[bug#68289] [PATCH] services: xorg: Add xorg-start-command-xinit procedure.

[Tomas Volf <~@wolfsden.cz>]

When user does not use any desktop environment, the typical sequence is to log
in and then type `startx' into the tty to get a window manager running.  Most
distributions do provide startx by default, but Guix has only
xorg-start-command, that is not suitable for this type of task.

This commit adds second procedure, xorg-start-command-xinit, that correctly
picks virtual terminal to use, sets up XAUTHORITY and starts xinit with
correct arguments.  That should make running Guix without any desktop
environment more approachable.

* gnu/services/xorg.scm (xorg-start-command-xinit): New procedure.
(define-module): Export it.
* doc/guix.texi (X Window): Document it.

Change-Id: I17cb16093d16a5c6550b1766754700d4fe014ae9
---
 doc/guix.texi         | 18 ++++++++++
 gnu/services/xorg.scm | 82 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 100 insertions(+)

diff --git a/doc/guix.texi b/doc/guix.texi
index a648a106b3..72c5527270 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -23177,6 +23177,24 @@ X Window
 Usually the X server is started by a login manager.
 @end deffn
 
+@deffn {Procedure} xorg-start-command-xinit [config]
+Return a @code{startx} script in which the modules, fonts,
+etc. specified in @var{config}, are available.  The result should be
+used in place of @code{startx}.  Compared to the
+@code{xorg-start-command} it calls xinit, therefore it works well when
+executed from tty.  If you are using a desktop environment, you are
+unlikely to have a need for this procedure.
+
+The resulting file should be invoked by user from the tty after login,
+common name for the program would be @code{startx}.  Convenience link
+can be created by (for example) this home service:
+
+@lisp
+(simple-service 'home-files home-files-service-type
+                `(("bin/startx" ,(xorg-start-command-xinit))))
+@end lisp
+@end deffn
+
 
 @defvar screen-locker-service-type
 Type for a service that adds a package for a screen locker or screen
diff --git a/gnu/services/xorg.scm b/gnu/services/xorg.scm
index 1ee15ea90c..2f5aa3b4f3 100644
--- a/gnu/services/xorg.scm
+++ b/gnu/services/xorg.scm
@@ -53,6 +53,7 @@ (define-module (gnu services xorg)
   #:use-module (gnu packages gnome)
   #:use-module (gnu packages admin)
   #:use-module (gnu packages bash)
+  #:use-module (gnu packages linux)
   #:use-module (gnu system shadow)
   #:use-module (guix build-system glib-or-gtk)
   #:use-module (guix build-system trivial)
@@ -84,6 +85,7 @@ (define-module (gnu services xorg)
 
             xorg-wrapper
             xorg-start-command
+            xorg-start-command-xinit
             xinitrc
             xorg-server-service-type
 
@@ -414,6 +416,86 @@ (define* (xorg-start-command #:optional (config (xorg-configuration)))
 
   (program-file "startx" exp))
 
+(define* (xorg-start-command-xinit #:optional (config (xorg-configuration)))
+  "Return a @code{startx} script in which the modules, fonts, etc. specified in
+@var{config}, are available.  The result should be used in place of
+@code{startx}.  Compared to the @code{xorg-start-command} it calls xinit,
+therefore it works well when executed from tty."
+  (define X
+    (xorg-wrapper config))
+
+  (define exp
+    ;; Small wrapper providing subset of functionality of typical startx script
+    ;; from distributions like alpine.
+    #~(begin
+        (use-modules (ice-9 popen)
+                     (ice-9 textual-ports))
+
+        (define (checked-system* . args)
+          (if (= 0 (status:exit-val (apply system* args)))
+              #t
+              (error "command failed")))
+
+        (define (capture-stdout . prog+args)
+          (let* ((port (apply open-pipe* OPEN_READ prog+args))
+                 (data (get-string-all port)))
+            (if (= 0 (status:exit-val (close-pipe port)))
+                (string-trim-right data #\newline)
+                (error "command failed"))))
+
+        (define (determine-unused-display n)
+          (let ((lock-file (format #f "/tmp/.X~a-lock" n))
+                (sock-file (format #f "/tmp/.X11-unix/X~a" n)))
+            (if (or (file-exists? lock-file)
+                    (false-if-exception
+                     (eq? 'socket (stat:type (stat sock-file)))))
+                (determine-unused-display (+ n 1))
+                (format #f ":~a" n))))
+        (define (determine-vty)
+          (let ((fd0 (readlink "/proc/self/fd/0"))
+                (pref "/dev/tty"))
+            (if (string-prefix? pref fd0)
+                (string-append "vt" (substring fd0 (string-length pref)))
+                (error (format #f "Cannot determine VT from: ~a" fd0)))))
+
+        (define (enable-xauth server-auth-file display)
+          ;; Configure and enable X authority
+          (or (getenv "XAUTHORITY")
+              (setenv "XAUTHORITY" (string-append (getenv "HOME") "/.Xauthority")))
+
+          (let* ((bin/xauth (string-append #$xauth "/bin/xauth"))
+                 (bin/mcookie (string-append #$util-linux "/bin/mcookie"))
+
+                 (mcookie (capture-stdout bin/mcookie)))
+            (checked-system* bin/xauth "-qf" server-auth-file
+                             "add" display "." mcookie)
+            (checked-system* bin/xauth "-q"
+                             "add" display "." mcookie)))
+
+        (let* ((xinit (string-append #$xinit "/bin/xinit"))
+               (display (determine-unused-display 0))
+               (vty (determine-vty))
+               (server-auth-port (mkstemp "/tmp/serverauth.XXXXXX"))
+               (server-auth-file (port-filename server-auth-port)))
+          (close-port server-auth-port)
+          (enable-xauth server-auth-file display)
+          (apply execl
+                 xinit
+                 xinit
+                 "--"
+                 #$X
+                 display
+                 vty
+                 "-keeptty"
+                 "-auth" server-auth-file
+                 ;; These are set by xorg-start-command, so do the same to keep
+                 ;; it consistent.
+                 "-logverbose" "-verbose" "-terminate"
+                 #$@(xorg-configuration-server-arguments config)
+                 (cdr (command-line))))))
+
+  (program-file "startx" exp))
+
 (define* (xinitrc #:key fallback-session)
   "Return a system-wide xinitrc script that starts the specified X session,
 which should be passed to this script as the first argument.  If not, the

base-commit: e994bc0abf39db228fa61f1aaf24840c19c47647
-- 
2.41.0