On Sun, Jan 15, 2017 at 11:24:30PM +0100, Ludovic Court??s wrote:
     
     Then maybe this:
     
       (define (file-system-needed-for-boot? fs)
         (or (%file-system-needed-for-boot? fs)
             (and (file-prefix? (file-system-needed-for-boot? fs)
                                (%store-directory))
                  (not (memq 'bind-mount (file-system-flags fs))))))
     
     with:
     
     --8<---------------cut here---------------start------------->8---
     scheme@(guile-user)>   (define (file-prefix? file1 file2)
     			 (define not-slash
     			   (char-set-complement (char-set #\/)))
     			 (and (string-prefix? "/" file1)
     			      (let loop ((file1 (string-tokenize file1 not-slash))
     					 (file2 (string-tokenize file2 not-slash)))
     				(match file1
     				  (()
     				   #t)
     				  ((head1 tail1 ...)
     				   (match file2
     				     ((head2 tail2 ...)
     				      (and (string=? head1 head2)
     					   (loop tail1 tail2)))
     				     (()
     				      #f)))))))
     scheme@(guile-user)> (file-prefix? "/gn" "/gnu/store")
     $13 = #f
     scheme@(guile-user)> (file-prefix? "/gnu/store/foo" "/gnu/store")
     $14 = #f
     scheme@(guile-user)> (file-prefix? "/gnu/store" "/gnu/store")
     $15 = #t
     scheme@(guile-user)> (file-prefix? "/gnu" "/gnu/store")
     $16 = #t
     scheme@(guile-user)> (file-prefix? "/" "/gnu/store")
     $17 = #t
     --8<---------------cut here---------------end--------------->8---
     
     This seems more natural to me than computing the set of prefixes like
     ???all-subpaths??? does.
     
     WDYT?
     
     If that???s fine with you I can commit this.
     

It looks fine to me.  I haven't tested it ....


J'

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