bug#50580: GDM doesn't start

[Maxime Devos <maximedevos@telenet.be>]

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Hi,

The GDM service doesn't start anymore.  To test, you can use the attached
xorg-repro.tmpl (guix system vm xorg-repro.tml && run the resulting script).
QEMU will start, and it will start booting, but nothing graphical will start.
If you switch to the last virtual terminal, you will see

[date] localhost shepherd[1]: Respawning xorg-server.
[date] localhost shepherd[1]: Service host-name has been started.
[date] localhost shepherd[1]: Service xorg-server has been started.
[date] localhost shepherd[1]: Respawning xorg-server.
[date] localhost shepherd[1]: Service host-name has been started.
[date] localhost shepherd[1]: Service xorg-server has been started.
[date] localhost shepherd[1]: Respawning xorg-server.
[date] localhost shepherd[1]: Service host-name has been started.
[date] localhost shepherd[1]: Service xorg-server has been started.
[date] localhost shepherd[1]: Respawning xorg-server.
[date] localhost shepherd[1]: Service host-name has been started.
[date] localhost shepherd[1]: Service xorg-server has been started.
[date] localhost shepherd[1]: Respawning xorg-server.
[date] localhost shepherd[1]: Service host-name has been started.
[date] localhost shepherd[1]: Service xorg-server has been started.
[date] localhost shepherd[1]: Respawning xorg-server.
[date]
localhost shepherd[1]: Service host-name has been started.
[date] localhost shepherd[1]: Service xorg-server has been started.
[date] localhost shepherd[1]:   (Respawning too fast.)

GDM used to work for me with commit 75a3413b4e5c1f7443eb944a36ff364f4c4085f4,
but was broken with e9b87da1c3000c53cf9dbf5e737aa4d6546bd909.  To be bisected?

Greetings,
Maxime.

(xorg-repro.templ is based on the vm-image.tmpl configuration)

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;; This is an operating system configuration for a VM image.
;; Modify it as you see fit and instantiate the changes by running:
;;
;;   guix system reconfigure /etc/config.scm
;;

(use-modules (gnu) (guix) (srfi srfi-1))
(use-service-modules desktop mcron networking spice ssh xorg)
(use-package-modules bootloaders certs fonts nvi
                     package-management wget xorg)

(define vm-image-motd (plain-file "motd" "
\x1b[1;37mThis is the GNU system.  Welcome!\x1b[0m

This instance of Guix is a template for virtualized environments.
You can reconfigure the whole system by adjusting /etc/config.scm
and running:

  guix system reconfigure /etc/config.scm

Run '\x1b[1;37minfo guix\x1b[0m' to browse documentation.

\x1b[1;33mConsider setting a password for the 'root' and 'guest' \
accounts.\x1b[0m
"))

;;; XXX: Xfce does not implement what is needed for the SPICE dynamic
;;; resolution to work (see:
;;; https://gitlab.xfce.org/xfce/xfce4-settings/-/issues/142).  Workaround it
;;; by manually invoking xrandr every second.
#;
(define auto-update-resolution-crutch
  #~(job '(next-second)
         (lambda ()
           (setenv "DISPLAY" ":0.0")
           (setenv "XAUTHORITY" "/home/guest/.Xauthority")
           (execl (string-append #$xrandr "/bin/xrandr") "xrandr" "-s" "0"))
         #:user "guest"))

(operating-system
  (host-name "gnu")
  (timezone "Etc/UTC")
  (locale "en_US.utf8")
  (keyboard-layout (keyboard-layout "us" "altgr-intl"))

  ;; Label for the GRUB boot menu.
  (label (string-append "GNU Guix " (package-version guix)))

  (firmware '())

  ;; Below we assume /dev/vda is the VM's hard disk.
  ;; Adjust as needed.
  (bootloader (bootloader-configuration
               (bootloader grub-bootloader)
               (targets '("/dev/vda"))
               (terminal-outputs '(console))))
  (file-systems (cons (file-system
                        (mount-point "/")
                        (device "/dev/vda1")
                        (type "ext4"))
                      %base-file-systems))

  (users (cons (user-account
                (name "guest")
                (comment "GNU Guix Live")
                (password "")                     ;no password
                (group "users")
                (supplementary-groups '("wheel" "netdev"
                                        "audio" "video")))
               %base-user-accounts))

  ;; Our /etc/sudoers file.  Since 'guest' initially has an empty password,
  ;; allow for password-less sudo.
  (sudoers-file (plain-file "sudoers" "\
root ALL=(ALL) ALL
%wheel ALL=NOPASSWD: ALL\n"))

  (services
   (append (list (service xfce-desktop-service-type)

                 ;; Uncomment the line below to add an SSH server.
                 ;;(service openssh-service-type)

                 ;; Add support for the SPICE protocol, which enables dynamic
                 ;; resizing of the guest screen resolution, clipboard
                 ;; integration with the host, etc.
                 ;;(service spice-vdagent-service-type)

                 ;;(simple-service 'cron-jobs mcron-service-type
                 ;;                (list auto-update-resolution-crutch))

                 ;; Use the DHCP client service rather than NetworkManager.
                 (service dhcp-client-service-type))

           ;; Remove [...], ModemManager, NetworkManager, and wpa-supplicant,
           ;; which don't make sense in a VM.
           (remove (lambda (service)
                     (let ((type (service-kind service)))
                       (or (memq type
                                 (list 
                                       wpa-supplicant-service-type
                                       cups-pk-helper-service-type
                                       network-manager-service-type
                                       modem-manager-service-type))
                           (eq? 'network-manager-applet
                                (service-type-name type)))))
                   (modify-services %desktop-services
                     (login-service-type config =>
                                         (login-configuration
                                          (inherit config)
                                          (motd vm-image-motd)))))))

  ;; Allow resolution of '.local' host names with mDNS.
  #;(name-service-switch %mdns-host-lookup-nss))

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