From: Leo Prikler <leo.prikler@student.tugraz.at>
To: "Ludovic Courtès" <ludo@gnu.org>
Cc: 45570@debbugs.gnu.org, conjaroy@gmail.com
Subject: bug#45570: [PATCH] system: Assert, that user and group names are unique.
Date: Wed, 06 Jan 2021 13:34:26 +0100 [thread overview]
Message-ID: <e1f7d49f48db237ece4527a8ee5236a8bfa629e7.camel@student.tugraz.at> (raw)
In-Reply-To: <87v9cao0c8.fsf@gnu.org>
Hi,
Am Mittwoch, den 06.01.2021, 10:56 +0100 schrieb Ludovic Courtès:
> Hi,
>
> Leo Prikler <leo.prikler@student.tugraz.at> skribis:
>
> > *gnu/system/shadow.scm (find-duplicates): New variable.
> > (assert-unique-account-names, assert-unique-group-names): New
> > variables.
> > (account-activation): Use them here.
>
> [...]
>
> > +(define (find-duplicates list =)
> > + (match list
> > + ('() '())
>
> This should be:
>
> (match list
> (() '())
> …)
>
> I’m surprised '() works as a pattern.
I think it's because matching literals works, but you're right.
> > + ((first . rest)
> > + (if (member first rest =) ; (srfi srfi-1) member
> > + (cons first (find-duplicates rest =))
> > + (find-duplicates rest =)))))
>
> Note that this is quadratic; it’s fine as long as we don’t have “too
> many” users, which may be the case in general.
It is indeed quadratic, but would there even be an n log n solution?
I've once done an n log n sort+delete-duplicates!, perhaps that'd be a
nicer solution here?
> > +(define (assert-unique-account-names users)
> > + (for-each
> > + (lambda (account)
> > + (raise (condition
> > + (&message
> > + (message
> > + (format #f (G_ "account with name '~a' found
> > twice.")
> > + (user-account-name account)))))))
> > + (find-duplicates users (lambda (alice bob)
> > + (string=? (user-account-name alice)
> > + (user-account-name bob))))))
>
> ‘for-each’ looks awkward since we’ll stop on the first one. How
> about
> something like:
>
> (define (assert-unique-account-names users)
> (match (find-duplicates things …)
> (() #t)
> (lst
> (raise (formatted-message (G_ "the following accounts appear
> more than once:~{ ~a~}~%"
> lst))))))
>
> ?
That'd be weird for duplicate duplicates, hence just reporting the
first. Of course we could always count occurrences by allocating a
local hash table and then do some fancy hash-map->list conversion. If
we do use hash-tables, perhaps this could even be a linear algorithm?
Regards,
Leo
next prev parent reply other threads:[~2021-01-06 12:35 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-31 18:14 bug#45570: operating-system definitions allow duplicate passwd and group entries Jason Conroy
2021-01-01 11:13 ` bug#45570: [PATCH] system: Assert, that user and group names are unique Leo Prikler
2021-01-02 1:16 ` Danny Milosavljevic
2021-01-02 5:57 ` Leo Prikler
2021-01-06 9:56 ` Ludovic Courtès
2021-01-06 12:34 ` Leo Prikler [this message]
2021-01-06 13:32 ` Ludovic Courtès
2021-01-06 21:00 ` Leo Prikler
2021-01-07 8:29 ` Ludovic Courtès
2021-01-06 21:21 ` bug#45570: [PATCH v2] " Leo Prikler
2021-01-07 8:35 ` Ludovic Courtès
2021-01-07 11:13 ` Leo Prikler
2021-01-07 11:10 ` bug#45570: [PATCH v3] " Leo Prikler
2021-01-11 13:09 ` Ludovic Courtès
2021-01-11 15:06 ` Leo Prikler
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