diff --git a/gnu/bootloader/grub.scm b/gnu/bootloader/grub.scm
index 6e71f30f0d..b57c78e156 100644
--- a/gnu/bootloader/grub.scm
+++ b/gnu/bootloader/grub.scm
@@ -34,6 +34,7 @@ (define-module (gnu bootloader grub)
   #:use-module (gnu packages bootloaders)
   #:autoload   (gnu packages gtk) (guile-cairo guile-rsvg)
   #:autoload   (gnu packages xorg) (xkeyboard-config)
+  #:use-module (gnu services configuration)
   #:use-module (gnu system boot)
   #:use-module (gnu system file-systems)
   #:use-module (gnu system keyboard)
@@ -83,6 +84,13 @@ (define (sanitize str)
       (list->string (fold-right glycerin '()
                                 (map isopropyl (string->list #$str))))))
 
+;; Name of variable with GRUB search result for boot device.
+(define %boot "boot")
+
+;; TODO: Use device-mount-point and device-subvol.
+(define (normalize-file file)
+  #~(string-append "($" #$%boot ")" #$(sanitize file)))
+
 (define* (search/target type targets var #:optional (port #f))
   "Returns a gexp of a GRUB search command for target TYPE, storing the
 result in VAR.  Optionally outputs to the gexp PORT instead of returning
@@ -97,43 +105,6 @@ (define (form name val)
            (label (form "fs_label" label))
            (else (form "file" (sanitize path)))))))
 
-(define* (search/menu-entry device file var #:optional (port #f))
-  "Return the GRUB 'search' command to look for DEVICE, which contains
-FILE, a gexp.  The result is a gexp that can be inserted in the
-grub.cfg-generation code to set the variable VAR.  This procedure is
-able to handle DEVICEs unmounted at evaltime."
-  (match device
-    ;; Preferably refer to DEVICE by its UUID or label.  This is more
-    ;; efficient and less ambiguous, see <http://bugs.gnu.org/22281>.
-    ((? uuid? idfk) ; calling idfk uuid here errors for some reason
-     #~(format #$port "search.fs_uuid ~a ~a~%" #$(uuid->string device) #$var))
-    ((? file-system-label? label)
-     #~(format #$port "search.fs_label \"~a\" ~a~%"
-               #$(sanitize (file-system-label->string label)) #$var))
-    ((? (lambda (device)
-          (and (string? device) (string-contains device ":/"))) nfs-uri)
-     ;; If the device is an NFS share, then we assume that the expected
-     ;; file on that device (e.g. the GRUB background image or the kernel)
-     ;; has to be loaded over the network.  Otherwise we would need an
-     ;; additional device information for some local disk to look for that
-     ;; file, which we do not have.
-     ;;
-     ;; TFTP is preferred to HTTP because it is used more widely and
-     ;; specified in standards more widely--especially BOOTP/DHCPv4
-     ;; defines a TFTP server for DHCP option 66, but not HTTP.
-     ;;
-     ;; Note: DHCPv6 specifies option 59 to contain a boot-file-url,
-     ;; which can contain a HTTP or TFTP URL.
-     ;;
-     ;; Note: It is assumed that the file paths are of a similar
-     ;; setup on both the TFTP server and the NFS server (it is
-     ;; not possible to search for files on TFTP).
-     ;;
-     ;; TODO: Allow HTTP.
-     #~(format #$port "set ~a=tftp~%" #$var))
-    ((or #f (? string?))
-     #~(format #$port "search.file \"~a\" ~a~%" #$(sanitize file) #$var))))
-
 (define (when-list . xs) (filter identity xs))
 
 
@@ -173,6 +144,24 @@ (define (grub-theme-png theme)
                                   #:height #$height)))))))
       (_ image))))
 
+(define (serialize-grub-theme value install)
+  (match-record value <grub-theme>
+    (image color-normal color-highlight)
+    (define (colors->str colors)
+      (format #f "~a/~a" (assoc-ref colors 'fg) (assoc-ref colors 'bg)))
+    (and image
+         #~(format #f "insmod png
+if background_image \"($root)~a/image.png\"; then
+  set color_normal=~a
+  set color_highlight=~a
+else
+  set menu_color_normal=cyan/blue
+  set menu_color_highlight=white/blue
+fi~%"
+                   #$(sanitize install)
+                   #$(colors->str color-normal)
+                   #$(colors->str color-highlight)))))
+
 
