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	(multiple-value-bind
	    (posn errno)
	    (unix:unix-lseek (fd-stream-fd stream) 0 unix:l_incr)
	  (declare (type (or index null) posn))
	  (cond ((fixnump posn)
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		 ;; Adjust for buffered output:
		 ;;  If there is any output buffered, the *real* file position
		 ;; will be larger than reported by lseek because lseek
		 ;; obviously cannot take into account output we have not
		 ;; sent yet.
		 (dolist (later (fd-stream-output-later stream))
		   (incf posn (- (the index (caddr later))
				 (the index (cadr later)))))
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		 (incf posn (fd-stream-obuf-tail stream))
		 ;; Adjust for unread input:
		 ;;  If there is any input read from UNIX but not supplied to
		 ;; the user of the stream, the *real* file position will
		 ;; smaller than reported, because we want to look like the
		 ;; unread stuff is still available.
		 (decf posn (- (fd-stream-ibuf-tail stream)
			       (fd-stream-ibuf-head stream)))
		 (when (fd-stream-unread stream)
		   (decf posn))
		 ;; Divide bytes by element size.
		 (truncate posn (fd-stream-element-size stream)))
		((eq errno unix:espipe)
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		 nil)
		(t
		 (system:with-interrupts
		   (error "Error lseek'ing ~S: ~A"
			  stream
			  (unix:get-unix-error-msg errno)))))))
      (let ((offset 0) origin)
	(declare (type index offset))
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	;; Make sure we don't have any output pending, because if we move the
	;; file pointer before writing this stuff, it will be written in the
	;; wrong location.
	(flush-output-buffer stream)
	(do ()
	    ((null (fd-stream-output-later stream)))
	  (system:serve-all-events))
	;; Clear out any pending input to force the next read to go to the
	;; disk.
	(setf (fd-stream-unread stream) nil)
	(setf (fd-stream-ibuf-head stream) 0)
	(setf (fd-stream-ibuf-tail stream) 0)
	;; Trash cashed value for listen, so that we check next time.
	(setf (fd-stream-listen stream) nil)
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	(cond ((eq newpos :start)
	       (setf offset 0 origin unix:l_set))
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	      ((eq newpos :end)
	       (setf offset 0 origin unix:l_xtnd))
	      ((typep newpos 'index)
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	       (setf offset (* newpos (fd-stream-element-size stream))
		     origin unix:l_set))
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	      (t
	       (error "Invalid position given to file-position: ~S" newpos)))
	(multiple-value-bind
	    (posn errno)
	    (unix:unix-lseek (fd-stream-fd stream) offset origin)
	  (cond ((typep posn 'fixnum)
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		 t)
		((eq errno unix:espipe)
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		 nil)
		(t
		 (error "Error lseek'ing ~S: ~A"
			stream
			(unix:get-unix-error-msg errno))))))))
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;;;; Creation routines (MAKE-FD-STREAM and OPEN)

;;; MAKE-FD-STREAM -- Public.
;;;
;;; Returns a FD-STREAM on the given file.
;;;
(defun make-fd-stream (fd
		       &key
		       (input nil input-p)
		       (output nil output-p)
		       (element-type 'base-char)
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		       (buffering :full)
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		       file
		       original
		       delete-original
		       input-buffer-p
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		       (name (if file
				 (format nil "file ~S" file)
				 (format nil "descriptor ~D" fd)))
		       auto-close)
  (declare (type index fd) (type (or index null) timeout)
	   (type (member :none :line :full) buffering))
  "Create a stream for the given unix file descriptor.
  If input is non-nil, allow input operations.
  If output is non-nil, allow output operations.
  If neither input nor output are specified, default to allowing input.
  Element-type indicates the element type to use (as for open).
  Buffering indicates the kind of buffering to use.
  Timeout (if true) is the number of seconds to wait for input.  If NIL (the
    default), then wait forever.  When we time out, we signal IO-TIMEOUT.
  File is the name of the file (will be returned by PATHNAME).
  Name is used to identify the stream when printed."
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  (cond ((not (or input-p output-p))
	 (setf input t))
	((not (or input output))
	 (error "File descriptor must be opened either for input or output.")))
  (let ((stream (%make-fd-stream :fd fd
				 :name name
				 :file file
				 :original original
				 :delete-original delete-original
				 :buffering buffering
				 :timeout timeout)))
    (set-routines stream element-type input output input-buffer-p)
    (when (and auto-close (fboundp 'finalize))
      (finalize stream
		#'(lambda ()
		    (unix:unix-close fd)
		    (format *terminal-io* "** Closed file descriptor ~D~%"
			    fd))))
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    stream))

