xref: /openbmc/linux/samples/user_events/example.c (revision 9211ddaa)
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 
event_reg(int fd,const char * command,int * write,int * enabled)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, &reg) == -1)
32 		return -1;
33 
34 	*write = reg.write_index;
35 
36 	return 0;
37 }
38 
main(int argc,char ** argv)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