services: slim: Allow SLiM to be started on multiple ttys.

This change makes it possible to add multiple SLiM services to an operating
system configuration by setting the new 'display' and 'vt' fields in their
configurations to different values.  Each SLiM service will get its own
authfile, logfile, lockfile, and shepherd service, which will start SLiM on a
different tty.

* gnu/services/xorg.scm: Export slim-configuration-display and
  slim-configuration-vt.
  (<slim-configuration>)[display, vt]: New fields.
  (slim-shepherd-service): Refactor let.
  [slim.cfg]: Use new fields for setting display_name, xserver_arguments,
  authfile, lockfile, and logfile.
  [shepherd-service][provision]: Name the shepherd service according to the
  value of 'vt'.
  [shepherd-service][start]: Delete the right lockfile.

Signed-off-by: Ludovic Courtès <ludo@gnu.org>

gnu/services/xorg.scm

@@ -83,6 +83,8 @@
             slim-configuration-shepherd
             slim-configuration-auto-login-session
             slim-configuration-xorg
+            slim-configuration-display
+            slim-configuration-vt
             slim-configuration-sessreg
 
             slim-service-type
@@ -488,6 +490,10 @@ desktop session from the system or user profile will be used."
                       (default #f))
   (xorg-configuration slim-configuration-xorg
                       (default (xorg-configuration)))
+  (display slim-configuration-display
+           (default ":0"))
+  (vt slim-configuration-vt
+      (default "vt7"))
   (sessreg slim-configuration-sessreg
            (default sessreg)))
 
@@ -499,20 +505,26 @@ desktop session from the system or user profile will be used."
          (slim-configuration-allow-empty-passwords? config))))
 
 (define (slim-shepherd-service config)
-  (define slim.cfg
-    (let ((xinitrc (xinitrc #:fallback-session
-                            (slim-configuration-auto-login-session config)))
-          (xauth   (slim-configuration-xauth config))
-          (startx  (xorg-start-command (slim-configuration-xorg config)))
-          (shepherd   (slim-configuration-shepherd config))
-          (theme-name (slim-configuration-theme-name config))
-          (sessreg (slim-configuration-sessreg config)))
+  (let* ((xinitrc (xinitrc #:fallback-session
+                           (slim-configuration-auto-login-session config)))
+         (xauth   (slim-configuration-xauth config))
+         (startx  (xorg-start-command (slim-configuration-xorg config)))
+         (display (slim-configuration-display config))
+         (vt (slim-configuration-vt config))
+         (shepherd   (slim-configuration-shepherd config))
+         (theme-name (slim-configuration-theme-name config))
+         (sessreg (slim-configuration-sessreg config))
+         (lockfile (string-append "/var/run/slim-" vt ".lock")))
+    (define slim.cfg
       (mixed-text-file "slim.cfg"  "
 default_path /run/current-system/profile/bin
 default_xserver " startx "
-xserver_arguments :0 vt7
+display_name " display "
+xserver_arguments " vt "
 xauth_path " xauth "/bin/xauth
-authfile /var/run/slim.auth
+authfile /var/run/slim-" vt ".auth
+lockfile " lockfile "
+logfile /var/log/slim-" vt ".log
 
 # The login command.  '%session' is replaced by the chosen session name, one
 # of the names specified in the 'sessions' setting: 'wmaker', 'xfce', etc.
@@ -530,32 +542,33 @@ reboot_cmd " shepherd "/sbin/reboot\n"
     "")
 (if theme-name
     (string-append "current_theme " theme-name "\n")
-    ""))))
+    "")))
 
-  (define theme
-    (slim-configuration-theme config))
+    (define theme
+      (slim-configuration-theme config))
 
-  (list (shepherd-service
-         (documentation "Xorg display server")
-         (provision '(xorg-server))
-         (requirement '(user-processes host-name udev))
-         (start
-          #~(lambda ()
-              ;; A stale lock file can prevent SLiM from starting, so remove it to
-              ;; be on the safe side.
-              (false-if-exception (delete-file "/var/run/slim.lock"))
+    (list (shepherd-service
+           (documentation "Xorg display server")
+           (provision (list (symbol-append 'xorg-server-
+                                           (string->symbol vt))))
+           (requirement '(user-processes host-name udev))
+           (start
+            #~(lambda ()
+                ;; A stale lock file can prevent SLiM from starting, so remove it to
+                ;; be on the safe side.
+                (false-if-exception (delete-file lockfile))
 
-              (fork+exec-command
-               (list (string-append #$(slim-configuration-slim config)
-                                    "/bin/slim")
-                     "-nodaemon")
-               #:environment-variables
-               (list (string-append "SLIM_CFGFILE=" #$slim.cfg)
-                     #$@(if theme
-                            (list #~(string-append "SLIM_THEMESDIR=" #$theme))
-                            #~())))))
-         (stop #~(make-kill-destructor))
-         (respawn? #t))))
+                (fork+exec-command
+                 (list (string-append #$(slim-configuration-slim config)
+                                      "/bin/slim")
+                       "-nodaemon")
+                 #:environment-variables
+                 (list (string-append "SLIM_CFGFILE=" #$slim.cfg)
+                       #$@(if theme
+                              (list #~(string-append "SLIM_THEMESDIR=" #$theme))
+                              #~())))))
+           (stop #~(make-kill-destructor))
+           (respawn? #t)))))
 
 (define slim-service-type
   (service-type (name 'slim)