system: Add 'initrd-modules' field.

* gnu/system.scm (<operating-system>)[initrd-modules]: New field.
(operating-system-initrd-file): Pass #:linux-modules to 'make-initrd'.
* gnu/system/linux-initrd.scm (default-initrd-modules): New procedure.
(%base-initrd-modules): New macro.
(base-initrd): Add #:linux-modules and honor it.
* gnu/system/install.scm (embedded-installation-os): Use
'initrd-modules' instead of 'initrd'.
* gnu/tests/install.scm (%raid-root-os): Likewise.
* doc/guix.texi (operating-system Reference): Add 'initrd-modules'.
(Initial RAM Disk): Document it.  Adjust example to not use
 #:extra-modules.

doc/guix.texi

@@ -8889,11 +8889,16 @@ the command-line of the kernel---e.g., @code{("console=ttyS0")}.
 @item @code{bootloader}
 The system bootloader configuration object.  @xref{Bootloader Configuration}.
-@item @code{initrd} (default: @code{base-initrd})
+@item @code{initrd-modules} (default: @code{%base-initrd-modules})
 @cindex initrd
 @cindex initial RAM disk
-A two-argument monadic procedure that returns an initial RAM disk for
-the Linux kernel.  @xref{Initial RAM Disk}.
+The list of Linux kernel modules that need to be available in the
+initial RAM disk.  @xref{Initial RAM Disk}.
+
+@item @code{initrd} (default: @code{base-initrd})
+A monadic procedure that returns an initial RAM disk for the Linux
+kernel.  This field is provided to support low-level customization and
+should rarely be needed for casual use.  @xref{Initial RAM Disk}.
 @item @code{firmware} (default: @var{%base-firmware})
 @cindex firmware
@@ -19768,7 +19773,27 @@ root file system as well as an initialization script.  The latter is
 responsible for mounting the real root file system, and for loading any
 kernel modules that may be needed to achieve that.
-The @code{initrd} field of an @code{operating-system} declaration allows
+The @code{initrd-modules} field of an @code{operating-system}
+declaration allows you to specify Linux-libre kernel modules that must
+be available in the initrd.  In particular, this is where you would list
+modules needed to actually drive the hard disk where your root partition
+is---although the default value of @code{initrd-modules} should cover
+most use cases.  For example, assuming you need the @code{megaraid_sas}
+module in addition to the default modules to be able to access your root
+file system, you would write:
+
+@example
+(operating-system
+  ;; @dots{}
+  (initrd-modules (cons "megaraid_sas" %base-initrd-modules)))
+@end example
+
+@defvr {Scheme Variable} %base-initrd-modules
+This is the list of kernel modules included in the initrd by default.
+@end defvr
+
+Furthermore, if you need lower-level customization, the @code{initrd}
+field of an @code{operating-system} declaration allows
 you to specify which initrd you would like to use.  The @code{(gnu
 system linux-initrd)} module provides three ways to build an initrd: the
 high-level @code{base-initrd} procedure and the low-level
@@ -19781,11 +19806,10 @@ system declaration like this:
 @example
 (initrd (lambda (file-systems . rest)
-          ;; Create a standard initrd that has modules "foo.ko"
-          ;; and "bar.ko", as well as their dependencies, in
-          ;; addition to the modules available by default.
+          ;; Create a standard initrd but set up networking
+          ;; with the parameters QEMU expects by default.
           (apply base-initrd file-systems
-                 #:extra-modules '("foo" "bar")
+                 #:qemu-networking? #t
                  rest)))
 @end example

gnu/system.scm

@@ -74,6 +74,7 @@ (define-module (gnu system)
             operating-system-kernel
             operating-system-kernel-file
             operating-system-kernel-arguments
+            operating-system-initrd-modules
             operating-system-initrd
             operating-system-users
             operating-system-groups
@@ -154,6 +155,10 @@ (define-record-type* <operating-system> operating-system
 
   (initrd operating-system-initrd                 ; (list fs) -> M derivation
           (default base-initrd))
+  (initrd-modules operating-system-initrd-modules ; list of strings
+                  (thunked)                       ; it's system-dependent
+                  (default %base-initrd-modules))
+
   (firmware operating-system-firmware             ; list of packages
             (default %base-firmware))
 
