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, &reg) == -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}