 ;;;
 ;;; Core config.
@@ -288,140 +277,263 @@ (define* (core.img grub format #:key bootloader-config store-crypto-devices
 ;;; This is what does the heavy lifting after core.img finds it.
 ;;;
 
-;; TODO: use define-configuration.
-(define (menu-entry->gexp entry extra-initrd port)
-  (match-menu-entry
-    entry
-    (label device linux linux-arguments initrd multiboot-kernel
-     multiboot-arguments multiboot-modules chain-loader)
-    (let ((normalize-file
-            (compose sanitize (cut normalize-file entry <>))))
-      #~(begin
-          (format #$port "menuentry ~s {~%  " #$label)
-          #$(search/menu-entry
-              device (or linux multiboot-kernel chain-loader) "boot" port)
-          #$@(cond
-               (linux
-                 (list #~(format
-                           #$port "  linux \"($boot)~a\" ~a~%"
-                           #$(normalize-file linux)
-                           ;; GRUB passes rest of the line _verbatim_.
-                           (string-join (list #$@linux-arguments)))
-                       #~(format #$port "  initrd ~a \"($boot)~a\"~%"
-                                 (if #$extra-initrd
-                                     (string-append "($boot)\""
-                                                    (normalize-file
-                                                      #$extra-initrd)
-                                                    "\"")
-                                     "")
-                                 #$(normalize-file initrd))))
-               ;; Previously, this provided a (wrong) root= argument.
-               ;; Just don't bother anymore; better less info than
-               ;; wrong info.
-               (multiboot-kernel
-                 (cons
-                   #~(format #$port "  multiboot \"($boot)~a\" ~a~%"
-                             #$(normalize-file multiboot-kernel)
-                             (string-join (list #$@multiboot-arguments)))
-                   (map (lambda (mod)
-                          #~(format port "  module \"($boot)~a\"~%"
-                                    #$(normalize-file mod)))
-                        multiboot-modules)))
-               (chain-loader
-                 (list #~(format #$port "  chainloader \"~a\"~%"
-                                 #$(normalize-file chain-loader)))))
-          (format #$port "}~%")))))
+(define (serialize-string value)
+  (match value
+    ((key value) #~(string-append #$key "=" #$value))
+    ((? string?) #~#$value)
+    (x x)))
+
+(define-maybe string)
+
+(define (serialize-file-like value)
+  #~(format #f "  module ~s~%" #$(normalize-file value)))
+
+(define (string-list? x)
+  (and (list? x)
+       (and-map (match-lambda
+                  (((? string?) (? file-like?)) #t)
+                  ;; TODO: Remove gexps from linux-arguments.
+                  (x (or (string? x) (gexp? x))))
+                x)))
+
+(define (file-like-list? x)
+  (and (list? x) (and-map file-like? x)))
+
+(define (serialize-string-list value)
+  #~(string-join (list #$@(map serialize-string value)) " "))
+
+(define (serialize-file-like-list value)
+  #~(string-concatenate (list #$@(map serialize-file-like value))))
+
+(define (grub-device? x)
+  (or (not x) (string? x) (uuid? x) (file-system-label? x)))
+
+(define (serialize-grub-device device file)
+  "Return the GRUB 'search' command to look for DEVICE, which contains
+FILE, a gexp.  The result is a gexp that can be inserted in the
+grub.cfg-generation code to set the variable VAR.  This procedure is
+able to handle DEVICEs unmounted at evaltime."
+  (define (host-prefix? device)
+    (and (string? device) (string-contains device ":/")))
+  (match device
+    ;; Preferably refer to DEVICE by its UUID or label.  This is more
+    ;; efficient and less ambiguous, see <http://bugs.gnu.org/22281>.
+    ((? uuid?)
+     #~(format #f "search.fs_uuid ~a ~a~%"
+               #$(uuid->string device) #$%boot))
+    ((? file-system-label?)
+     #~(format #f "search.fs_label ~s ~a~%"
+               #$(sanitize (file-system-label->string device)) #$%boot))
+    ((? host-prefix?)
+     ;; If the device is an NFS share, then we assume that the expected
+     ;; file on that device (e.g. the GRUB background image or the kernel)
+     ;; has to be loaded over the network.  Otherwise we would need an
+     ;; additional device information for some local disk to look for that
+     ;; file, which we do not have.
+     ;;
+     ;; TFTP is preferred to HTTP because it is used more widely and
+     ;; specified in standards more widely--especially BOOTP/DHCPv4
+     ;; defines a TFTP server for DHCP option 66, but not HTTP.
+     ;;
+     ;; Note: DHCPv6 specifies option 59 to contain a boot-file-url,
+     ;; which can contain an HTTP or TFTP URL.
+     ;;
+     ;; Note: It is assumed that the file paths are of a similar
+     ;; setup on both the TFTP server and the NFS server (it is
+     ;; not possible to search for files on TFTP).
+     ;;
+     ;; TODO: Allow HTTP.
+     #~(format #f "set ~a=tftp~%" #$%boot))
+    ((or #f (? string?))
+     #~(format #f "search.file ~s ~a~%" #$(sanitize file) #$%boot))))
+
+(define-configuration linux-directive
+  ;; XXX: Does normalize-file work on strings?
+  (extra-initrd maybe-string "Path to out-of-store initrd with secrets.")
+  (initrd file-like "The initial RAM disk to use.")
