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 tracefs_found;
  46     int trace_fd = -1;
  47     const char *subdir = "";
  48
  49     tracefs_found = find_mount(mount_point, "tracefs");
  50     if (!tracefs_found) {
  51         tracefs_found = find_mount(mount_point, "debugfs");
  52         subdir = "/tracing";
  53     }
  54
  55     if (tracefs_found) {
  56         if (snprintf(path, PATH_MAX, "%s%s/tracing_on", mount_point, subdir)
  57                 >= sizeof(path)) {
  58             fprintf(stderr, "Using tracefs mountpoint would exceed PATH_MAX\n");
  59             return false;
  60         }
  61         trace_fd = open(path, O_WRONLY);
  62         if (trace_fd < 0) {
  63             if (errno == EACCES) {
  64                 trace_marker_fd = open("/dev/null", O_WRONLY);
  65                 if (trace_marker_fd != -1) {
  66                     return true;
  67                 }
  68             }
  69             perror("Could not open ftrace 'tracing_on' file");
  70             return false;
  71         } else {
  72             if (write(trace_fd, "1", 1) < 0) {
  73                 perror("Could not write to 'tracing_on' file");
  74                 close(trace_fd);
  75                 return false;
  76             }
  77             close(trace_fd);
  78         }
  79         if (snprintf(path, PATH_MAX, "%s%s/trace_marker", mount_point, subdir)
  80                 >= sizeof(path)) {
  81             fprintf(stderr, "Using tracefs mountpoint would exceed PATH_MAX\n");
  82             return false;
  83         }
  84         trace_marker_fd = open(path, O_WRONLY);
  85         if (trace_marker_fd < 0) {
  86             perror("Could not open ftrace 'trace_marker' file");
  87             return false;
  88         }
  89     } else {
  90         fprintf(stderr, "tracefs is not mounted\n");
  91         return false;
  92     }
  93
  94     return true;
  95 }