// SPDX-License-Identifier: GPL-2.0-only/* * Copyright (c) 2021, Microsoft Corporation. * * Authors: *   Beau Belgrave <beaub@linux.microsoft.com> */ #include <errno.h>#include <sys/ioctl.h>#include <sys/mman.h>#include <fcntl.h>#include <stdio.h>#include <unistd.h>#include <linux/user_events.h> /* Assumes debugfs is mounted */const char *data_file = "/sys/kernel/debug/tracing/user_events_data";const char *status_file = "/sys/kernel/debug/tracing/user_events_status"; static int event_status(char **status){	int fd = open(status_file, O_RDONLY); 	*status = mmap(NULL, sysconf(_SC_PAGESIZE), PROT_READ,		       MAP_SHARED, fd, 0); 	close(fd); 	if (*status == MAP_FAILED)		return -1; 	return 0;} static int event_reg(int fd, const char *command, int *status, int *write){	struct user_reg reg = {0}; 	reg.size = sizeof(reg);	reg.name_args = (__u64)command; 	if (ioctl(fd, DIAG_IOCSREG, &reg) == -1)		return -1; 	*status = reg.status_index;	*write = reg.write_index; 	return 0;} int main(int argc, char **argv){	int data_fd, status, write;	char *status_page;	struct iovec io[2];	__u32 count = 0; 	if (event_status(&status_page) == -1)		return errno; 	data_fd = open(data_file, O_RDWR); 	if (event_reg(data_fd, "test u32 count", &status, &write) == -1)		return errno; 	/* Setup iovec */	io[0].iov_base = &write;	io[0].iov_len = sizeof(write);	io[1].iov_base = &count;	io[1].iov_len = sizeof(count); ask:	printf("Press enter to check status...\n");	getchar(); 	/* Check if anyone is listening */	if (status_page[status]) {		/* Yep, trace out our data */		writev(data_fd, (const struct iovec *)io, 2); 		/* Increase the count */		count++; 		printf("Something was attached, wrote data\n");	} 	goto ask; 	return 0;}