system: Make /run/current-system at activation time.

* gnu/system.scm (etc-directory): Change default value of #:profile.
  Change contents of SHELLS.  Use /run/current-system/profile/{s,}bin in
  BASHRC.
  (operating-system-boot-script)[%modules]: Add (guix build
  linux-initrd).  Add call to 'activate-current-system' in gexp.
  (operating-system-initrd-file, operating-system-grub.cfg): New
  procedures.
  (operating-system-derivation): Don't build grub.cfg here and remove it
  from the file union.
* gnu/system/vm.scm (qemu-image): Remove #:populate.
  (operating-system-build-gid, operating-system-default-contents):
  Remove.
  (system-qemu-image): Remove call to
  'operating-system-default-contents'.  Use 'operating-system-grub.cfg'
  to get grub.cfg.  Add GRUB.CFG to #:inputs.
  (system-qemu-image/shared-store): Likewise, but don't add GRUB.CFG to
  #:inputs.
  (system-qemu-image/shared-store-script): Pass --system kernel option.
* guix/build/activation.scm (%booted-system, %current-system): New
  variables.
  (boot-time-system, activate-current-system): New procedures.
* guix/build/install.scm (evaluate-populate-directive): Add case
  for ('directory name uid gid mode).
  (directives, populate-root-file-system): New procedures.
* guix/build/vm.scm (initialize-hard-disk): Replace calls to
  'evaluate-populate-directive' by a call to
  'populate-root-file-system'.
* gnu/services/dmd.scm (dmd-configuration-file): Use
  /run/current-system/profile/bin.
* gnu/services/xorg.scm (slim-service): Likewise.

1 files changed, 32 insertions, 1 deletions

diff --git a/guix/build/activation.scm b/guix/build/activation.scm
index 267c592b52..49f98c021d 100644
--- a/guix/build/activation.scm
+++ b/guix/build/activation.scm
@@ -18,13 +18,15 @@
 
 (define-module (guix build activation)
   #:use-module (guix build utils)
+  #:use-module (guix build linux-initrd)
   #:use-module (ice-9 ftw)
   #:use-module (ice-9 match)
   #:use-module (srfi srfi-1)
   #:use-module (srfi srfi-26)
   #:export (activate-users+groups
             activate-etc
-            activate-setuid-programs))
+            activate-setuid-programs
+            activate-current-system))
 
 ;;; Commentary:
 ;;;
@@ -195,4 +197,33 @@ numeric gid or #f."
 
   (for-each make-setuid-program programs))
 
+(define %booted-system
+  ;; The system we booted in (a symlink.)
+  "/run/booted-system")
+
+(define %current-system
+  ;; The system that is current (a symlink.)  This is not necessarily the same
+  ;; as %BOOTED-SYSTEM, for instance because we can re-build a new system
+  ;; configuration and activate it, without rebooting.
+  "/run/current-system")
+
+(define (boot-time-system)
+  "Return the '--system' argument passed on the kernel command line."
+  (find-long-option "--system" (linux-command-line)))
+
+(define* (activate-current-system #:optional (system (boot-time-system))
+                                  #:key boot?)
+  "Atomically make SYSTEM the current system.  When BOOT? is true, also make
+it the booted system."
+  (format #t "making '~a' the current system...~%" system)
+  (when boot?
+    (when (file-exists? %booted-system)
+      (delete-file %booted-system))
+    (symlink system %booted-system))
+
+  ;; Atomically make SYSTEM current.
+  (let ((new (string-append %current-system ".new")))
+    (symlink system new)
+    (rename-file new %current-system)))
+
 ;;; activation.scm ends here