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     (or (not (eql (fd-stream-ibuf-head stream)
		   (fd-stream-ibuf-tail stream)))
	 (fd-stream-listen stream)
	 (setf (fd-stream-listen stream)
	       (eql (alien:with-alien ((read-fds (alien:struct unix:fd-set)))
		      (unix:fd-zero read-fds)
		      (unix:fd-set (fd-stream-fd stream) read-fds)
		      (unix:unix-fast-select (1+ (fd-stream-fd stream))
					     (alien:addr read-fds) nil nil
					     0 0))
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    (:unread
     (setf (fd-stream-unread stream) arg1)
     (setf (fd-stream-listen stream) t))
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    (:close
     (cond (arg1
	    ;; We got us an abort on our hands.
	    (when (fd-stream-handler stream)
		  (system:remove-fd-handler (fd-stream-handler stream))
		  (setf (fd-stream-handler stream) nil))
	    (when (and (fd-stream-file stream) (fd-stream-obuf-sap stream))
	      (revert-file (fd-stream-file stream)
			   (fd-stream-original stream))))
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	   (t
	    (fd-stream-misc-routine stream :finish-output)
	    (when (fd-stream-delete-original stream)
	      (delete-original (fd-stream-file stream)
			       (fd-stream-original stream)))))
     (when (fboundp 'cancel-finalization)
       (cancel-finalization stream))
     (unix:unix-close (fd-stream-fd stream))
     (when (fd-stream-obuf-sap stream)
       (push (fd-stream-obuf-sap stream) *available-buffers*)
       (setf (fd-stream-obuf-sap stream) nil))
     (when (fd-stream-ibuf-sap stream)
       (push (fd-stream-ibuf-sap stream) *available-buffers*)
       (setf (fd-stream-ibuf-sap stream) nil))
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     (lisp::set-closed-flame stream))
     (setf (fd-stream-unread stream) nil)
     (setf (fd-stream-ibuf-head stream) 0)
     (setf (fd-stream-ibuf-tail stream) 0)
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     (catch 'eof-input-catcher
       (loop
	(multiple-value-bind
	      (count errno)
	    (alien:with-alien ((read-fds (alien:struct unix:fd-set)))
	      (unix:fd-zero read-fds)
	      (unix:fd-set (fd-stream-fd stream) read-fds)
	      (unix:unix-fast-select (1+ (fd-stream-fd stream))
				     (alien:addr read-fds) nil nil 0 0))
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	  (cond ((eql count 1)
		 (do-input stream)
		 (setf (fd-stream-ibuf-head stream) 0)
		 (setf (fd-stream-ibuf-tail stream) 0))
		((and (not count) (eql errno unix:eintr)))
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		(t
		 (return t)))))))
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    (:force-output
     (flush-output-buffer stream))
    (:finish-output
     (flush-output-buffer stream)
     (do ()
	 ((null (fd-stream-output-later stream)))
       (system:serve-all-events)))
    (:element-type
     (fd-stream-element-type stream))
    (:interactive-p
     (unix:unix-isatty (fd-stream-fd stream)))
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    (:line-length
     80)
    (:charpos
     (fd-stream-char-pos stream))
    (:file-length
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     (unless (fd-stream-file stream)
       (error 'simple-type-error
	      :datum stream
	      :expected-type 'file-stream
	      :format-control "~s is not a stream associated with a file."
	      :format-arguments (list stream)))
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     (multiple-value-bind
	 (okay dev ino mode nlink uid gid rdev size
	       atime mtime ctime blksize blocks)
	 (unix:unix-fstat (fd-stream-fd stream))
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       (declare (ignore ino nlink uid gid rdev
			atime mtime ctime blksize blocks))
       (unless okay
	 (error 'simple-file-error
                :format-control "Error fstating ~S: ~A"
		:format-arguments (list stream (unix:get-unix-error-msg dev))))
	   (values (truncate size (fd-stream-element-size stream))))))
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    (:file-position
     (fd-stream-file-position stream arg1))))
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;;; FD-STREAM-FILE-POSITION -- internal.
;;;
(defun fd-stream-file-position (stream &optional newpos)
  (declare (type fd-stream stream)
	   (type (or (integer 0) (member nil :start :end)) newpos))
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  (if (null newpos)
      (system:without-interrupts
	;; First, find the position of the UNIX file descriptor in the file.
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	(multiple-value-bind
	    (unix:unix-lseek (fd-stream-fd stream) 0 unix:l_incr)
	  (declare (type (or (integer 0) null) posn))
	  (cond (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
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		 ;; obviously cannot take into account output we have not
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		 ;; 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 (integer 0) 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 cached 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 '(integer 0))
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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)
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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)
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		    (format *terminal-io* "** Closed ~A~%" name)
		    (when original
		      (revert-file file original)))))
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    stream))