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;;; PICK-PACKUP-NAME -- internal
;;;
;;; Pick a name to use for the backup file.
;;;
(defvar *backup-extension* ".BAK"
  "This is a string that OPEN tacks on the end of a file namestring to produce
   a name for the :if-exists :rename-and-delete and :rename options.  Also,
   this can be a function that takes a namestring and returns a complete
   namestring.")
;;;
(defun pick-backup-name (name)
  (declare (type simple-string name))
  (let ((ext *backup-extension*))
    (etypecase ext
      (simple-string (concatenate 'simple-string name ext))
      (function (funcall ext name)))))
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;;; ASSURE-ONE-OF -- internal
;;;
;;; Assure that the given arg is one of the given list of valid things.
;;; Allow the user to fix any problems.
;;; 
(defun assure-one-of (item list what)
  (unless (member item list)
    (loop
      (cerror "Enter new value for ~*~S"
	      "~S is invalid for ~S. Must be one of~{ ~S~}"
	      item
	      what
	      list)
      (format (the stream *query-io*) "Enter new value for ~S: " what)
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      (force-output *query-io*)
      (setf item (read *query-io*))
      (when (member item list)
	(return))))
  item)

;;; DO-OLD-RENAME  --  Internal
;;;
;;;    Rename Namestring to Original.  First, check if we have write access,
;;; since we don't want to trash unwritable files even if we technically can.
;;; We return true if we suceed in renaming.
;;;
(defun do-old-rename (namestring original)
  (unless (unix:unix-access namestring unix:w_ok)
    (cerror "Try to rename it anyway." "File ~S is not writable." namestring))
  (multiple-value-bind
      (okay err)
      (unix:unix-rename namestring original)
    (cond (okay t)
	  (t
	   (cerror "Use :SUPERSEDE instead."
		   "Could not rename ~S to ~S: ~A."
		   namestring
		   original
		   (unix:get-unix-error-msg err))
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;;; OPEN -- public
;;;
;;;   Open the given file.
;;;
(defun open (filename
	     &key
	     (direction :input)
	     (element-type 'base-char)
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	     (if-exists nil if-exists-given)
	     (if-does-not-exist nil if-does-not-exist-given))
  "Return a stream which reads from or writes to Filename.
  Defined keywords:
   :direction - one of :input, :output, :io, or :probe
   :element-type - Type of object to read or write, default BASE-CHAR
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   :if-exists - one of :error, :new-version, :rename, :rename-and-delete,
                       :overwrite, :append, :supersede or nil
   :if-does-not-exist - one of :error, :create or nil
  See the manual for details."
  ;; First, make sure that DIRECTION is valid. Allow it to be changed if not.
  (setf direction
	(assure-one-of direction
		       '(:input :output :io :probe)
		       :direction))

  ;; Calculate useful stuff.
  (multiple-value-bind
      (input output mask)
      (case direction
	(:input (values t nil unix:o_rdonly))
	(:output (values nil t unix:o_wronly))
	(:io (values t t unix:o_rdwr))
	(:probe (values t nil unix:o_rdonly)))
    (declare (type index mask))
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    (let* ((pathname (pathname filename))
	   (namestring (unix-namestring pathname input)))
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      ;; Process if-exists argument if we are doing any output.
      (cond (output
	     (unless if-exists-given
	       (setf if-exists
		     (if (eq (pathname-version pathname) :newest)
		       :new-version
		       :error)))
	     (setf if-exists
		   (assure-one-of if-exists
				  '(:error :new-version :rename
				    :rename-and-delete :overwrite
				    :append :supersede nil)
				  :if-exists))
	     (case if-exists
	       ((:error nil)
		(setf mask (logior mask unix:o_excl)))
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	       ((:rename :rename-and-delete)
		(setf mask (logior mask unix:o_creat)))
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	       ((:new-version :supersede)
		(setf mask (logior mask unix:o_trunc)))
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	       (:append
		(setf mask (logior mask unix:o_append)))))
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	    (t
	     (setf if-exists :ignore-this-arg)))
      
      (unless if-does-not-exist-given
	(setf if-does-not-exist
	      (cond ((eq direction :input) :error)
		    ((and output
			  (member if-exists '(:overwrite :append)))
		     :error)
		    ((eq direction :probe)
		     nil)
		    (t
		     :create))))
      (setf if-does-not-exist
	    (assure-one-of if-does-not-exist
			   '(:error :create nil)
			   :if-does-not-exist))
      (if (eq if-does-not-exist :create)
	(setf mask (logior mask unix:o_creat)))
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      (let ((original (if (member if-exists
				  '(:rename :rename-and-delete))
			  (pick-backup-name namestring)))
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	    (delete-original (eq if-exists :rename-and-delete))
	    (mode #o666))
	(when original
	  ;; We are doing a :rename or :rename-and-delete.
	  ;; Determine if the file already exists, make sure the original
	  ;; file is not a directory and keep the mode
	  (let ((exists
		 (and namestring
		      (multiple-value-bind
			  (okay err/dev inode orig-mode)
			  (unix:unix-stat namestring)
			(declare (ignore inode)
				 (type (or index null) orig-mode))
			(cond
			 (okay
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			  (when (and output (= (logand orig-mode #o170000)
					       #o40000))
			    (error "Cannot open ~S for output: Is a directory."
				   namestring))
			  (setf mode (logand orig-mode #o777))
			  t)
			 ((eql err/dev unix:enoent)
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			  nil)
			 (t
			  (error "Cannot find ~S: ~A"
				 namestring
				 (unix:get-unix-error-msg err/dev))))))))
	    (unless (and exists
			 (do-old-rename namestring original))
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	      (setf original nil)
	      (setf delete-original nil)
	      ;; In order to use SUPERSEDE instead, we have
	      ;; to make sure unix:o_creat corresponds to
	      ;; if-does-not-exist.  unix:o_creat was set
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	      ;; before because of if-exists being :rename.
	      (unless (eq if-does-not-exist :create)
		(setf mask (logior (logandc2 mask unix:o_creat) unix:o_trunc)))
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	      (setf if-exists :supersede))))
	
