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(file: data_file, O_RDWR);
46
47 if (event_reg(fd: data_fd, command: "test u32 count", write: &write, enabled: &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(format: "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(fd: data_fd, iovec: (const struct iovec *)io, count: 2);
63
64 /* Increase the count */
65 count++;
66
67 printf(format: "Something was attached, wrote data\n");
68 }
69
70 goto ask;
71
72 return 0;
73}
74

source code of linux/samples/user_events/example.c