+  (kernel file-like "The Linux kernel image to boot.")
+  (arguments
+   string-list
+   "The list of extra Linux kernel command-line arguments."))
+
+(define (serialize-linux-directive value normalize-file)
+  (match-record value <linux-directive>
+    (arguments extra-initrd initrd kernel)
+    ;; TODO: Convert menu-entry-initrd to file-like.
+    (let ((initrd #~(readlink #$initrd))
+          (kernel #~(readlink #$kernel)))
+      #~(format #f "  linux ~s ~a~%  initrd ~s~%"
+                #$(normalize-file kernel)
+                ;; GRUB passes the rest of the line _verbatim_.
+                #$(serialize-string-list arguments)
+                (if #$(maybe-value-set? extra-initrd)
+                    ;; XXX: Do not normalize extra-initrd?
+                    (string-append #$(normalize-file extra-initrd)
+                                   "\" \"" #$(normalize-file initrd))
+                    #$(normalize-file initrd))))))
+
+(define-configuration multiboot-directive
+  (kernel file-like "The Multiboot kernel image to boot.")
+  (arguments
+   (string-list '())
+   "The list of Multiboot kernel command-line arguments.")
+  (modules
+   (file-like-list '())
+   "The list of commands for loading Multiboot modules."))
+
+(define (serialize-multiboot-directive value normalize-file)
+  (match-record value <multiboot-directive>
+    (arguments kernel modules)
+    ;; Previously, this provided a (wrong) root= argument.
+    ;; Just don't bother anymore; better less info than
+    ;; wrong info.
+    #~(format #f "  multiboot ~s ~a~%~a"
+              #$(normalize-file kernel)
+              #$(serialize-string-list arguments)
+              #$(serialize-file-like-list modules))))
+
+(define (directive-or-file-like? x)
+  (or (linux-directive? x) (multiboot-directive? x) (file-like? x)))
+
+(define (serialize-directive-or-file-like value)
+  ;; TODO: Use mount-point and subvol to normalize file.
+  (match value
+    ((? linux-directive?)
+     (serialize-linux-directive value normalize-file))
+    ((? multiboot-directive?)
+     (serialize-multiboot-directive value normalize-file))
+    ((? file-like?)
+     #~(format #f "  chainloader ~s~%" #$(normalize-file value)))))
+
+(define-configuration grub-menu-entry
+  (label string "Entry label with e.g. rank, kernel, and date.")
+  (device
+   grub-device
+   ;; XXX: Is NFS exclusive to Linux?
+   "Device UUID or label, NFS path, or block device path, with payload.")
+  (device-mount-point maybe-string "Remove prefix from relevant paths.")
+  (device-subvol maybe-string "Access files from this Btrfs subvolume.")
+  (directive
+   directive-or-file-like
+   "Configuration for a Linux or Multiboot directive, or a file for the
+chainloader directive."))
+
+(define (menu-entry->grub-menu-entry entry extra-initrd)
+  "Temporary compatibility function just for trying out a new thing."
+  (match-menu-entry entry
+    (label device device-mount-point device-subvol linux linux-arguments
+     initrd multiboot-kernel multiboot-arguments multiboot-modules
+     chain-loader)
+    (grub-menu-entry
+      (label label)
+      (device device)
+      (device-mount-point (or device-mount-point %unset-value))
+      (device-subvol (or device-subvol %unset-value))
+      ;; Prefer linux to multiboot to chainloader.
+      (directive (cond
+                   (linux
+                     (linux-directive
+                       (arguments linux-arguments)
+                       (extra-initrd (or extra-initrd %unset-value))
+                       ;; Refer to single file by (sym)link, not string.
+                       ;; TODO: Convert menu-entry-initrd to file-like.
+                       (initrd (computed-file "initrd.cpio.gz"
+                                 #~(symlink #$initrd #$output)))
+                       (kernel (computed-file "bzImage"
+                                 #~(symlink #$linux #$output)))))
+                   (multiboot-kernel
+                     (multiboot-directive
+                       (arguments multiboot-arguments)
+                       (kernel multiboot-kernel)
+                       (modules multiboot-modules)))
+                   (chain-loader chain-loader))))))
+
+(define (serialize-grub-menu-entry value)
+  (let* ((directive (grub-menu-entry-directive value))
+         (file (match directive
+                 ((? linux-directive?)
+                  (linux-directive-kernel directive))
+                 ((? multiboot-directive?)
+                  (multiboot-directive-kernel directive))
+                 ((? file-like?) directive)))
+         (device (grub-menu-entry-device value))
+         ;; XXX: Decouple from directive (file).
+         (search (serialize-grub-device device file))
+         (label (grub-menu-entry-label value))
+         (directive (serialize-directive-or-file-like directive)))
+    #~(format #f "menuentry ~s {~%  ~a~a}~%"
+              #$label #$search #$directive)))
+
+;; E.g. build this file, appended with:
+;; (mixed-text-file "grub-menu-entry.texi"
+;;                  (generate-grub-menu-entry-documentation))
+(define (generate-grub-menu-entry-documentation)
+  (generate-documentation
+   `((grub-menu-entry
+      ,grub-menu-entry-fields
+      (directive linux-directive)
+      (directive multiboot-directive))
+     (linux-directive ,linux-directive-fields)
+     (multiboot-directive ,multiboot-directive-fields))
+   'grub-menu-entry))
 
