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 */ 26 const char *data_file = "/sys/kernel/tracing/user_events_data"; 27 const char *status_file = "/sys/kernel/tracing/user_events_status"; 28 29 static 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 44 static 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 62 int 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 84 ask: 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 } 103