home: services: Fix race condition when detecting first login.

* gnu/home/services.scm (compute-on-first-login-script): Use open-fdes to
atomically check whether a file exists and create it if not.

Co-authored-by: Ludovic Courtès <ludo@gnu.org>
This commit is contained in:
Carlo Zancanaro 2023-10-11 22:57:19 +11:00 committed by Ludovic Courtès
parent b25185849f
commit 6b0a321969
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@ -2,6 +2,7 @@
;;; Copyright © 2021-2023 Andrew Tropin <andrew@trop.in>
;;; Copyright © 2021 Xinglu Chen <public@yoctocell.xyz>
;;; Copyright © 2022-2023 Ludovic Courtès <ludo@gnu.org>
;;; Copyright © 2023 Carlo Zancanaro <carlo@zancanaro.id.au>
;;;
;;; This file is part of GNU Guix.
;;;
@ -412,20 +413,29 @@ activation.")))
#~(begin
(use-modules (guix i18n)
(guix diagnostics))
(define (claim-first-run file)
(catch #t
(lambda ()
;; This incantation raises an error if FILE already exists, and
;; creates it otherwise.
(close-fdes
(open-fdes file (logior O_CREAT O_EXCL O_CLOEXEC)))
#t)
(const #f)))
#$%initialize-gettext
(let* ((xdg-runtime-dir (or (getenv "XDG_RUNTIME_DIR")
(format #f "/run/user/~a" (getuid))))
(flag-file-path (string-append
xdg-runtime-dir "/on-first-login-executed"))
(touch (lambda (file-name)
(call-with-output-file file-name (const #t)))))
xdg-runtime-dir "/on-first-login-executed")))
;; XDG_RUNTIME_DIR dissapears on logout, that means such trick
;; allows to launch on-first-login script on first login only
;; after complete logout/reboot.
(if (file-exists? xdg-runtime-dir)
(unless (file-exists? flag-file-path)
(begin #$@gexps (touch flag-file-path)))
(when (claim-first-run flag-file-path)
#$@gexps)
;; TRANSLATORS: 'on-first-login' is the name of a service and
;; shouldn't be translated
(warning (G_ "XDG_RUNTIME_DIR doesn't exists, on-first-login script