// 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 <sys/uio.h> #include <fcntl.h> #include <stdio.h> #include <unistd.h> #include <linux/user_events.h> const char *data_file = "/sys/kernel/tracing/user_events_data"; int enabled = 0; static int event_reg(int fd, const char *command, int *write, int *enabled) { struct user_reg reg = {0}; reg.size = sizeof(reg); reg.enable_bit = 31; reg.enable_size = sizeof(*enabled); reg.enable_addr = (__u64)enabled; reg.name_args = (__u64)command; if (ioctl(fd, DIAG_IOCSREG, ®) == -1) return -1; *write = reg.write_index; return 0; } int main(int argc, char **argv) { int data_fd, write; struct iovec io[2]; __u32 count = 0; data_fd = open(data_file, O_RDWR); if (event_reg(data_fd, "test u32 count", &write, &enabled) == -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 (enabled) { /* 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; }