signature POSIX_FILESYS =
   sig
      eqtype uid
      eqtype gid
      eqtype file_desc

      val fdToWord: file_desc -> SysWord.word 
      val wordToFD: SysWord.word -> file_desc 

      (* identity functions *)
      val fdToIOD: file_desc -> file_desc (* OS.IO.iodesc *)
      val iodToFD: file_desc (* OS.IO.iodesc *) -> file_desc option
	 
      type dirstream
      val opendir: string -> dirstream
      val readdir: dirstream -> string
      val rewinddir: dirstream -> unit
      val closedir: dirstream -> unit

      val chdir: string -> unit
      val getcwd: unit -> string
	 
      val stdin: file_desc 
      val stdout: file_desc 
      val stderr: file_desc
	 
      structure S :
	 sig
	    type mode
	    include POSIX_FLAGS where type flags = mode 

	    val irwxu: mode 
	    val irusr: mode 
	    val iwusr: mode 
	    val ixusr: mode 
	    val irwxg: mode 
	    val irgrp: mode 
	    val iwgrp: mode 
	    val ixgrp: mode 
	    val irwxo: mode 
	    val iroth: mode 
	    val iwoth: mode 
	    val ixoth: mode 
	    val isuid: mode 
	    val isgid: mode 
	 end

      structure O :
	 sig
	    include POSIX_FLAGS

            val append: flags 
	    val excl: flags 
	    val noctty: flags 
	    val nonblock: flags 
	    val sync: flags 
	    val trunc: flags 
            val text: flags
            val binary: flags
	 end
	 
       datatype open_mode  = O_RDONLY  | O_WRONLY  | O_RDWR

       val openf: string * open_mode * O.flags -> file_desc 
       val createf: string * open_mode * O.flags * S.mode -> file_desc 
       val creat: string * S.mode -> file_desc 
       val umask: S.mode -> S.mode
       val link: {old: string, new: string} -> unit
       val mkdir: string * S.mode -> unit
       val mkfifo: string * S.mode -> unit
       val unlink: string -> unit
       val rmdir: string -> unit
       val rename: {old: string, new: string} -> unit
       val symlink: {old: string, new: string} -> unit
       val readlink: string -> string

       eqtype dev
       val wordToDev: SysWord.word -> dev 
       val devToWord: dev -> SysWord.word 

       eqtype ino
       val wordToIno: SysWord.word -> ino 
       val inoToWord: ino -> SysWord.word 

       structure ST :
	  sig
	     type stat

	     val isDir: stat -> bool 
	     val isChr: stat -> bool 
	     val isBlk: stat -> bool 
	     val isReg: stat -> bool 
	     val isFIFO: stat -> bool 
	     val isLink: stat -> bool 
	     val isSock: stat -> bool 
	     val mode: stat -> S.mode 
	     val ino: stat -> ino 
	     val dev: stat -> dev 
	     val nlink: stat -> int 
	     val uid: stat -> uid 
	     val gid: stat -> gid 
	     val size: stat -> Position.int 
	     val atime: stat -> Time.time 
	     val mtime: stat -> Time.time 
	     val ctime: stat -> Time.time 
	  end

       val stat: string -> ST.stat
       val lstat: string -> ST.stat
       val fstat: file_desc -> ST.stat

       datatype access_mode =
	  A_READ
	| A_WRITE
	| A_EXEC
	  
       val access: string * access_mode list -> bool
       val chmod: string * S.mode -> unit
       val fchmod: file_desc * S.mode -> unit
       val chown: string * uid * gid -> unit
       val fchown: file_desc * uid * gid -> unit
       val utime :
	  string * {actime: Time.time, modtime: Time.time} option -> unit
       val ftruncate: file_desc * Position.int -> unit
       val pathconf: string * string -> SysWord.word option
       val fpathconf: file_desc * string -> SysWord.word option
   end


signature POSIX_FILESYS_EXTRA =
   sig
      include POSIX_FILESYS

      val wordToOpenMode: SysWord.word -> open_mode
   end