Re: [PATCH] gnu: Mark /gnu/store as needed for boot.

[ludo@gnu.org (Ludovic Courtès)]

John Darrington <john@darrington.wattle.id.au> skribis:

> On Sat, Jan 14, 2017 at 10:30:43PM +0100, Ludovic Court??s wrote:
>      
>      > * gnu/system/file-systems.scm (all-subpaths): New procedure.
>      > (file-system-needed-for-boot?): Use it to check for ancestors
>      > of %store-directory.
>      
>      I guess the idea is to have ???needed-for-boot???? automatically set for
>      users who store /gnu or /gnu/store on a separate partition, right?
>
> Correct.
>      
>      The problem is that we need to exclude bind mounts, as done in
>      ???store-file-system??? in (gnu system).
>
> Thanks for pointing that out.
>      
>      What about:
>      
>        (define (file-system-needed-for-boot? fs)
>          (or (%file-system-needed-for-boot? fs)
>              (and (string-prefix? (file-system-mount-point fs) (%store-directory))
>                   (not (memq 'bind-mount (file-system-flags fs))))))
>      
>
> Perhaps I am misunderstanding something, but
>
>      (string-prefix? (file-system-mount-point fs) (%store-directory))
>      
> will erroneously return #t when (file-system-mount-point fs) evaluates
> to "/gn"  and (%store-directory) to "/gnu/store".  Will it not???
>
> That is why I wrote a procedure to fix that problem.

Good point.

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.

Thanks!

Ludo’.