113 lines
3.8 KiB
Scheme
113 lines
3.8 KiB
Scheme
;;; Ops that create objects in the file system:
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;;; create-{directory,fifo,hard-link,symlink}
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;;; Copyright (c) 1993 by Olin Shivers.
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;;; This procedure nukes FNAME, whatever it may be: directory, file, fifo,
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;;; symlink.
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;;;
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;;; We can't probe FNAME to find out what it is and then do the right
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;;; delete operation because there's a window in-between the probe and the
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;;; delete where the file system can be altered -- the probe and delete
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;;; aren't atomic. In order to deliver on our contract, we have to spin
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;;; in a funny loop until we win. In practice, the loop will probably never
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;;; execute more than once.
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(define (delete-filesys-object fname)
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(let loop ()
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(or (with-errno-handler ; Assume it's a file and try.
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((err data)
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((errno/perm) #f) ; Return #f if directory
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((errno/noent) #t))
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(delete-file fname)
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#t)
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(with-errno-handler ; Assume it's a directory and try.
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((err data)
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((errno/notdir) #f) ; Return #f if fname is not a directory.
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((errno/noent) #t))
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(delete-directory fname)
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#t)
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(loop)))) ; Strange things are happening. Try again.
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;;; For similar reasons, all of these ops must loop.
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;;; Abstract out common code for create-{directory,fifo,hard-link,symlink}:
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(define (create-file-thing fname makeit override? op-name syscall)
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(let ((query (lambda ()
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(y-or-n? (string-append op-name ": " fname
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" already exists. Delete")))))
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(let loop ((override? override?))
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;; MAKEIT returns #f if win, errno if lose.
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(cond ((makeit fname) =>
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(lambda (err)
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(if (not (= err errno/exist))
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(errno-error err syscall fname)
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;; FNAME exists. Nuke it and retry?
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(cond ((if (eq? override? 'query)
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(query)
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override?)
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(delete-filesys-object fname)
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(loop #t))
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(else
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(errno-error err syscall fname))))))))))
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;;;;;;;
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(define (create-directory dir . rest)
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(let ((perms (if (null? rest) #o777 (car rest)))
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(override? (if (or (null? rest) (null? (cdr rest))) #f
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(cadr rest))))
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(create-file-thing dir
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(lambda (dir) (create-directory/errno dir perms))
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override?
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"create-directory"
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create-directory)))
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(define (create-fifo fifo . rest)
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(let ((perms (if (null? rest) #o777 (car rest)))
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(override? (if (or (null? rest) (null? (cdr rest))) #f
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(cadr rest))))
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(create-file-thing fifo
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(lambda (fifo) (create-fifo/errno fifo perms))
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override?
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"create-fifo"
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create-fifo)))
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(define (create-hard-link old-fname new-fname . maybe-override?)
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(create-file-thing new-fname
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(lambda (new-fname)
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(create-hard-link/errno old-fname new-fname))
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(:optional maybe-override? #f)
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"create-hard-link"
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create-hard-link))
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(define (create-symlink old-fname new-fname . maybe-override?)
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(create-file-thing new-fname
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(lambda (symlink)
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(create-symlink/errno old-fname symlink))
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(:optional maybe-override? #f)
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"create-symlink"
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create-symlink))
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;;; Unix rename() works backwards from mkdir(), mkfifo(), link(), and
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;;; symlink() -- it overrides by default, (though insisting on a type
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;;; match between the old and new object). So we can't use create-file-thing.
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;;; Note that this loop has a tiny atomicity problem -- if someone
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;;; creates a file *after* we do our existence check, but *before* we
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;;; do the rename, we could end up overriding it, when the user asked
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;;; us not to. That's life in the food chain.
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(define (rename-file old-fname new-fname . maybe-override?)
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(let ((override? (:optional maybe-override? #f)))
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(if (or (and override? (not (eq? override? 'query)))
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(file-not-exists? new-fname)
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(and override?
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(y-or-n? (string-append "rename-file:" new-fname
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" already exists. Delete"))))
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(%rename-file old-fname new-fname))))
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