#include <errno.h>
  #include <stdio.h>
  #include <stdlib.h>
  #include <string.h>
  #include <stdbool.h>
  #include <sys/vfs.h>

  #include <sys/mount.h>

  #include <linux/kernel.h>
  
  #include "debugfs.h"

  char debugfs_mountpoint[PATH_MAX + 1] = "/sys/kernel/debug";

  static const char * const debugfs_known_mountpoints[] = {

  	"/sys/kernel/debug",
  	"/debug",

  	0,
  };

  static bool debugfs_found;

  
  /* find the path to the mounted debugfs */
  const char *debugfs_find_mountpoint(void)
  {

  	const char * const *ptr;

  	char type[100];
  	FILE *fp;
  
  	if (debugfs_found)

  		return (const char *)debugfs_mountpoint;

  
  	ptr = debugfs_known_mountpoints;
  	while (*ptr) {
  		if (debugfs_valid_mountpoint(*ptr) == 0) {

  			debugfs_found = true;

  			strcpy(debugfs_mountpoint, *ptr);
  			return debugfs_mountpoint;
  		}
  		ptr++;
  	}
  
  	/* give up and parse /proc/mounts */
  	fp = fopen("/proc/mounts", "r");
  	if (fp == NULL)

  		return NULL;

  	while (fscanf(fp, "%*s %" STR(PATH_MAX) "s %99s %*s %*d %*d
  ",

  		      debugfs_mountpoint, type) == 2) {
  		if (strcmp(type, "debugfs") == 0)
  			break;
  	}
  	fclose(fp);
  
  	if (strcmp(type, "debugfs") != 0)
  		return NULL;

  	debugfs_found = true;

  
  	return debugfs_mountpoint;
  }
  
  /* verify that a mountpoint is actually a debugfs instance */
  
  int debugfs_valid_mountpoint(const char *debugfs)
  {
  	struct statfs st_fs;
  
  	if (statfs(debugfs, &st_fs) < 0)
  		return -ENOENT;

  	else if ((long)st_fs.f_type != (long)DEBUGFS_MAGIC)

  		return -ENOENT;
  
  	return 0;
  }

  /* mount the debugfs somewhere if it's not mounted */

  char *debugfs_mount(const char *mountpoint)

  {

  	/* see if it's already mounted */

  	if (debugfs_find_mountpoint())

  		goto out;

  
  	/* if not mounted and no argument */
  	if (mountpoint == NULL) {
  		/* see if environment variable set */
  		mountpoint = getenv(PERF_DEBUGFS_ENVIRONMENT);
  		/* if no environment variable, use default */
  		if (mountpoint == NULL)
  			mountpoint = "/sys/kernel/debug";
  	}

  	if (mount(NULL, mountpoint, "debugfs", 0, NULL) < 0)
  		return NULL;

  	/* save the mountpoint */

  	debugfs_found = true;

  	strncpy(debugfs_mountpoint, mountpoint, sizeof(debugfs_mountpoint));
  out:

  	return debugfs_mountpoint;

  }