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  (with-alien ((buf (struct stat)))
    (syscall ("lstat" c-string (* (struct stat)))
	     (extract-stat-results buf)
	     name (addr buf))))

(defun unix-fstat (fd)
  "Unix-fstat is similar to unix-stat except the file is specified
   by the file descriptor fd."
  (declare (type unix-fd fd))
  (with-alien ((buf (struct stat)))
    (syscall ("fstat" int (* (struct stat)))
	     (extract-stat-results buf)
	     fd (addr buf))))


(defconstant rusage_self 0 "The calling process.")
(defconstant rusage_children -1 "Terminated child processes.")

(defun unix-getrusage (who)
  "Unix-getrusage returns information about the resource usage
   of the process specified by who.  Who can be either the
   current process (rusage_self) or all of the terminated
   child processes (rusage_children).  NIL and an error number
   is returned if the call fails."
  (with-alien ((usage (struct rusage)))
    (syscall ("getrusage" int (* (struct rusage)))
	     (values t
		     (+ (* (slot (slot usage 'ru-utime) 'tv-sec) 1000000)
			(slot (slot usage 'ru-utime) 'tv-usec))
		     (+ (* (slot (slot usage 'ru-stime) 'tv-sec) 1000000)
			(slot (slot usage 'ru-stime) 'tv-usec))
		     (slot usage 'ru-maxrss)
		     (slot usage 'ru-ixrss)
		     (slot usage 'ru-idrss)
		     (slot usage 'ru-isrss)
		     (slot usage 'ru-minflt)
		     (slot usage 'ru-majflt)
		     (slot usage 'ru-nswap)
		     (slot usage 'ru-inblock)
		     (slot usage 'ru-oublock)
		     (slot usage 'ru-msgsnd)
		     (slot usage 'ru-msgrcv)
		     (slot usage 'ru-nsignals)
		     (slot usage 'ru-nvcsw)
		     (slot usage 'ru-nivcsw))
	     who (addr usage))))

(defun unix-gettimeofday ()
  "If it works, unix-gettimeofday returns 5 values: T, the seconds and
   microseconds of the current time of day, the timezone (in minutes west
   of Greenwich), and a daylight-savings flag.  If it doesn't work, it
   returns NIL and the errno."
  (with-alien ((tv (struct timeval))
	       (tz (struct timezone)))
    (syscall ("gettimeofday" (* (struct timeval)) (* (struct timezone)))
	     (values T
		     (slot tv 'tv-sec)
		     (slot tv 'tv-usec)
		     (slot tz 'tz-minuteswest)
		     (slot tz 'tz-dsttime))
	     (addr tv)
	     (addr tz))))

;;; Unix-utimes changes the accessed and updated times on UNIX
;;; files.  The first argument is the filename (a string) and
;;; the second argument is a list of the 4 times- accessed and
;;; updated seconds and microseconds.

(defun unix-utimes (file atime-sec atime-usec mtime-sec mtime-usec)
  "Unix-utimes sets the 'last-accessed' and 'last-updated'
   times on a specified file.  NIL and an error number is
   returned if the call is unsuccessful."
  (declare (type unix-pathname file)
	   (type (alien unsigned-long)
		 atime-sec atime-usec
		 mtime-sec mtime-usec))
  (with-alien ((tvp (array (struct timeval) 2)))
    (setf (slot (deref tvp 0) 'tv-sec) atime-sec)
    (setf (slot (deref tvp 0) 'tv-usec) atime-usec)
    (setf (slot (deref tvp 1) 'tv-sec) mtime-sec)
    (setf (slot (deref tvp 1) 'tv-usec) mtime-usec)
    (void-syscall ("utimes" c-string (* (struct timeval)))
		  file
		  (cast tvp (* (struct timeval))))))

;;; Unix-setreuid sets the real and effective user-id's of the current
;;; process to the arguments "ruid" and "euid", respectively.  Usage is
;;; restricted for anyone but the super-user.  Setting either "ruid" or
;;; "euid" to -1 makes the system use the current id instead.

