system: images: Add wsl2 module.

* gnu/system/images/wsl2.scm: New file.
* gnu/local.mk (GNU_SYSTEM_MODULES): Add it.
* doc/guix.texi ("System Images"): Document it.

Signed-off-by: Mathieu Othacehe <othacehe@gnu.org>

3 files changed, 185 insertions, 0 deletions

diff --git a/doc/guix.texi b/doc/guix.texi
index 6c44c22a32..ba13ebf144 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -41476,6 +41476,8 @@ one or multiple partitions.
 
 @item @code{tarball}, a tar.gz image archive.
 
+@item @code{wsl2}, a WSL2 image.
+
 @end itemize
 
 @item @code{platform} (default: @code{#false})
@@ -41842,6 +41844,17 @@ Build an image similar to the one built by the @code{hurd-image-type}
 but with the @code{format} set to @code{'compressed-qcow2}.
 @end defvr
 
+@defvr {Scheme Variable} wsl2-image-type
+Build an image for the @acronym{WSL2, Windows Subsystem for Linux 2}.
+It can be imported by running:
+
+@example
+wsl --import Guix ./guix ./wsl2-image.tar.gz
+wsl -d Guix
+@end example
+
+@end defvr
+
 So, if we get back to the @code{guix system image} command taking an
 @code{operating-system} declaration as argument.  By default, the
 @code{efi-raw-image-type} is used to turn the provided
diff --git a/gnu/local.mk b/gnu/local.mk
index 4774be2688..4e982dc6e3 100644
--- a/gnu/local.mk
+++ b/gnu/local.mk
@@ -53,6 +53,7 @@
 # Copyright © 2022 John Kehayias <john.kehayias@protonmail.com>
 # Copyright © 2022 muradm <mail@muradm.net>
 # Copyright © 2022 Hilton Chain <hako@ultrarare.space>
+# Copyright © 2022 Alex Griffin <a@ajgrf.com>
 #
 # This file is part of GNU Guix.
 #
@@ -718,6 +719,7 @@ GNU_SYSTEM_MODULES =				\
   %D%/system/images/pine64.scm			\
   %D%/system/images/pinebook-pro.scm		\
   %D%/system/images/rock64.scm			\
+  %D%/system/images/wsl2.scm			\
 						\
   %D%/machine.scm				\
 						\
diff --git a/gnu/system/images/wsl2.scm b/gnu/system/images/wsl2.scm
new file mode 100644
index 0000000000..15cb4f69b8
--- /dev/null
+++ b/gnu/system/images/wsl2.scm
@@ -0,0 +1,170 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2022 Alex Griffin <a@ajgrf.com>
+;;; Copyright © 2022 Mathieu Othacehe <othacehe@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 (gnu system images wsl2)
+  #:use-module (gnu bootloader)
+  #:use-module (gnu image)
+  #:use-module (gnu packages admin)
+  #:use-module (gnu packages base)
+  #:use-module (gnu packages bash)
+  #:use-module (gnu packages guile)
+  #:use-module (gnu packages linux)
+  #:use-module (gnu services)
+  #:use-module (gnu services base)
+  #:use-module (gnu system)
+  #:use-module (gnu system image)
+  #:use-module (gnu system shadow)
+  #:use-module (guix build-system trivial)
+  #:use-module (guix gexp)
+  #:use-module (guix packages)
+  #:export (wsl-boot-program
+            wsl-os
+            wsl2-image))
+
+(define (wsl-boot-program user)
+  "Program that runs the system boot script, then starts a login shell as
+USER."
+  (program-file
+   "wsl-boot-program"
+   (with-imported-modules '((guix build syscalls))
+     #~(begin
+         (use-modules (guix build syscalls))
+         (unless (file-exists? "/run/current-system")
+           (let ((shepherd-socket "/var/run/shepherd/socket"))
+             ;; Clean up this file so we can wait for it later.
+             (when (file-exists? shepherd-socket)
+               (delete-file shepherd-socket))
+
+             ;; Child process boots the system and is replaced by shepherd.
+             (when (zero? (primitive-fork))
+               (let* ((system-generation
+                       (readlink "/var/guix/profiles/system"))
+                      (system (readlink
+                               (string-append
+                                (if (absolute-file-name? system-generation)