;;; PICK-BACKUP-NAME -- internal
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;;;
;;; 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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;;; NEXT-VERSION -- internal
;;;
;;; Find the next available versioned name for a file.
;;;
(defun next-version (name)
  (declare (type simple-string name))
  (let* ((sep (position #\/ name :from-end t))
	 (base (if sep (subseq name 0 (1+ sep)) ""))
	 (dir (unix:open-dir base)))
    (multiple-value-bind (name type version)
	(extract-name-type-and-version name (if sep (1+ sep) 0) (length name))
      (let ((version (if (symbolp version) 1 (1+ version)))
	    (match (if type
		       (concatenate 'string name "." type ".~")
		       (concatenate 'string name ".~"))))
	(when dir
	  (unwind-protect
	       (loop
		 (let ((name (unix:read-dir dir)))
		   (cond ((null name) (return))
			 ((and (> (length name) (length match))
			       (string= name match :end1 (length match)))
			  (multiple-value-bind (v e)
			      (parse-integer name :start (length match)
						  :junk-allowed t)
			    (when (and v
				       (= (length name) (1+ e))
				       (char= (schar name e) #\~))
			      (setq version (max version (1+ v)))))))))
	    (unix:close-dir dir)))
	(concatenate 'string base
		     match (quick-integer-to-string version) "~")))))

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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.
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;;; We return true if we succeed 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))
;;; FD-OPEN  --  Internal
;;;
;;;    Open a file.
;;;
(defun fd-open (pathname direction if-exists if-exists-given
                          if-does-not-exist if-does-not-exist-given)
  (declare (type pathname pathname)
           (type (member :input :output :io :probe) direction)
           (type (member :error :new-version :rename :rename-and-delete
                         :overwrite :append :supersede nil) if-exists)
           (type (member :error :create nil) if-does-not-exist))
  (multiple-value-bind (input output mask)
      (ecase 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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    ;; 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)))
           (case if-exists
             ((:error nil)
              (setf mask (logior mask unix:o_excl)))
             ((:new-version :rename :rename-and-delete)
              (setf mask (logior mask unix:o_creat)))
             (:supersede
              (setf mask (logior mask unix:o_trunc)))))
          (t
           (setf if-exists nil)))     ; :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))))
    (if (eq if-does-not-exist :create)
        (setf mask (logior mask unix:o_creat)))
    
    (let ((name (cond ((unix-namestring pathname input))
                      ((and input (eq if-does-not-exist :create))
                       (unix-namestring pathname nil)))))
      (let ((original (cond ((eq if-exists :new-version)
			     (next-version name))
			    ((member if-exists '(:rename :rename-and-delete))
			     (pick-backup-name name))))
            (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 name
                      (multiple-value-bind
                            (okay err/dev inode orig-mode)
                          (unix:unix-stat name)
                        (declare (ignore inode)
                                 (type (or index null) orig-mode))
                        (cond
                          (okay
                           (when (and output (= (logand orig-mode #o170000)
                                                #o40000))
                             (error 'simple-file-error
                                 :pathname pathname
                                 :format-control
                                 "Cannot open ~S for output: Is a directory."
                                 :format-arguments (list name)))
                           (setf mode (logand orig-mode #o777))
                           t)
                          ((eql err/dev unix:enoent)
                           nil)
                          (t
                           (error 'simple-file-error
                                  :pathname pathname
                                  :format-control "Cannot find ~S: ~A"
                                  :format-arguments
                                    (list name
                                      (unix:get-unix-error-msg err/dev)))))))))
            (unless (and exists
                         (do-old-rename name original))
              (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
              ;; 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)))
              (setf if-exists :supersede))))
        