(defun unix-setreuid (ruid euid)
  "Unix-setreuid sets the real and effective user-id's of the current
   process to the specified ones.  NIL and an error number is returned
   if the call fails."
  (void-syscall ("setreuid" int int) ruid euid))

;;; Unix-setregid sets the real and effective group-id's of the current
;;; process to the arguments "rgid" and "egid", respectively.  Usage is
;;; restricted for anyone but the super-user.  Setting either "rgid" or
;;; "egid" to -1 makes the system use the current id instead.

(defun unix-setregid (rgid egid)
  "Unix-setregid sets the real and effective group-id's of the current
   process process to the specified ones.  NIL and an error number is
   returned if the call fails."
  (void-syscall ("setregid" int int) rgid egid))

(def-alien-routine ("getpid" unix-getpid) int
  "Unix-getpid returns the process-id of the current process.")

(def-alien-routine ("getppid" unix-getppid) int
  "Unix-getppid returns the process-id of the parent of the current process.")

(def-alien-routine ("getgid" unix-getgid) int
  "Unix-getgid returns the real group-id of the current process.")

(def-alien-routine ("getegid" unix-getegid) int
  "Unix-getegid returns the effective group-id of the current process.")

;;; Unix-getpgrp returns the group-id associated with the
;;; process whose process-id is specified as an argument.
;;; As usual, if the process-id is 0, it refers to the current
;;; process.

(defun unix-getpgrp (pid)
  "Unix-getpgrp returns the group-id of the process associated
   with pid."
  (int-syscall ("getpgrp" int) pid))

;;; Unix-setpgrp sets the group-id of the process specified by 
;;; "pid" to the value of "pgrp".  The process must either have
;;; the same effective user-id or be a super-user process.

(defun unix-setpgrp (pid pgrp)
  "Unix-setpgrp sets the process group on the process pid to
   pgrp.  NIL and an error number is returned upon failure."
  (void-syscall ("setpgrp" int int) pid pgrp))

(def-alien-routine ("getuid" unix-getuid) int
  "Unix-getuid returns the real user-id associated with the
   current process.")

;;; Unix-getpagesize returns the number of bytes in the system page.

(defun unix-getpagesize ()
  "Unix-getpagesize returns the number of bytes in a system page."
  (int-syscall ("getpagesize")))

(defun unix-gethostname ()
  "Unix-gethostname returns the name of the host machine as a string."
  (with-alien ((buf (array char 256)))
    (syscall ("gethostname" (* char) int)
	     (cast buf c-string)
	     (cast buf (* char)) 256)))

(def-alien-routine ("gethostid" unix-gethostid) unsigned-long
  "Unix-gethostid returns a 32-bit integer which provides unique
   identification for the host machine.")

(def-alien-routine ("fork" unix-fork) int
  "Executes the unix fork system call.  Returns 0 in the child and the pid
  of the child in the parent if it works, or -1 if it doesn't work.")


;;; Operations on Unix Directories.

(export '(open-dir read-dir close-dir))

(defstruct (directory
	    (:print-function %print-directory))
  name
  (dir-struct (required-argument) :type system-area-pointer))

(defun %print-directory (dir stream depth)
  (declare (ignore depth))
  (format stream "#<Directory ~S>" (directory-name dir)))

(defun open-dir (pathname)
  (declare (type unix-pathname pathname))
  (let ((kind (unix-file-kind pathname)))
    (case kind
      (:directory
       (let ((dir-struct
	      (alien-funcall (extern-alien "opendir"
					   (function system-area-pointer
						     c-string))
			     pathname)))
	 (if (zerop (sap-int dir-struct))
	     (values nil unix-errno)
	     (make-directory :name pathname :dir-struct dir-struct))))
      ((nil)
       (values nil enoent))
      (t
       (values nil enotdir)))))

