From: Arun Isaac <arunisaac@systemreboot.net>
To: "Maxime Devos" <maximedevos@telenet.be>,
"Ludovic Courtès" <ludo@gnu.org>
Cc: Guix Devel <guix-devel@gnu.org>
Subject: Re: Move switch-symlinks to (guix build utils)
Date: Mon, 06 Jun 2022 16:57:49 +0530 [thread overview]
Message-ID: <87czfmm3pm.fsf@systemreboot.net> (raw)
In-Reply-To: <2c194c3b2f192ba49caaf585703f95b6c6bcb7d9.camel@telenet.be>
> Maybe replace
>
> (symlink target pivot)
>
> by (symlink/remove-old target pivot)
>
> where
>
> (define (symlink/remove-old target link)
> "Make a symbolic link named LINK pointing to TARGET.
> If LINK already exists, it will be removed first.
> This is not an atomic operation."
> (catch 'system-error
> (lambda ()
> (symlink target link))
> (lambda stuff
> (if (= (system-error-errno stuff) EEXIST)
> (begin
> ;; remove old link and retry
> (delete-file link)
> (symlink/remove-old link target))
> (apply throw stuff)))))
>
> ?
Could we implement symlink/remove-old without catch and throw? Something
like:
--8<---------------cut here---------------start------------->8---
(define (symlink/remove-old target link)
"Make a symbolic link named LINK pointing to TARGET. If LINK already
exists, it will be removed first. This is not an atomic operation."
(when (file-exists? link)
(delete-file link))
(symlink target link))
--8<---------------cut here---------------end--------------->8---
We might also inline this into switch-symlinks like so.
--8<---------------cut here---------------start------------->8---
(define (switch-symlinks link target)
"Atomically switch LINK, a symbolic link, to point to TARGET. Works
both when LINK already exists and when it does not."
(let ((pivot (string-append link ".new")))
;; Delete pivot link in case it already exists. This can happen if
;; a previous switch-symlinks was interrupted.
(when (file-exists? pivot)
(delete-file pivot))
(symlink target pivot)
(rename-file pivot link)))
--8<---------------cut here---------------end--------------->8---
WDYT?
next prev parent reply other threads:[~2022-06-06 11:52 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-01 7:34 Move switch-symlinks to (guix build utils) Arun Isaac
2022-06-01 12:09 ` Maxime Devos
2022-06-02 15:06 ` Arun Isaac
2022-06-02 15:13 ` Maxime Devos
2022-06-03 16:38 ` Ludovic Courtès
2022-06-03 17:09 ` Maxime Devos
2022-06-03 19:30 ` Ludovic Courtès
2022-06-03 19:30 ` Ludovic Courtès
2022-06-03 23:55 ` bokr
2022-06-04 10:17 ` Maxime Devos
2022-06-06 11:27 ` Arun Isaac [this message]
2022-06-06 12:20 ` Maxime Devos
2022-06-08 20:12 ` Arun Isaac
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