+                                    ""
+                                    "/var/guix/profiles/")
+                                system-generation))))
+                 (setenv "GUIX_NEW_SYSTEM" system)
+                 (execl #$(file-append guile-3.0 "/bin/guile")
+                        "guile"
+                        "--no-auto-compile"
+                        (string-append system "/boot"))))
+
+             ;; Parent process waits for shepherd before continuing.
+             (while (not (file-exists? shepherd-socket))
+               (sleep 1))))
+
+         (let* ((pw (getpw #$user))
+                (shell (passwd:shell pw))
+                (sudo #+(file-append sudo "/bin/sudo"))
+                (args (cdr (command-line))))
+           ;; Save the value of $PATH set by WSL.  Useful for finding
+           ;; Windows binaries to run with WSL's binfmt interop.
+           (setenv "WSLPATH" (getenv "PATH"))
+
+           ;; /run is mounted with the nosuid flag by WSL.  This prevents
+           ;; running the /run/setuid-programs.  Remount it without this flag
+           ;; as a workaround.  See:
+           ;; https://github.com/microsoft/WSL/issues/8716.
+           (mount #f "/run" #f
+                  MS_REMOUNT
+                  #:update-mtab? #f)
+
+           ;; Start login shell as user.
+           (apply execl sudo "sudo"
+                  "--preserve-env=WSLPATH"
+                  "-u" #$user
+                  "--"
+                  shell "-l" args))))))
+
+(define dummy-package
+  (package
+    (name "dummy")
+    (version "0")
+    (source #f)
+    (build-system trivial-build-system)
+    (arguments
+     `(#:modules ((guix build utils))
+       #:target #f
+       #:builder (begin
+                   (use-modules (guix build utils))
+                   (let* ((out (assoc-ref %outputs "out"))
+                          (dummy (string-append out "/dummy")))
+                     (mkdir-p out)
+                     (call-with-output-file dummy
+                       (const #t))))))
+    (home-page #f)
+    (synopsis #f)
+    (description #f)
+    (license #f)))
+
+(define dummy-bootloader
+  (bootloader
+   (name 'dummy-bootloader)
+   (package dummy-package)
+   (configuration-file "/dev/null")
+   (configuration-file-generator
+    (lambda (. _rest)
+      (plain-file "dummy-bootloader" "")))
+   (installer #~(const #t))))
+
+(define dummy-kernel dummy-package)
+
+(define (dummy-initrd . _rest)
+  (plain-file "dummy-initrd" ""))
+
+(define-public wsl-os
+  (operating-system
+    (host-name "gnu")
+    (timezone "Etc/UTC")
+    (bootloader
+     (bootloader-configuration
+      (bootloader dummy-bootloader)))
+    (kernel dummy-kernel)
+    (initrd dummy-initrd)
+    (initrd-modules '())
+    (firmware '())
+    (file-systems '())
+    (users (cons* (user-account
+                   (name "guest")
+                   (group "users")
+                   (supplementary-groups '("wheel")) ; allow use of sudo
+                   (password "")
+                   (comment "Guest of GNU"))
+                  (user-account
+                   (inherit %root-account)
+                   (shell (wsl-boot-program "guest")))
+                  %base-user-accounts))
+    (services
+     (list
+      (service guix-service-type)
+      (service special-files-service-type
+               `(("/bin/sh" ,(file-append bash "/bin/bash"))
+                 ("/bin/mount" ,(file-append util-linux "/bin/mount"))
+                 ("/usr/bin/env" ,(file-append coreutils "/bin/env"))))))))
+
+(define wsl2-image
+  (image
+   (inherit
+    (os->image wsl-os
+               #:type wsl2-image-type))
+   (name 'wsl2-image)))
+
+wsl2-image