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 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, ®) == -1) 32 return -1; 33 34 *write = reg.write_index; 35 36 return 0; 37 } 38 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