system: Add (guix build activation).

* gnu/services/dmd.scm (dmd-configuration-file): Remove 'etc'
  parameter.  Move /etc activation code to...
* guix/build/activation.scm: ... here; new file.
* gnu/system.scm (operating-system-boot-script): Augment script: add
  (guix build activation) to the load path; call 'activate-etc'.
* Makefile.am (MODULES): Add guix/build/activation.scm.

Makefile.am

@@ -71,6 +71,7 @@ MODULES =					\
   guix/build/rpath.scm				\
   guix/build/svn.scm				\
   guix/build/vm.scm				\
+  guix/build/activation.scm			\
   guix/packages.scm				\
   guix/snix.scm					\
   guix/scripts/download.scm			\

gnu/services/dmd.scm

@@ -30,9 +30,8 @@
 ;;;
 ;;; Code:
 
-(define (dmd-configuration-file services etc)
+(define (dmd-configuration-file services)
-  "Return the dmd configuration file for SERVICES, that initializes /etc from
+  "Return the dmd configuration file for SERVICES."
-ETC (the derivation that builds the /etc directory) on startup."
   (define config
     #~(begin
         (use-modules (ice-9 ftw))
@@ -48,28 +47,6 @@ ETC (the derivation that builds the /etc directory) on startup."
                        #:stop #$(service-stop service)))
                  services))
 
-        ;; /etc is a mixture of static and dynamic settings.  Here is where we
-        ;; initialize it from the static part.
-        (format #t "populating /etc from ~a...~%" #$etc)
-        (let ((rm-f (lambda (f)
-                      (false-if-exception (delete-file f)))))
-          (rm-f "/etc/static")
-          (symlink #$etc "/etc/static")
-          (for-each (lambda (file)
-                      ;; TODO: Handle 'shadow' specially so that changed
-                      ;; password aren't lost.
-                      (let ((target (string-append "/etc/" file))
-                            (source (string-append "/etc/static/" file)))
-                        (rm-f target)
-                        (symlink source target)))
-                    (scandir #$etc
-                             (lambda (file)
-                               (not (member file '("." ".."))))))
-
-          ;; Prevent ETC from being GC'd.
-          (rm-f "/var/guix/gcroots/etc-directory")
-          (symlink #$etc "/var/guix/gcroots/etc-directory"))
-
         ;; guix-daemon 0.6 aborts if 'PATH' is undefined, so work around it.
         (setenv "PATH" "/run/current-system/bin")
 

gnu/system.scm

@@ -256,10 +256,25 @@ we're running in the final root."
   (mlet* %store-monad
       ((services (sequence %store-monad (operating-system-services os)))
        (etc      (operating-system-etc-directory os))
-       (dmd-conf (dmd-configuration-file services etc)))
+       (modules  (imported-modules '((guix build activation))))
+       (compiled (compiled-modules '((guix build activation))))
+       (dmd-conf (dmd-configuration-file services)))
     (gexp->file "boot"
-                #~(execl (string-append #$dmd "/bin/dmd")
+                #~(begin
-                         "dmd" "--config" #$dmd-conf))))
+                    (eval-when (expand load eval)
+                      ;; Make sure 'use-modules' below succeeds.
+                      (set! %load-path (cons #$modules %load-path))
+                      (set! %load-compiled-path
+                            (cons #$compiled %load-compiled-path)))
+
+                    (use-modules (guix build activation))
+
+                    ;; Populate /etc.
+                    (activate-etc #$etc)
+
+                    ;; Start dmd.
+                    (execl (string-append #$dmd "/bin/dmd")
+                           "dmd" "--config" #$dmd-conf)))))
 
 (define (operating-system-derivation os)
   "Return a derivation that builds OS."

guix/build/activation.scm

@@ -0,0 +1,63 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2013, 2014 Ludovic Courtès <ludo@gnu.org>
+;;;
+;;; This file is part of GNU Guix.
+;;;
+;;; GNU Guix is free software; you can redistribute it and/or modify it
+;;; under the terms of the GNU General Public License as published by
+;;; the Free Software Foundation; either version 3 of the License, or (at
+;;; your option) any later version.
+;;;
+;;; GNU Guix is distributed in the hope that it will be useful, but
+;;; WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;;; GNU General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU General Public License
+;;; along with GNU Guix.  If not, see <http://www.gnu.org/licenses/>.
+
+(define-module (guix build activation)
+  #:use-module (ice-9 ftw)
+  #:export (activate-etc))
+
+;;; Commentary:
+;;;
+;;; This module provides "activation" helpers.  Activation is the process that
+;;; consists in setting up system-wide files and directories so that an
+;;; 'operating-system' configuration becomes active.
+;;;
+;;; Code:
+
+(define (activate-etc etc)
+  "Install ETC, a directory in the store, as the source of static files for
+/etc."
+
+  ;; /etc is a mixture of static and dynamic settings.  Here is where we
+  ;; initialize it from the static part.
+
+  (format #t "populating /etc from ~a...~%" etc)
+  (let ((rm-f (lambda (f)
+                (false-if-exception (delete-file f)))))
+    (rm-f "/etc/static")
+    (symlink etc "/etc/static")
+    (for-each (lambda (file)
+                ;; TODO: Handle 'shadow' specially so that changed
+                ;; password aren't lost.
+                (let ((target (string-append "/etc/" file))
+                      (source (string-append "/etc/static/" file)))
+                  (rm-f target)
+                  (symlink source target)))
+              (scandir etc
+                       (lambda (file)
+                         (not (member file '("." ".."))))
+
+                       ;; The default is 'string-locale<?', but we don't have
+                       ;; it when run from the initrd's statically-linked
+                       ;; Guile.
+                       string<?))
+
+    ;; Prevent ETC from being GC'd.
+    (rm-f "/var/guix/gcroots/etc-directory")
+    (symlink etc "/var/guix/gcroots/etc-directory")))
+
+;;; activation.scm ends here