-;; TODO: use define-configuration.
 (define (make-grub.cfg bootloader-config locale install menu-entries
-                       old-entries terms->str outputs inputs theme)
-  (define (colors->str c)
-    (format #f "~a/~a" (assoc-ref c 'fg) (assoc-ref c 'bg)))
-
+                       old-entries gfxterm? outputs inputs theme)
+  (define (really-mixed-text-file . xs)
+    "Ignores #f arguments and flattens list arguments."
+    (apply mixed-text-file (flatten (filter identity xs))))
   (match-bootloader-configuration
     bootloader-config
     ;; XXX: Separate these fields into another record?
     (default-entry timeout serial-unit serial-speed)
-    #~(call-with-output-file #$output
-        (lambda (port)
-          ;; preamble
-          (format port "\
+    (really-mixed-text-file "grub.cfg" "\
 # This file was generated from your Guix configuration. Any changes
-# will be lost upon reconfiguration~%")
-          #$@(when-list
-        ;; menu settings
-               (and default-entry
-                    #~(format port "set default=~a~%" #$default-entry))
-               (and timeout
-                    #~(format port "set timeout=~a~%" #$timeout))
-        ;; gfxterm setup
-               (and (memq 'gfxterm outputs)
-                    #~(format
-                        port "\
+# will be lost upon reconfiguration\n"
+      ;; menu settings
+      (format #f "~@[set default=~a~%~]" default-entry)
+      (format #f "~@[set timeout=~a~%~]" timeout)
+      ;; gfxterm setup
+      (and gfxterm?
+           (format #f "\
 if loadfont unicode; then
   set gfxmode=~a
   insmod all_video
   insmod gfxterm
 fi~%"
-                        #$(string-join (grub-theme-gfxmode theme) ";")))
-        ;; io
-               (and (or serial-unit serial-speed)
-                     #~(format
-                         port "serial --unit=~a --speed=~a~%"
-                         ;; Documented defaults are unit 0 at 9600 baud.
-                         #$(number->string (or serial-unit 0))
-                         #$(number->string (or serial-speed 9600))))
-               (and (pair? outputs)
-                    #~(format port "terminal_output ~a~%"
-                              #$(terms->str outputs)))
-               (and (pair? inputs)
-                    #~(format port "terminal_input ~a~%"
-                              #$(terms->str inputs)))
-        ;; locale
-               (and locale
-                    #~(format port "\
-set \"locale_dir=($root)~a/locales\"
+                   (string-join (grub-theme-gfxmode theme) ";")))
+      ;; io
+      (and (or serial-unit serial-speed)
+           (format #f "serial~@[ --unit=~d~]~@[ --speed=~d~]~%"
+                   serial-unit serial-speed))
+      (format #f "~@[terminal_output ~a~%~]" outputs)
+      (format #f "~@[terminal_input ~a~%~]" inputs)
+      ;; locale
+      (and locale
+           #~(format #f "\
+set locale_dir=\"($root)~a/locales\"
 set lang=~a~%"
-                              #$(sanitize install)
-                              #$(locale-definition-source
-                                  (locale-name->definition locale))))
-        ;; keyboard layout
-               (and (bootloader-configuration-keyboard-layout
-                      bootloader-config)
-                    #~(format port "\
+                     #$(sanitize install)
+                     #$(locale-definition-source
+                         (locale-name->definition locale))))
+      ;; keyboard layout
+      (and (bootloader-configuration-keyboard-layout bootloader-config)
+           #~(format #f "\
 insmod keylayouts
-keymap \"($root)~a/keymap~%\""
-                              #$(sanitize install)))
-        ;; theme
-               (match-record theme <grub-theme>
-                 (image color-normal color-highlight)
-                 (and image
-                      #~(format port "\
-insmod png
-if background_image \"($root)~a/image.png\"; then
-  set color_normal=~a
-  set color_highlight=~a
-else
-  set menu_color_normal=cyan/blue
-  set menu_color_highlight=white/blue
-fi~%"                           #$(sanitize install)
-                                #$(colors->str color-normal)
-                                #$(colors->str color-highlight)))))
-        ;; menu entries
-        #$@menu-entries
-        #$@(if (pair? old-entries)
-               (append (list #~(format
-                                 port "submenu ~s {~%"
-                                 "GNU system, old configurations..."))
-                       old-entries
-                       (list #~(format port "}~%")))
-               '())
-        (format port "\
+keymap \"($root)~a/keymap\"~%"
+                     #$(sanitize install)))
+      (serialize-grub-theme theme install)
+      ;; menu entries
+      menu-entries
+      (and (pair? old-entries)
+           (cons "submenu \"GNU system, old configurations...\" {\n"
+                 ;; Do not indent: initrd line is >80 columns anyway.
+                 (append old-entries (list "}\n"))))
+      "\
 if [ \"${grub_platform}\" == efi ]; then
   menuentry \"Firmware setup\" {
     fwsetup
   }
-fi~%")))))
+fi\n")))
 
