libbpf-tools: add CO-RE 'syncsnoop'

This is a CO-RE port of the Brendan Gregg's syncsnoop BCC Python tool.
The code is heavily inspired by the 'runqslower' port, with variables
naming and comments style borrowed from other CO-RE tools.

libbpf-tools/.gitignore

@@ -53,6 +53,7 @@
 /softirqs
 /solisten
 /statsnoop
+/syncsnoop
 /syscount
 /tcpconnect
 /tcpconnlat

libbpf-tools/Makefile

@@ -80,6 +80,7 @@ APPS = \
 	softirqs \
 	solisten \
 	statsnoop \
+	syncsnoop \
 	syscount \
 	tcptracer \
 	tcpconnect \

libbpf-tools/syncsnoop.bpf.c

@@ -0,0 +1,22 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (c) 2024 Tiago Ilieve
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include "syncsnoop.h"
+
+struct {
+	__uint(type, BPF_MAP_TYPE_PERF_EVENT_ARRAY);
+	__uint(key_size, sizeof(u32));
+	__uint(value_size, sizeof(u32));
+} events SEC(".maps");
+
+SEC("tracepoint/syscalls/sys_enter_sync")
+void tracepoint__syscalls__sys_enter_sync(struct trace_event_raw_sys_enter *ctx)
+{
+	struct event event = {};
+
+	event.ts_us = bpf_ktime_get_ns() / 1000;
+	bpf_perf_event_output(ctx, &events, BPF_F_CURRENT_CPU, &event, sizeof(event));
+}
+
+char LICENSE[] SEC("license") = "GPL";

libbpf-tools/syncsnoop.c

@@ -0,0 +1,146 @@
+// SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)
+// Copyright (c) 2024 Tiago Ilieve
+//
+// Based on syncsnoop(8) from BCC by Brendan Gregg.
+// 08-Feb-2024   Tiago Ilieve   Created this.
+#include <argp.h>
+#include <signal.h>
+#include <stdio.h>
+#include <bpf/libbpf.h>
+#include "syncsnoop.h"
+#include "syncsnoop.skel.h"
+
+#define PERF_BUFFER_PAGES       16
+#define PERF_POLL_TIMEOUT_MS    100
+
+static volatile sig_atomic_t exiting = 0;
+
+struct env {
+	bool verbose;
+} env = {};
+
+const char *argp_program_version = "syncsnoop 0.1";
+const char *argp_program_bug_address =
+	"https://github.com/iovisor/bcc/tree/master/libbpf-tools";
+const char argp_program_doc[] =
+"Trace sync syscalls.\n"
+"\n"
+"USAGE: syncsnoop [--help]\n"
+"\n"
+"EXAMPLES:\n"
+"    syncsnoop  # trace sync syscalls\n";
+
+static const struct argp_option opts[] = {
+	{ "verbose", 'v', NULL, 0, "Verbose debug output" },
+	{ NULL, 'h', NULL, OPTION_HIDDEN, "Show the full help" },
+	{},
+};
+
+static error_t parse_arg(int key, char *arg, struct argp_state *state)
+{
+	switch (key) {
+	case 'v':
+		env.verbose = true;
+		break;
+	case 'h':
+		argp_state_help(state, stderr, ARGP_HELP_STD_HELP);
+		break;
+	default:
+		return ARGP_ERR_UNKNOWN;
+	}
+	return 0;
+}
+
+static int libbpf_print_fn(enum libbpf_print_level level, const char *format, va_list args)
+{
+	if (level == LIBBPF_DEBUG && !env.verbose)
+		return 0;
+	return vfprintf(stderr, format, args);
+}
+
+void handle_event(void *ctx, int cpu, void *data, __u32 data_sz)
+{
+	struct event e;
+
+	if (data_sz < sizeof(e)) {
+		printf("Error: packet too small\n");
+		return;
+	}
+	/* Copy data as alignment in the perf buffer isn't guaranteed. */
+	memcpy(&e, data, sizeof(e));
+
+	printf("%-18.9f sync()\n", (float) e.ts_us  / 1000000);
+}
+
+void handle_lost_events(void *ctx, int cpu, __u64 lost_cnt)
+{
+	printf("Lost %llu events on CPU #%d!\n", lost_cnt, cpu);
+}
+
+static void sig_int(int signo)
+{
+	exiting = 1;
+}
+
+int main(int argc, char **argv)
+{
+	static const struct argp argp = {
+		.options = opts,
+		.parser = parse_arg,
+		.doc = argp_program_doc,
+	};
+	struct perf_buffer *pb = NULL;
+	struct syncsnoop_bpf *obj;
+	int err;
+
+	err = argp_parse(&argp, argc, argv, 0, NULL, NULL);
+	if (err)
+		return err;
+
+	libbpf_set_print(libbpf_print_fn);
+
+	obj = syncsnoop_bpf__open_and_load();
+	if (!obj) {
+		fprintf(stderr, "failed to open and load BPF object\n");
+		return 1;
+	}
+
+	err = syncsnoop_bpf__attach(obj);
+	if (err) {
+		fprintf(stderr, "failed to attach BPF object\n");
+		return 1;
+	}
+
+	pb = perf_buffer__new(bpf_map__fd(obj->maps.events), PERF_BUFFER_PAGES,
+			      handle_event, handle_lost_events, NULL, NULL);
+	if (!pb) {
+		err = -errno;
+		fprintf(stderr, "failed to open perf buffer: %d\n", err);
+		goto cleanup;
+	}
+
+	if (signal(SIGINT, sig_int) == SIG_ERR) {
+		fprintf(stderr, "can't set signal handler: %s\n", strerror(errno));
+		err = 1;
+		goto cleanup;
+	}
+
+	/* print header */
+	printf("%-18s %s\n", "TIME(s)", "CALL");
+
+	while (!exiting) {
+		err = perf_buffer__poll(pb, PERF_POLL_TIMEOUT_MS);
+		if (err < 0 && err != -EINTR) {
+			fprintf(stderr, "error polling perf buffer: %s\n", strerror(-err));
+			goto cleanup;
+		}
+		/* reset err to return 0 if exiting */
+		err = 0;
+	}
+
+cleanup:
+	perf_buffer__free(pb);
+	syncsnoop_bpf__destroy(obj);
+
+	return err != 0;
+}

libbpf-tools/syncsnoop.h

@@ -0,0 +1,9 @@
+/* SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) */
+#ifndef __SYNCSNOOP_H
+#define __SYNCSNOOP_H
+
+struct event {
+	__u64 ts_us;
+};
+
+#endif /* __SYNCSNOOP_H */

man/man8/syncsnoop.8

@@ -48,6 +48,7 @@ Linux
 .SH STABILITY
 Unstable - in development.
 .SH AUTHOR
-Brendan Gregg
+Brendan Gregg, original BCC Python version
+Tiago Ilieve, CO-RE version
 .SH SEE ALSO
 iostat(1)