702 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 dont_enable;
 	size_t :0;
 };
-#define bpf_perf_event_opts__last_field force_ioctl_attach
+#define bpf_perf_event_opts__last_field dont_enable
 
 LIBBPF_API struct bpf_link *
 bpf_program__attach_perf_event(const struct bpf_program *prog, int pfd);
-- 
2.50.1