(defun read-dir (dir)
  (declare (type directory dir))
  (let ((daddr (alien-funcall (extern-alien "readdir"
					    (function system-area-pointer
						      system-area-pointer))
			      (directory-dir-struct dir))))
    (declare (type system-area-pointer daddr))
    (if (zerop (sap-int daddr))
	nil
	(with-alien ((direct (* (struct direct)) daddr))
	  (let ((nlen (slot direct 'd-namlen))
		(ino (slot direct 'd-ino)))
	    (declare (type (unsigned-byte 16) nlen))
	    (let ((string (make-string nlen)))
	      (kernel:copy-from-system-area
	       (alien-sap (addr (slot direct 'd-name))) 0
	       string (* vm:vector-data-offset vm:word-bits)
	       (* nlen vm:byte-bits))
	      (values string ino)))))))

(defun close-dir (dir)
  (declare (type directory dir))
  (alien-funcall (extern-alien "closedir"
			       (function void system-area-pointer))
		 (directory-dir-struct dir))
  nil)


(defun unix-current-directory ()
  (with-alien ((buf (array char 1024)))
    (values (not (zerop (alien-funcall (extern-alien "getwd"
						     (function int (* char)))
				       (cast buf (* char)))))
	    (cast buf c-string))))



;;;; Support routines for dealing with unix pathnames.

(export '(unix-file-kind unix-maybe-prepend-current-directory
	  unix-resolve-links unix-simplify-pathname))

(defun unix-file-kind (name &optional check-for-links)
  "Returns either :file, :directory, :link, :special, or NIL."
  (declare (simple-string name))
  (multiple-value-bind (res dev ino mode)
		       (if check-for-links
			   (unix-lstat name)
			   (unix-stat name))
    (declare (type (or fixnum null) mode)
	     (ignore dev ino))
    (when res
      (let ((kind (logand mode s-ifmt)))
	(cond ((eql kind s-ifdir) :directory)
	      ((eql kind s-ifreg) :file)
	      ((eql kind s-iflnk) :link)
	      (t :special))))))

(defun unix-maybe-prepend-current-directory (name)
  (declare (simple-string name))
  (if (and (> (length name) 0) (char= (schar name 0) #\/))
      name
      (multiple-value-bind (win dir) (unix-current-directory)
	(if win
	    (concatenate 'simple-string dir "/" name)
	    name))))

(defun unix-resolve-links (pathname)
  "Returns the pathname with all symbolic links resolved."
  (declare (simple-string pathname))
  (let ((len (length pathname))
	(pending pathname))
    (declare (fixnum len) (simple-string pending))
    (if (zerop len)
	pathname
	(let ((result (make-string 1024 :initial-element (code-char 0)))
	      (fill-ptr 0)
	      (name-start 0))
	  (loop
	    (let* ((name-end (or (position #\/ pending :start name-start) len))
		   (new-fill-ptr (+ fill-ptr (- name-end name-start))))
	      (replace result pending
		       :start1 fill-ptr
		       :end1 new-fill-ptr
		       :start2 name-start
		       :end2 name-end)
	      (let ((kind (unix-file-kind (if (zerop name-end) "/" result) t)))
		(unless kind (return nil))
		(cond ((eq kind :link)
		       (multiple-value-bind (link err) (unix-readlink result)
			 (unless link
			   (error "Error reading link ~S: ~S"
				  (subseq result 0 fill-ptr)
				  (get-unix-error-msg err)))
			 (cond ((or (zerop (length link))
				    (char/= (schar link 0) #\/))
				;; It's a relative link
				(fill result (code-char 0)
				      :start fill-ptr
				      :end new-fill-ptr))
			       ((string= result "/../" :end1 4)
				;; It's across the super-root.
				(let ((slash (or (position #\/ result :start 4)
						 0)))
				  (fill result (code-char 0)
					:start slash
					:end new-fill-ptr)
				  (setf fill-ptr slash)))
			       (t
				;; It's absolute.
				(and (> (length link) 0)
				     (char= (schar link 0) #\/))
				(fill result (code-char 0) :end new-fill-ptr)
				(setf fill-ptr 0)))
			 (setf pending
			       (if (= name-end len)
				   link
				   (concatenate 'simple-string
						link
						(subseq pending name-end))))
			 (setf len (length pending))
			 (setf name-start 0)))
		      ((= name-end len)
		       (return (subseq result 0 new-fill-ptr)))
		      ((eq kind :directory)
		       (setf (schar result new-fill-ptr) #\/)
		       (setf fill-ptr (1+ new-fill-ptr))
		       (setf name-start (1+ name-end)))
		      (t
		       (return nil))))))))))

