text: /*
   * mount.c, by rmk
   */
  
  #include <sys/mount.h>
  #include <sys/stat.h>
  #include <fcntl.h>
  #include <errno.h>
  #include <stdio.h>
  #include <stdlib.h>
  #include <string.h>
  #include <unistd.h>
  
  #include <linux/loop.h>
  
  #define ARRAY_SIZE(x)	(sizeof(x) / sizeof(x[0]))
  
  #define DEFAULT_LOOP_DEVICE "/dev/block/loop0"
  #define LOOPDEV_MAXLEN 64
  
  struct mount_opts {
  	const char str[8];
  	unsigned long rwmask;
  	unsigned long rwset;
  	unsigned long rwnoset;
  };
  
  struct extra_opts {
  	char *str;
  	char *end;
  	int used_size;
  	int alloc_size;
  };
  
  /*
   * These options define the function of "mount(2)".
   */
  #define MS_TYPE	(MS_REMOUNT|MS_BIND|MS_MOVE)
  
  
  static const struct mount_opts options[] = {
  	/* name		mask		set		noset		*/
  	{ "async",	MS_SYNCHRONOUS,	0,		MS_SYNCHRONOUS	},
  	{ "atime",	MS_NOATIME,	0,		MS_NOATIME	},
  	{ "bind",	MS_TYPE,	MS_BIND,	0,		},
  	{ "dev",	MS_NODEV,	0,		MS_NODEV	},
  	{ "diratime",	MS_NODIRATIME,	0,		MS_NODIRATIME	},
  	{ "dirsync",	MS_DIRSYNC,	MS_DIRSYNC,	0		},
  	{ "exec",	MS_NOEXEC,	0,		MS_NOEXEC	},
  	{ "move",	MS_TYPE,	MS_MOVE,	0		},
  	{ "recurse",	MS_REC,		MS_REC,		0		},
  	{ "rec",	MS_REC,		MS_REC,		0		},
  	{ "remount",	MS_TYPE,	MS_REMOUNT,	0		},
  	{ "ro",		MS_RDONLY,	MS_RDONLY,	0		},
  	{ "rw",		MS_RDONLY,	0,		MS_RDONLY	},
  	{ "suid",	MS_NOSUID,	0,		MS_NOSUID	},
  	{ "sync",	MS_SYNCHRONOUS,	MS_SYNCHRONOUS,	0		},
  	{ "verbose",	MS_VERBOSE,	MS_VERBOSE,	0		},
  	{ "unbindable",	MS_UNBINDABLE,	MS_UNBINDABLE,	0		},
  	{ "private",	MS_PRIVATE,	MS_PRIVATE,	0		},
  	{ "slave",	MS_SLAVE,	MS_SLAVE,	0		},
  	{ "shared",	MS_SHARED,	MS_SHARED,	0		},
  };
  
  static void add_extra_option(struct extra_opts *extra, char *s)
  {
  	int len = strlen(s);
  	int newlen = extra->used_size + len;
  
  	if (extra->str)
  	       len++;			/* +1 for ',' */
  
  	if (newlen >= extra->alloc_size) {
  		char *new;
  
  		new = realloc(extra->str, newlen + 1);	/* +1 for NUL */
  		if (!new)
  			return;
  
  		extra->str = new;
  		extra->end = extra->str + extra->used_size;
  		extra->alloc_size = newlen;
  	}
  
  	if (extra->used_size) {
  		*extra->end = ',';
  		extra->end++;
  	}
  	strcpy(extra->end, s);
  	extra->used_size += len;
  
  }
  
  static unsigned long
  parse_mount_options(char *arg, unsigned long rwflag, struct extra_opts *extra, int* loop, char *loopdev)
  {
  	char *s;
      
      *loop = 0;
  	while ((s = strsep(&arg, ",")) != NULL) {
  		char *opt = s;
  		unsigned int i;
  		int res, no = s[0] == 'n' && s[1] == 'o';
  
  		if (no)
  			s += 2;
  
          if (strncmp(s, "loop=", 5) == 0) {
              *loop = 1;
              strlcpy(loopdev, s + 5, LOOPDEV_MAXLEN);
              continue;
          }
  
          if (strcmp(s, "loop") == 0) {
              *loop = 1;
              strlcpy(loopdev, DEFAULT_LOOP_DEVICE, LOOPDEV_MAXLEN);
              continue;
          }
  		for (i = 0, res = 1; i < ARRAY_SIZE(options); i++) {
  			res = strcmp(s, options[i].str);
  
  			if (res == 0) {
  				rwflag &= ~options[i].rwmask;
  				if (no)
  					rwflag |= options[i].rwnoset;
  				else
  					rwflag |= options[i].rwset;
  			}
  			if (res <= 0)
  				break;
  		}
  
  		if (res != 0 && s[0])
  			add_extra_option(extra, opt);
  	}
  
  	return rwflag;
  }
  
  static char *progname;
  
  static struct extra_opts extra;
  static unsigned long rwflag;
  
  static int
  do_mount(char *dev, char *dir, char *type, unsigned long rwflag, void *data, int loop,
           char *loopdev)
  {
  	char *s;
  	int error = 0;
  
