1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * Copyright (c) 2021, Microsoft Corporation.
4 *
5 * Authors:
6 *   Beau Belgrave <beaub@linux.microsoft.com>
7 */
8
9#include <errno.h>
10#include <sys/ioctl.h>
11#include <sys/mman.h>
12#include <sys/uio.h>
13#include <fcntl.h>
14#include <stdio.h>
15#include <unistd.h>
16#include <linux/user_events.h>
17
18const char *data_file = "/sys/kernel/tracing/user_events_data";
19int enabled = 0;
20
21static int event_reg(int fd, const char *command, int *write, int *enabled)
22{
23	struct user_reg reg = {0};
24
25	reg.size = sizeof(reg);
26	reg.enable_bit = 31;
27	reg.enable_size = sizeof(*enabled);
28	reg.enable_addr = (__u64)enabled;
29	reg.name_args = (__u64)command;
30
31	if (ioctl(fd, DIAG_IOCSREG, &reg) == -1)
32		return -1;
33
34	*write = reg.write_index;
35
36	return 0;
37}
38
39int main(int argc, char **argv)
40{
41	int data_fd, write;
42	struct iovec io[2];
43	__u32 count = 0;
44
45	data_fd = open(data_file, O_RDWR);
46
47	if (event_reg(data_fd, "test u32 count", &write, &enabled) == -1)
48		return errno;
49
50	/* Setup iovec */
51	io[0].iov_base = &write;
52	io[0].iov_len = sizeof(write);
53	io[1].iov_base = &count;
54	io[1].iov_len = sizeof(count);
55ask:
56	printf("Press enter to check status...\n");
57	getchar();
58
59	/* Check if anyone is listening */
60	if (enabled) {
61		/* Yep, trace out our data */
62		writev(data_fd, (const struct iovec *)io, 2);
63
64		/* Increase the count */
65		count++;
66
67		printf("Something was attached, wrote data\n");
68	}
69
70	goto ask;
71
72	return 0;
73}
74