(defun unix-simplify-pathname (src)
  (declare (simple-string src))
  (let* ((src-len (length src))
	 (dst (make-string src-len))
	 (dst-len 0)
	 (dots 0)
	 (last-slash nil))
    (macrolet ((deposit (char)
			`(progn
			   (setf (schar dst dst-len) ,char)
			   (incf dst-len))))
      (dotimes (src-index src-len)
	(let ((char (schar src src-index)))
	  (cond ((char= char #\.)
		 (when dots
		   (incf dots))
		 (deposit char))
		((char= char #\/)
		 (case dots
		   (0
		    ;; Either ``/...' or ``...//...'
		    (unless last-slash
		      (setf last-slash dst-len)
		      (deposit char)))
		   (1
		    ;; Either ``./...'' or ``..././...''
		    (decf dst-len))
		   (2
		    ;; We've found ..
		    (cond
		     ((and last-slash (not (zerop last-slash)))
		      ;; There is something before this ..
		      (let ((prev-prev-slash
			     (position #\/ dst :end last-slash :from-end t)))
			(cond ((and (= (+ (or prev-prev-slash 0) 2)
				       last-slash)
				    (char= (schar dst (- last-slash 2)) #\.)
				    (char= (schar dst (1- last-slash)) #\.))
			       ;; The something before this .. is another ..
			       (deposit char)
			       (setf last-slash dst-len))
			      (t
			       ;; The something is some random dir.
			       (setf dst-len
				     (if prev-prev-slash
					 (1+ prev-prev-slash)
					 0))
			       (setf last-slash prev-prev-slash)))))
		     (t
		      ;; There is nothing before this .., so we need to keep it
		      (setf last-slash dst-len)
		      (deposit char))))
		   (t
		    ;; Something other than a dot between slashes.
		    (setf last-slash dst-len)
		    (deposit char)))
		 (setf dots 0))
		(t
		 (setf dots nil)
		 (setf (schar dst dst-len) char)
		 (incf dst-len))))))
    (when (and last-slash (not (zerop last-slash)))
      (case dots
	(1
	 ;; We've got  ``foobar/.''
	 (decf dst-len))
	(2
	 ;; We've got ``foobar/..''
	 (unless (and (>= last-slash 2)
		      (char= (schar dst (1- last-slash)) #\.)
		      (char= (schar dst (- last-slash 2)) #\.)
		      (or (= last-slash 2)
			  (char= (schar dst (- last-slash 3)) #\/)))
	   (let ((prev-prev-slash
		  (position #\/ dst :end last-slash :from-end t)))
	     (if prev-prev-slash
		 (setf dst-len (1+ prev-prev-slash))
		 (return-from unix-simplify-pathname "./")))))))
    (cond ((zerop dst-len)
	   "./")
	  ((= dst-len src-len)
	   dst)
	  (t
	   (subseq dst 0 dst-len)))))


;;;; Other random routines.

(def-alien-routine ("isatty" unix-isatty) boolean
  "Accepts a Unix file descriptor and returns T if the device
  associated with it is a terminal."
  (fd int))

(def-alien-routine ("ttyname" unix-ttyname) c-string
  (fd int))




;;;; UNIX-EXECVE

(defun unix-execve (program &optional arg-list
			    (environment *environment-list*))
  "Executes the Unix execve system call.  If the system call suceeds, lisp
   will no longer be running in this process.  If the system call fails this
   function returns two values: NIL and an error code.  Arg-list should be a
   list of simple-strings which are passed as arguments to the exec'ed program.
   Environment should be an a-list mapping symbols to simple-strings which this
   function bashes together to form the environment for the exec'ed program."
  (check-type program simple-string)
  (let ((env-list (let ((envlist nil))
		    (dolist (cons environment)
		      (push (if (cdr cons)
				(concatenate 'simple-string
					     (string (car cons)) "="
					     (cdr cons))
				(car cons))
			    envlist))
		    envlist)))
    (sub-unix-execve program arg-list env-list)))


