LXR qemu/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
  16int trace_marker_fd;
  17
  18static 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
  41bool 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}
  96