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
18 const char *data_file = "/sys/kernel/tracing/user_events_data";
19 int enabled = 0;
20
21 static 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, ®) == -1)
32 return -1;
33
34 *write = reg.write_index;
35
36 return 0;
37 }
38
39 int 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);
55 ask:
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
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