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 <asm/bitsperlong.h>
16#include <endian.h>
17#include <linux/user_events.h>
18
19#if __BITS_PER_LONG == 64
20#define endian_swap(x) htole64(x)
21#else
22#define endian_swap(x) htole32(x)
23#endif
24
25/* Assumes debugfs is mounted */
26const char *data_file = "/sys/kernel/debug/tracing/user_events_data";
27const char *status_file = "/sys/kernel/debug/tracing/user_events_status";
28
29static int event_status(long **status)
30{
31 int fd = open(status_file, O_RDONLY);
32
33 *status = mmap(NULL, sysconf(_SC_PAGESIZE), PROT_READ,
34 MAP_SHARED, fd, 0);
35
36 close(fd);
37
38 if (*status == MAP_FAILED)
39 return -1;
40
41 return 0;
42}
43
44static int event_reg(int fd, const char *command, long *index, long *mask,
45 int *write)
46{
47 struct user_reg reg = {0};
48
49 reg.size = sizeof(reg);
50 reg.name_args = (__u64)command;
51
52 if (ioctl(fd, DIAG_IOCSREG, ®) == -1)
53 return -1;
54
55 *index = reg.status_bit / __BITS_PER_LONG;
56 *mask = endian_swap(1L << (reg.status_bit % __BITS_PER_LONG));
57 *write = reg.write_index;
58
59 return 0;
60}
61
62int main(int argc, char **argv)
63{
64 int data_fd, write;
65 long index, mask;
66 long *status_page;
67 struct iovec io[2];
68 __u32 count = 0;
69
70 if (event_status(&status_page) == -1)
71 return errno;
72
73 data_fd = open(data_file, O_RDWR);
74
75 if (event_reg(data_fd, "test u32 count", &index, &mask, &write) == -1)
76 return errno;
77
78 /* Setup iovec */
79 io[0].iov_base = &write;
80 io[0].iov_len = sizeof(write);
81 io[1].iov_base = &count;
82 io[1].iov_len = sizeof(count);
83
84ask:
85 printf("Press enter to check status...\n");
86 getchar();
87
88 /* Check if anyone is listening */
89 if (status_page[index] & mask) {
90 /* Yep, trace out our data */
91 writev(data_fd, (const struct iovec *)io, 2);
92
93 /* Increase the count */
94 count++;
95
96 printf("Something was attached, wrote data\n");
97 }
98
99 goto ask;
100
101 return 0;
102}