      if (loop) {
          int file_fd, device_fd;
          int flags;
  
          flags = (rwflag & MS_RDONLY) ? O_RDONLY : O_RDWR;
          
          file_fd = open(dev, flags);
          if (file_fd < 0) {
              perror("open backing file failed");
              return 1;
          }
          device_fd = open(loopdev, flags);
          if (device_fd < 0) {
              perror("open loop device failed");
              close(file_fd);
              return 1;
          }
          if (ioctl(device_fd, LOOP_SET_FD, file_fd) < 0) {
              perror("ioctl LOOP_SET_FD failed");
              close(file_fd);
              close(device_fd);
              return 1;
          }
  
          close(file_fd);
          close(device_fd);
          dev = loopdev;
      }
  
  	while ((s = strsep(&type, ",")) != NULL) {
  retry:
  		if (mount(dev, dir, s, rwflag, data) == -1) {
  			error = errno;
  			/*
  			 * If the filesystem is not found, or the
  			 * superblock is invalid, try the next.
  			 */
  			if (error == ENODEV || error == EINVAL)
  				continue;
  
  			/*
  			 * If we get EACCESS, and we're trying to
  			 * mount readwrite and this isn't a remount,
  			 * try read only.
  			 */
  			if (error == EACCES &&
  			    (rwflag & (MS_REMOUNT|MS_RDONLY)) == 0) {
  				rwflag |= MS_RDONLY;
  				goto retry;
  			}
  			break;
  		}
  	}
  
  	if (error) {
  		errno = error;
  		perror("mount");
  		return 255;
  	}
  
  	return 0;
  }
  
  static int print_mounts()
  {
      FILE* f;
      int length;
      char buffer[100];
      
      f = fopen("/proc/mounts", "r");
      if (!f) {
          fprintf(stdout, "could not open /proc/mounts\n");
          return -1;
      }
  
      do {
          length = fread(buffer, 1, 100, f);
          if (length > 0)
              fwrite(buffer, 1, length, stdout);
      } while (length > 0);
  
      fclose(f);
      return 0;
  }
  
  static int get_mounts_dev_dir(const char *arg, char **dev, char **dir)
  {
  	FILE *f;
  	char mount_dev[256];
  	char mount_dir[256];
  	char mount_type[256];
  	char mount_opts[256];
  	int mount_freq;
  	int mount_passno;
  	int match;
  
  	f = fopen("/proc/mounts", "r");
  	if (!f) {
  		fprintf(stdout, "could not open /proc/mounts\n");
  		return -1;
  	}
  
  	do {
  		match = fscanf(f, "%255s %255s %255s %255s %d %d\n",
  					   mount_dev, mount_dir, mount_type,
  					   mount_opts, &mount_freq, &mount_passno);
  		mount_dev[255] = 0;
  		mount_dir[255] = 0;
  		mount_type[255] = 0;
  		mount_opts[255] = 0;
  		if (match == 6 &&
  			(strcmp(arg, mount_dev) == 0 ||
  			 strcmp(arg, mount_dir) == 0)) {
  			*dev = strdup(mount_dev);
  			*dir = strdup(mount_dir);
  			fclose(f);
  			return 0;
  		}
  	} while (match != EOF);
  
  	fclose(f);
  	return -1;
  }
  
  int mount_main(int argc, char *argv[])
  {
  	char *type = NULL;
  	char *dev = NULL;
  	char *dir = NULL;
  	int c;
  	int loop = 0;
  	char loopdev[LOOPDEV_MAXLEN];
  
  	progname = argv[0];
  	rwflag = MS_VERBOSE;
  	
  	// mount with no arguments is equivalent to "cat /proc/mounts"
  	if (argc == 1) return print_mounts();
  
  	do {
  		c = getopt(argc, argv, "o:rt:w");
  		if (c == EOF)
  			break;
  		switch (c) {
  		case 'o':
  			rwflag = parse_mount_options(optarg, rwflag, &extra, &loop, loopdev);
  			break;
  		case 'r':
  			rwflag |= MS_RDONLY;
  			break;
  		case 't':
  			type = optarg;
  			break;
  		case 'w':
  			rwflag &= ~MS_RDONLY;
  			break;
  		case '?':
  			fprintf(stderr, "%s: invalid option -%c\n",
  				progname, optopt);
  			exit(1);
  		}
  	} while (1);
  
  	/*
  	 * If remount, bind or move was specified, then we don't
  	 * have a "type" as such.  Use the dummy "none" type.
  	 */
  	if (rwflag & MS_TYPE)
  		type = "none";
  
  	if (optind + 2 == argc) {
  		dev = argv[optind];
  		dir = argv[optind + 1];
  	} else if (optind + 1 == argc && rwflag & MS_REMOUNT) {
  		get_mounts_dev_dir(argv[optind], &dev, &dir);
  	}
  
  	if (dev == NULL || dir == NULL || type == NULL) {
  		fprintf(stderr, "Usage: %s [-r] [-w] [-o options] [-t type] "
  			"device directory\n", progname);
  		exit(1);
  	}
  
  	return do_mount(dev, dir, type, rwflag, extra.str, loop, loopdev);
  	/* We leak dev and dir in some cases, but we're about to exit */
  }
  