samples/user_events/example.c

   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, &reg) == -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 }