(defmacro round-bytes-to-words (n)
  `(logand (the fixnum (+ (the fixnum ,n) 3)) (lognot 3)))

;;;
;;; STRING-LIST-TO-C-STRVEC	-- Internal
;;; 
;;; STRING-LIST-TO-C-STRVEC is a function which takes a list of
;;; simple-strings and constructs a C-style string vector (strvec) --
;;; a null-terminated array of pointers to null-terminated strings.
;;; This function returns two values: a sap and a byte count.  When the
;;; memory is no longer needed it should be deallocated with
;;; vm_deallocate.
;;; 
(defun string-list-to-c-strvec (string-list)
  ;;
  ;; Make a pass over string-list to calculate the amount of memory
  ;; needed to hold the strvec.
  (let ((string-bytes 0)
	(vec-bytes (* 4 (1+ (length string-list)))))
    (declare (fixnum string-bytes vec-bytes))
    (dolist (s string-list)
      (check-type s simple-string)
      (incf string-bytes (round-bytes-to-words (1+ (length s)))))
    ;;
    ;; Now allocate the memory and fill it in.
    (let* ((total-bytes (+ string-bytes vec-bytes))
	   (vec-sap (system:allocate-system-memory total-bytes))
	   (string-sap (sap+ vec-sap vec-bytes))
	   (i 0))
      (declare (type (and unsigned-byte fixnum) total-bytes i)
	       (type system:system-area-pointer vec-sap string-sap))
      (dolist (s string-list)
	(declare (simple-string s))
	(let ((n (length s)))
	  ;; 
	  ;; Blast the string into place
	  (kernel:copy-to-system-area (the simple-string s)
				      (* vm:vector-data-offset vm:word-bits)
				      string-sap 0
				      (* (1+ n) vm:byte-bits))
	  ;; 
	  ;; Blast the pointer to the string into place
	  (setf (sap-ref-sap vec-sap i) string-sap)
	  (setf string-sap (sap+ string-sap (round-bytes-to-words (1+ n))))
	  (incf i)))
      ;; Blast in last null pointer
      (setf (sap-ref-sap vec-sap i) (int-sap 0))
      (values vec-sap total-bytes))))

(defun sub-unix-execve (program arg-list env-list)
  (let ((argv nil)
	(argv-bytes 0)
	(envp nil)
	(envp-bytes 0)
	result error-code)
    (unwind-protect
	(progn
	  ;; Blast the stuff into the proper format
	  (multiple-value-setq
	      (argv argv-bytes)
	    (string-list-to-c-strvec arg-list))
	  (multiple-value-setq
	      (envp envp-bytes)
	    (string-list-to-c-strvec env-list))
	  ;;
	  ;; Now do the system call
	  (multiple-value-setq
	      (result error-code)
	    (int-syscall ("execve"
			  (* char) system-area-pointer system-area-pointer)
			 program argv envp)))
      ;; 
      ;; Deallocate memory
      (when argv
	(system:deallocate-system-memory argv argv-bytes))
      (when envp
	(system:deallocate-system-memory envp envp-bytes)))
    (values result error-code)))



;;;; Socket support.

(def-alien-routine ("socket" unix-socket) int
  (domain int)
  (type int)
  (protocol int))

(def-alien-routine ("connect" unix-connect) int
  (socket int)
  (sockaddr (* t))
  (len int))

(def-alien-routine ("bind" unix-bind) int
  (socket int)
  (sockaddr (* t))
  (len int))

(def-alien-routine ("listen" unix-listen) int
  (socket int)
  (backlog int))

(def-alien-routine ("accept" unix-accept) int
  (socket int)
  (sockaddr (* t))
  (len int :in-out))

(def-alien-routine ("recv" unix-recv) int
  (fd int)
  (buffer c-string)
  (length int)
  (flags int))

(def-alien-routine ("send" unix-send) int
  (fd int)
  (buffer c-string)
  (length int)
  (flags int))