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/control.h"
  14 #include "trace/ftrace.h"
  15
  16 int trace_marker_fd;
  17
  18 static int find_mount(char *mount_point, const char *fstype)
  19 {
  20     char type[100];
  21     FILE *fp;
  22     int ret = 0;
  23
  24     fp = fopen("/proc/mounts", "r");
  25     if (fp == NULL) {
  26         return 0;
  27     }
  28
  29     while (fscanf(fp, "%*s %" STR(PATH_MAX) "s %99s %*s %*d %*d\n",
  30                   mount_point, type) == 2) {
  31         if (strcmp(type, fstype) == 0) {
  32             ret = 1;
  33             break;
  34         }
  35     }
  36     fclose(fp);
  37
  38     return ret;
  39 }
  40
  41 bool ftrace_init(void)
  42 {
  43     char mount_point[PATH_MAX];
  44     char path[PATH_MAX];
  45     int debugfs_found;
  46     int trace_fd = -1;
  47
  48     debugfs_found = find_mount(mount_point, "debugfs");
  49     if (debugfs_found) {
  50         snprintf(path, PATH_MAX, "%s/tracing/tracing_on", mount_point);
  51         trace_fd = open(path, O_WRONLY);
  52         if (trace_fd < 0) {
  53             if (errno == EACCES) {
  54                 trace_marker_fd = open("/dev/null", O_WRONLY);
  55                 if (trace_marker_fd != -1) {
  56                     return true;
  57                 }
  58             }
  59             perror("Could not open ftrace 'tracing_on' file");
  60             return false;
  61         } else {
  62             if (write(trace_fd, "1", 1) < 0) {
  63                 perror("Could not write to 'tracing_on' file");
  64                 close(trace_fd);
  65                 return false;
  66             }
  67             close(trace_fd);
  68         }
  69         snprintf(path, PATH_MAX, "%s/tracing/trace_marker", mount_point);
  70         trace_marker_fd = open(path, O_WRONLY);
  71         if (trace_marker_fd < 0) {
  72             perror("Could not open ftrace 'trace_marker' file");
  73             return false;
  74         }
  75     } else {
  76         fprintf(stderr, "debugfs is not mounted\n");
  77         return false;
  78     }
  79
  80     return true;
  81 }