 (define* (grub.cfg #:key bootloader-config
                          current-boot-alternative
@@ -437,28 +549,26 @@ (define* (grub.cfg #:key bootloader-config
     (menu-entries targets extra-initrd theme terminal-outputs
      terminal-inputs)
     (define (entries->gexp entries)
-      (map (cut menu-entry->gexp <> extra-initrd #~port)
+      (map (compose serialize-grub-menu-entry
+                    (cut menu-entry->grub-menu-entry <> extra-initrd))
            entries))
-
+    (define (terms->str terms)
+      (and (pair? terms) (format #f "~{~a~^ ~}" terms)))
     (let* ((current-entry (boot-alternative->menu-entry
                             current-boot-alternative))
            (entries (entries->gexp (cons current-entry menu-entries)))
            (old-entries (entries->gexp (map boot-alternative->menu-entry
                                             old-boot-alternatives)))
-           (terms->str (compose string-join (cut map symbol->string <>)))
+           (gfxterm? (or (not terminal-outputs)
+                         (memq 'gfxterm terminal-outputs)))
            ;; Use the values provided, or the defaults otherwise.
-           (outputs (or terminal-outputs '(gfxterm)))
-           (inputs (or terminal-inputs '()))
+           (outputs (or (and=> terminal-outputs terms->str) "gfxterm"))
+           (inputs (and=> terminal-inputs terms->str))
            (theme (or theme (grub-theme))))
-      (and=>
-        (with-targets targets
-          (('install => (install :devpath))
-           (make-grub.cfg bootloader-config locale install entries
-                          old-entries terms->str outputs inputs theme)))
-        (cut computed-file "grub.cfg" <>
-             ;; Since this file is rather unique, there's no point in
-             ;; trying to substitute it.
-             #:options '(#:local-build? #t #:substitutable? #f))))))
+      (with-targets targets
+        (('install => (install :devpath))
+         (make-grub.cfg bootloader-config locale install entries
+                        old-entries gfxterm? outputs inputs theme))))))
 
 (define (keyboard-layout-file layout grub)
   "Process the X keyboard layout description LAYOUT, a <keyboard-layout>