        ;; Okay, now we can try the actual open.
        (loop
          (multiple-value-bind (fd errno)
              (if name
                  (unix:unix-open name mask mode)
                  (values nil unix:enoent))
            (cond ((fixnump fd)
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		   (when (eq if-exists :append)
		     (unix:unix-lseek fd 0 unix:l_xtnd)) ; SEEK_END
                   (return (values fd name original delete-original)))
                  ((eql errno unix:enoent)
                   (case if-does-not-exist
                     (:error
                       (cerror "Return NIL."
                               'simple-file-error
                               :pathname pathname
                               :format-control "Error opening ~S, ~A."
                               :format-arguments
                                   (list pathname
                                         (unix:get-unix-error-msg errno))))
                     (:create
                       (cerror "Return NIL."
                               'simple-file-error
                               :pathname pathname
                               :format-control
                                   "Error creating ~S, path does not exist."
                               :format-arguments (list pathname))))
                   (return nil))
                  ((eql errno unix:eexist)
                   (unless (eq nil if-exists)
                     (cerror "Return NIL."
                             'simple-file-error
                             :pathname pathname
                             :format-control "Error opening ~S, ~A."
                             :format-arguments
                                 (list pathname
                                       (unix:get-unix-error-msg errno))))
                   (return nil))
                  ((eql errno unix:eacces)
                   (cerror "Try again."
                           'simple-file-error
                           :pathname pathname
                           :format-control "Error opening ~S, ~A."
                           :format-arguments
                               (list pathname
                                     (unix:get-unix-error-msg errno))))
                  (t
                   (cerror "Return NIL."
                           'simple-file-error
                           :pathname pathname
                           :format-control "Error opening ~S, ~A."
                           :format-arguments
                               (list pathname
                                     (unix:get-unix-error-msg errno)))
                   (return nil)))))))))

;;; OPEN-FD-STREAM  --  Internal
;;;
;;;    Open an fd-stream connected to a file.
;;;
(defun open-fd-stream (pathname &key (direction :input)
				(element-type 'base-char)
				(if-exists nil if-exists-given)
				(if-does-not-exist nil if-does-not-exist-given)
				(external-format :default))
  (declare (type pathname pathname)
           (type (member :input :output :io :probe) direction)
           (type (member :error :new-version :rename :rename-and-delete
                         :overwrite :append :supersede nil) if-exists)
           (type (member :error :create nil) if-does-not-exist)
           (ignore external-format))
  (multiple-value-bind (fd namestring original delete-original)
      (fd-open pathname direction if-exists if-exists-given
	       if-does-not-exist if-does-not-exist-given)
    (when fd
      (case direction
	((:input :output :io)
	 (make-fd-stream fd
			 :input (member direction '(:input :io))
			 :output (member direction '(:output :io))
			 :element-type element-type
			 :file namestring
			 :original original
			 :delete-original delete-original
			 :pathname pathname
			 :input-buffer-p t
			 :auto-close t))
	(:probe
	 (let ((stream (%make-fd-stream :name namestring :fd fd
					:pathname pathname
					:element-type element-type)))
	   (close stream)
	   stream))))))
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;;; OPEN -- public
;;;
;;;   Open the given file.
;;;
(defun open (filename &rest options
		      &key (direction :input)
			   (element-type 'base-char element-type-given)
			   (if-exists nil if-exists-given)
			   (if-does-not-exist nil if-does-not-exist-given)
			   (external-format :default)
			   class mapped input-handle output-handle
		      &allow-other-keys
		      &aux ; Squelch assignment warning.
		      (direction direction)
		      (if-does-not-exist if-does-not-exist)
		      (if-exists if-exists))
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  "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
   :external-format - :default
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  See the manual for details."
  (declare (ignore external-format input-handle output-handle))

