trace/ftrace.c

   1 /*
   2  * Ftrace trace backend
   3  *
   4  * Copyright (C) 2013 Hitachi, Ltd.
   5  * Created by Eiichi Tsukata <eiichi.tsukata.xh@hitachi.com>
   6  *
   7  * This work is licensed under the terms of the GNU GPL, version 2.  See
   8  * the COPYING file in the top-level directory.
   9  *
  10  */
  11
  12 #include "qemu/osdep.h"
  13 #include "trace.h"
  14 #include "trace/control.h"
  15
  16 int trace_marker_fd;
  17
  18 static int find_debugfs(char *debugfs)
  19 {
  20     char type[100];
  21     FILE *fp;
  22
  23     fp = fopen("/proc/mounts", "r");
  24     if (fp == NULL) {
  25         return 0;
  26     }
  27
  28     while (fscanf(fp, "%*s %" STR(PATH_MAX) "s %99s %*s %*d %*d\n",
  29                   debugfs, type) == 2) {
  30         if (strcmp(type, "debugfs") == 0) {
  31             break;
  32         }
  33     }
  34     fclose(fp);
  35
  36     if (strcmp(type, "debugfs") != 0) {
  37         return 0;
  38     }
  39     return 1;
  40 }
  41
  42 bool ftrace_init(void)
  43 {
  44     char debugfs[PATH_MAX];
  45     char path[PATH_MAX];
  46     int debugfs_found;
  47     int trace_fd = -1;
  48
  49     debugfs_found = find_debugfs(debugfs);
  50     if (debugfs_found) {
  51         snprintf(path, PATH_MAX, "%s/tracing/tracing_on", debugfs);
  52         trace_fd = open(path, O_WRONLY);
  53         if (trace_fd < 0) {
  54             if (errno == EACCES) {
  55                 trace_marker_fd = open("/dev/null", O_WRONLY);
  56                 if (trace_marker_fd != -1) {
  57                     return true;
  58                 }
  59             }
  60             perror("Could not open ftrace 'tracing_on' file");
  61             return false;
  62         } else {
  63             if (write(trace_fd, "1", 1) < 0) {
  64                 perror("Could not write to 'tracing_on' file");
  65                 close(trace_fd);
  66                 return false;
  67             }
  68             close(trace_fd);
  69         }
  70         snprintf(path, PATH_MAX, "%s/tracing/trace_marker", debugfs);
  71         trace_marker_fd = open(path, O_WRONLY);
  72         if (trace_marker_fd < 0) {
  73             perror("Could not open ftrace 'trace_marker' file");
  74             return false;
  75         }
  76     } else {
  77         fprintf(stderr, "debugfs is not mounted\n");
  78         return false;
  79     }
  80
  81     return true;
  82 }