Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
tjh.dev
kernel
os
linux
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 <fcntl.h>
13#include <stdio.h>
14#include <unistd.h>
15#include <linux/user_events.h>
16
17/* Assumes debugfs is mounted */
18const char *data_file = "/sys/kernel/debug/tracing/user_events_data";
19const char *status_file = "/sys/kernel/debug/tracing/user_events_status";
20
21static int event_status(char **status)
22{
23 int fd = open(status_file, O_RDONLY);
24
25 *status = mmap(NULL, sysconf(_SC_PAGESIZE), PROT_READ,
26 MAP_SHARED, fd, 0);
27
28 close(fd);
29
30 if (*status == MAP_FAILED)
31 return -1;
32
33 return 0;
34}
35
36static int event_reg(int fd, const char *command, int *status, int *write)
37{
38 struct user_reg reg = {0};
39
40 reg.size = sizeof(reg);
41 reg.name_args = (__u64)command;
42
43 if (ioctl(fd, DIAG_IOCSREG, ®) == -1)
44 return -1;
45
46 *status = reg.status_index;
47 *write = reg.write_index;
48
49 return 0;
50}
51
52int main(int argc, char **argv)
53{
54 int data_fd, status, write;
55 char *status_page;
56 struct iovec io[2];
57 __u32 count = 0;
58
59 if (event_status(&status_page) == -1)
60 return errno;
61
62 data_fd = open(data_file, O_RDWR);
63
64 if (event_reg(data_fd, "test u32 count", &status, &write) == -1)
65 return errno;
66
67 /* Setup iovec */
68 io[0].iov_base = &write;
69 io[0].iov_len = sizeof(write);
70 io[1].iov_base = &count;
71 io[1].iov_len = sizeof(count);
72
73ask:
74 printf("Press enter to check status...\n");
75 getchar();
76
77 /* Check if anyone is listening */
78 if (status_page[status]) {
79 /* Yep, trace out our data */
80 writev(data_fd, (const struct iovec *)io, 2);
81
82 /* Increase the count */
83 count++;
84
85 printf("Something was attached, wrote data\n");
86 }
87
88 goto ask;
89
90 return 0;
91}