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+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2014, 2015, 2016, 2017, 2018, 2019 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2016 Alex Kost <alezost@gmail.com>
+;;; Copyright © 2016, 2017, 2018 Chris Marusich <cmmarusich@gmail.com>
+;;; Copyright © 2017 Mathieu Othacehe <m.othacehe@gmail.com>
+;;; Copyright © 2018 Ricardo Wurmus <rekado@elephly.net>
+;;; Copyright © 2019 Christopher Baines <mail@cbaines.net>
+;;; Copyright © 2019 Jakob L. Kreuze <zerodaysfordays@sdf.lonestar.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 scripts system reconfigure)
+  #:autoload   (gnu packages gnupg) (guile-gcrypt)
+  #:use-module (gnu bootloader)
+  #:use-module (gnu services)
+  #:use-module (gnu services herd)
+  #:use-module (gnu services shepherd)
+  #:use-module (gnu system)
+  #:use-module (guix gexp)
+  #:use-module (guix modules)
+  #:use-module (guix monads)
+  #:use-module (guix store)
+  #:use-module (ice-9 match)
+  #:use-module (srfi srfi-1)
+  #:use-module (srfi srfi-11)
+  #:export (switch-system-program
+            switch-to-system
+
+            upgrade-services-program
+            upgrade-shepherd-services
+
+            install-bootloader-program
+            install-bootloader))
+
+;;; Commentary:
+;;;
+;;; This module implements the "effectful" parts of system
+;;; reconfiguration. Although building a system derivation is a pure
+;;; operation, a number of impure operations must be carried out for the
+;;; system configuration to be realized -- chiefly, creation of generation
+;;; symlinks and invocation of activation scripts.
+;;;
+;;; Code:
+
+
+;;;
+;;; Profile creation.
+;;;
+
+(define* (switch-system-program os #:optional profile)
+  "Return an executable store item that, upon being evaluated, will create a
+new generation of PROFILE pointing to the directory of OS, switch to it
+atomically, and run OS's activation script."
+  (program-file
+   "switch-to-system.scm"
+   (with-extensions (list guile-gcrypt)
+     (with-imported-modules (source-module-closure '((guix config)
+                                                     (guix profiles)
+                                                     (guix utils)))
+       #~(begin
+           (use-modules (guix config)
+                        (guix profiles)
+                        (guix utils))
+
+           (define profile
+             (or #$profile (string-append %state-directory "/profiles/system")))
+
+           (let* ((number (1+ (generation-number profile)))
+                  (generation (generation-file-name profile number)))
+             (switch-symlinks generation #$os)
+             (switch-symlinks profile generation)
+             (setenv "GUIX_NEW_SYSTEM" #$os)
+             (primitive-load #$(operating-system-activation-script os))))))))
+
+(define* (switch-to-system eval os #:optional profile)
+  "Using EVAL, a monadic procedure taking a single G-Expression as an argument,
+create a new generation of PROFILE pointing to the directory of OS, switch to
+it atomically, and run OS's activation script."
+  (eval #~(primitive-load #$(switch-system-program os profile))))
+
+
+;;;
+;;; Services.
+;;;
+
+(define (running-services eval)
+  "Using EVAL, a monadic procedure taking a single G-Expression as an argument,
+return the <live-service> objects that are currently running on MACHINE."
+  (define exp
+    (with-imported-modules '((gnu services herd))
+      #~(begin
+          (use-modules (gnu services herd))
+          (let ((services (current-services)))
+            (and services
+                 ;; 'live-service-running' is ignored, as we can't necessarily
+                 ;; serialize arbitrary objects. This should be fine for now,
+                 ;; since 'machine-current-services' is not exposed publicly,
+                 ;; and the resultant <live-service> objects are only used for
+                 ;; resolving service dependencies.
+                 (map (lambda (service)
+                        (list (live-service-provision service)
+                              (live-service-requirement service)))
+                      services))))))
+  (mlet %store-monad ((services (eval exp)))
+    (return (map (match-lambda
+                   ((provision requirement)
+                    (live-service provision requirement #f)))
+                 services))))
+
+;; XXX: Currently, this does NOT attempt to restart running services. See
+;; <https://issues.guix.info/issue/33508> for details.