  ;; OPEN signals a file-error if the filename is wild.
  (when (wild-pathname-p filename)
    (error 'file-error :pathname filename))
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  ;; First, make sure that DIRECTION is valid. Allow it to be changed if not.
  (setq direction
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	(assure-one-of direction
		       '(:input :output :io :probe)
		       :direction))
  (setf (getf options :direction) direction)
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  (when (and if-exists-given (member direction '(:output :io)))
    (setq if-exists
	  (assure-one-of if-exists
			 '(:error :new-version :rename
			   :rename-and-delete :overwrite
			   :append :supersede nil)
			 :if-exists))
    (setf (getf options :if-exists) if-exists))

  (when if-does-not-exist-given
    (setq if-does-not-exist
	  (assure-one-of if-does-not-exist
			 '(:error :create nil)
			 :if-does-not-exist))
    (setf (getf options :if-does-not-exist) if-does-not-exist))

  (let ((filespec (pathname filename))
	(options (copy-list options))
	(class (or class 'fd-stream)))
    (cond ((eq class 'fd-stream)
	   (remf options :class)
           (remf options :mapped)
           (remf options :input-handle)
           (remf options :output-handle)
           (apply #'open-fd-stream filespec options))
	  ((subtypep class 'stream:simple-stream)
	   (when element-type-given
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             (cerror "Do it anyway."
		     "Can't create simple-streams with an element-type."))
           (when (and (eq class 'stream:file-simple-stream) mapped)
             (setq class 'stream:mapped-file-simple-stream)
             (setf (getf options :class) 'stream:mapped-file-simple-stream))
           (when (subtypep class 'stream:file-simple-stream)
             (when (eq direction :probe)
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               (setq class 'stream:probe-simple-stream)))
           (apply #'make-instance class :filename filespec options))
	  ((subtypep class 'ext:fundamental-stream)
	   (remf options :class)
           (remf options :mapped)
           (remf options :input-handle)
           (remf options :output-handle)
	   (let ((stream (apply #'open-fd-stream filespec options)))
	     (when stream
	       (make-instance class :lisp-stream stream))))
	  (t
	   (error "Unable to open streams of class ~S." class)))))
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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*))
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  (setf *debug-io* *query-io*)
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  (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 (and (not *batch-mode*)
		  (unix:unix-open "/dev/tty" unix:o_rdwr #o666))))
    (setf *tty*
	  (if tty
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	      (make-fd-stream tty :name "the Terminal" :input t :output t
			      :buffering :line :auto-close t)
	      (make-two-way-stream *stdin* *stdout*))))
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  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)
  (typecase stream
    (stream:simple-stream
     (if new-name
	 (stream::%file-rename stream new-name)
	 (stream::%file-name stream)))
    (fd-stream
     (cond (new-name
	    (setf (fd-stream-pathname stream) new-name)
	    (setf (fd-stream-file stream)
		  (unix-namestring new-name nil))
	    t)
	   (t
	    (fd-stream-pathname stream))))))

;;;; Degenerate international character support:

(defun file-string-length (stream object)
  (declare (type (or string character) object)
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	   (type (or file-stream broadcast-stream stream:simple-stream) stream))
  "Return the delta in Stream's FILE-POSITION that would be caused by writing
   Object to Stream.  Non-trivial only in implementations that support
   international character sets."
  (typecase stream
    (stream:simple-stream (stream::%file-string-length stream object))
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    (broadcast-stream
     ;; CLHS says we must return 1 in this case
     1)
    (t
     (etypecase object
       (character 1)
       (string (length object))))))