	;; Okay, now we can try the actual open.
	(loop
	  (multiple-value-bind
	      (fd errno)
		  (unix:unix-open namestring mask mode)
		  (values nil unix:enoent))
	    (cond ((numberp fd)
		   (return
		    (case direction
		      ((:input :output :io)
		       (make-fd-stream fd
				       :input input
				       :output output
				       :element-type element-type
				       :file namestring
				       :original original
				       :delete-original delete-original
				       :input-buffer-p t
				       :auto-close t))
		      (:probe
		       (let ((stream
			      (%make-fd-stream :name namestring :fd fd
					       :element-type element-type)))
			 (close stream)
			 stream)))))
		  ((eql errno unix:enoent)
		   (case if-does-not-exist
		     (:error
		      (cerror "Return NIL."
			      "Error opening ~S, ~A."
			      pathname
			      (unix:get-unix-error-msg errno)))
		     (:create
		      (cerror "Return NIL."
			      "Error creating ~S, path does not exist."
			      pathname)))
		   (return nil))
		  ((eql errno unix:eexist)
		   (unless (eq nil if-exists)
		     (cerror "Return NIL."
			     "Error opening ~S, ~A."
			     pathname
			     (unix:get-unix-error-msg errno)))
		  ((eql errno unix:eacces)
		   (cerror "Try again."
			  "Error opening ~S, ~A."
			  pathname
			  (unix:get-unix-error-msg errno)))
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		   (cerror "Return NIL."
			   "Error opening ~S, ~A."
			   pathname
			   (unix:get-unix-error-msg errno))
		   (return nil)))))))))
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;;;; Initialization.

(defvar *tty* nil
  "The stream connected to the controlling terminal or NIL if there is none.")
(defvar *stdin* nil
  "The stream connected to the standard input (file descriptor 0).")
(defvar *stdout* nil
  "The stream connected to the standard output (file descriptor 1).")
(defvar *stderr* nil
  "The stream connected to the standard error output (file descriptor 2).")

;;; STREAM-INIT -- internal interface
;;;
;;; Called when the cold load is first started up.
;;; 
(defun stream-init ()
  (stream-reinit)
  (setf *terminal-io* (make-synonym-stream '*tty*))
  (setf *standard-output* (make-synonym-stream '*stdout*))
  (setf *standard-input*
	(make-two-way-stream (make-synonym-stream '*stdin*)
			     *standard-output*))
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  (setf *error-output* (make-synonym-stream '*stderr*))
  (setf *query-io* (make-synonym-stream '*terminal-io*))
  (setf *debug-io* *query-io*)
  (setf *trace-output* *standard-output*)
  nil)

;;; STREAM-REINIT -- internal interface
;;;
;;; Called whenever a saved core is restarted.
;;; 
(defun stream-reinit ()
  (setf *available-buffers* nil)
  (setf *stdin*
	(make-fd-stream 0 :name "Standard Input" :input t :buffering :line))
  (setf *stdout*
	(make-fd-stream 1 :name "Standard Output" :output t :buffering :line))
  (setf *stderr*
	(make-fd-stream 2 :name "Standard Error" :output t :buffering :line))
  (let ((tty (unix:unix-open "/dev/tty" unix:o_rdwr #o666)))
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    (if tty
	(setf *tty*
	      (make-fd-stream tty :name "the Terminal" :input t :output t
			      :buffering :line :auto-close t))
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	(setf *tty* (make-two-way-stream *stdin* *stdout*))))
  nil)


;;;; Beeping.

(defun default-beep-function (stream)
  (write-char #\bell stream)
  (finish-output stream))

(defvar *beep-function* #'default-beep-function
  "This is called in BEEP to feep the user.  It takes a stream.")

(defun beep (&optional (stream *terminal-io*))
  (funcall *beep-function* stream))


;;; File-Name  --  internal interface
;;;
;;;    Kind of like File-Position, but is an internal hack used by the filesys
;;; stuff to get and set the file name.
;;;
(defun file-name (stream &optional new-name)
  (when (fd-stream-p stream)
    (if new-name
	(setf (fd-stream-file stream) new-name)
	(fd-stream-file stream))))