+(define (upgrade-services-program service-files to-start to-unload to-restart)
+  "Return an executable store item that, upon being evaluated, will upgrade
+the Shepherd (PID 1) by unloading obsolete services and loading new
+services. SERVICE-FILES is a list of Shepherd service files to load, and
+TO-START, TO-UNLOAD, and TO-RESTART are lists of the Shepherd services'
+canonical names (symbols)."
+  (program-file
+   "upgrade-shepherd-services.scm"
+   (with-imported-modules '((gnu services herd))
+    #~(begin
+        (use-modules (gnu services herd)
+                     (srfi srfi-1))
+
+        ;; Load the service files for any new services.
+        (load-services/safe '#$service-files)
+
+        ;; Unload obsolete services and start new services.
+        (for-each unload-service '#$to-unload)
+        (for-each start-service '#$to-start)))))
+
+(define* (upgrade-shepherd-services eval os)
+  "Using EVAL, a monadic procedure taking a single G-Expression as an argument,
+upgrade the Shepherd (PID 1) by unloading obsolete services and loading new
+services as defined by OS."
+  (define target-services
+    (service-value
+     (fold-services (operating-system-services os)
+                    #:target-type shepherd-root-service-type)))
+
+  (mlet* %store-monad ((live-services (running-services eval)))
+    (let*-values (((to-unload to-restart)
+                   (shepherd-service-upgrade live-services target-services)))
+      (let* ((to-unload (map live-service-canonical-name to-unload))
+             (to-restart (map shepherd-service-canonical-name to-restart))
+             (to-start (lset-difference eqv?
+                                        (map shepherd-service-canonical-name
+                                             target-services)
+                                        (map live-service-canonical-name
+                                             live-services)))
+             (service-files (map shepherd-service-file target-services)))
+        (eval #~(primitive-load #$(upgrade-services-program service-files
+                                                            to-start
+                                                            to-unload
+                                                            to-restart)))))))
+
+
+;;;
+;;; Bootloader configuration.
+;;;
+
+(define (install-bootloader-program installer bootloader-package bootcfg
+                                    bootcfg-file device target)
+  "Return an executable store item that, upon being evaluated, will install
+BOOTCFG to BOOTCFG-FILE, a target file name, on DEVICE, a file system device,
+at TARGET, a mount point, and subsequently run INSTALLER from
+BOOTLOADER-PACKAGE."
+  (program-file
+   "install-bootloader.scm"
+   (with-extensions (list guile-gcrypt)
+     (with-imported-modules (source-module-closure '((gnu build bootloader)
+                                                     (gnu build install)
+                                                     (guix store)
+                                                     (guix utils)))
+       #~(begin
+           (use-modules (gnu build bootloader)
+                        (gnu build install)
+                        (guix build utils)
+                        (guix store)
+                        (guix utils)
+                        (ice-9 binary-ports)
+                        (srfi srfi-34)
+                        (srfi srfi-35))
+           (let* ((gc-root (string-append #$target %gc-roots-directory "/bootcfg"))
+                  (temp-gc-root (string-append gc-root ".new")))
+             (switch-symlinks temp-gc-root gc-root)
+             (install-boot-config #$bootcfg #$bootcfg-file #$target)
+             ;; Preserve the previous activation's garbage collector root
+             ;; until the bootloader installer has run, so that a failure in
+             ;; the bootloader's installer script doesn't leave the user with
+             ;; a broken installation.
+             (when #$installer
+               (catch #t
+                 (lambda ()
+                   (#$installer #$bootloader-package #$device #$target))
+                 (lambda args
+                   (delete-file temp-gc-root)
+                   (apply throw args))))
+             (rename-file temp-gc-root gc-root)))))))
+
+(define* (install-bootloader eval configuration bootcfg
+                             #:key
+                             (run-installer? #t)
+                             (target "/"))
+  "Using EVAL, a monadic procedure taking a single G-Expression as an argument,
+configure the bootloader on TARGET such that OS will be booted by default and
+additional configurations specified by MENU-ENTRIES can be selected."
+  (let* ((bootloader (bootloader-configuration-bootloader configuration))
+         (installer (and run-installer?
+                         (bootloader-installer bootloader)))
+         (package (bootloader-package bootloader))
+         (device (bootloader-configuration-target configuration))
+         (bootcfg-file (bootloader-configuration-file bootloader)))
+    (eval #~(primitive-load #$(install-bootloader-program installer
+                                                          package
+                                                          bootcfg
+                                                          bootcfg-file
+                                                          device
+                                                          target)))))