@@ -846,6 +851,8 @@ (define make-initrd
 
   (mlet %store-monad ((initrd (make-initrd boot-file-systems
                                            #:linux (operating-system-kernel os)
+                                           #:linux-modules
+                                           (operating-system-initrd-modules os)
                                            #:mapped-devices mapped-devices)))
     (return (file-append initrd "/initrd"))))
 

gnu/system/install.scm

 ;;; GNU Guix --- Functional package management for GNU
-;;; Copyright © 2014, 2015, 2016, 2017 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2014, 2015, 2016, 2017, 2018 Ludovic Courtès <ludo@gnu.org>
 ;;; Copyright © 2015 Mark H Weaver <mhw@netris.org>
 ;;; Copyright © 2016 Andreas Enge <andreas@enge.fr>
 ;;; Copyright © 2017 Marius Bakke <mbakke@fastmail.com>
@@ -396,10 +396,7 @@ (define* (embedded-installation-os bootloader bootloader-target tty
     (kernel-arguments
      (cons (string-append "console=" tty)
            (operating-system-user-kernel-arguments installation-os)))
-    (initrd (lambda (fs . rest)
-              (apply base-initrd fs
-                     #:extra-modules extra-modules
-                     rest)))))
+    (initrd-modules (append extra-modules %base-initrd-modules))))
 
 (define beaglebone-black-installation-os
   (embedded-installation-os u-boot-beaglebone-black-bootloader

gnu/system/linux-initrd.scm

@@ -43,6 +43,7 @@ (define-module (gnu system linux-initrd)
   #:use-module (srfi srfi-1)
   #:use-module (srfi srfi-26)
   #:export (expression->initrd
+            %base-initrd-modules
             raw-initrd
             file-system-packages
             base-initrd))
@@ -277,14 +278,31 @@ (define (file-system-modules file-systems)
   (append-map (compose file-system-type-modules file-system-type)
               file-systems))
 
+(define* (default-initrd-modules #:optional (system (%current-system)))
+  "Return the list of modules included in the initrd by default."
+  `("ahci"                                  ;for SATA controllers
+    "usb-storage" "uas"                     ;for the installation image etc.
+    "usbhid" "hid-generic" "hid-apple"      ;keyboards during early boot
+    "dm-crypt" "xts" "serpent_generic" "wp512" ;for encrypted root partitions
+    "nls_iso8859-1"                            ;for `mkfs.fat`, et.al
+    ,@(if (string-match "^(x86_64|i[3-6]86)-" system)
+          '("pata_acpi" "pata_atiixp"    ;for ATA controllers
+            "isci")                      ;for SAS controllers like Intel C602
+          '())))
+
+(define-syntax %base-initrd-modules
+  ;; This more closely matches our naming convention.
+  (identifier-syntax (default-initrd-modules)))
+
 (define* (base-initrd file-systems
                       #:key
                       (linux linux-libre)
+                      (linux-modules '())
                       (mapped-devices '())
                       qemu-networking?
                       volatile-root?
                       (virtio? #t)
-                      (extra-modules '())
+                      (extra-modules '())         ;deprecated
                       (on-error 'debug))
   "Return a monadic derivation that builds a generic initrd, with kernel
 modules taken from LINUX.  FILE-SYSTEMS is a list of file-systems to be
@@ -307,17 +325,9 @@ (define virtio-modules
     '("virtio_pci" "virtio_balloon" "virtio_blk" "virtio_net"
       "virtio_console"))
 
-  (define linux-modules
+  (define linux-modules*
     ;; Modules added to the initrd and loaded from the initrd.
-    `("ahci"                                  ;for SATA controllers
-      "usb-storage" "uas"                     ;for the installation image etc.
-      "usbhid" "hid-generic" "hid-apple"      ;keyboards during early boot
-      "dm-crypt" "xts" "serpent_generic" "wp512" ;for encrypted root partitions
-      "nls_iso8859-1"                            ;for `mkfs.fat`, et.al
-      ,@(if (string-match "^(x86_64|i[3-6]86)-" (%current-system))
-            '("pata_acpi" "pata_atiixp"    ;for ATA controllers
-              "isci")                      ;for SAS controllers like Intel C602
-            '())
+    `(,@linux-modules
       ,@(if (or virtio? qemu-networking?)
             virtio-modules
             '())
@@ -332,7 +342,7 @@ (define helper-packages
 
   (raw-initrd file-systems
               #:linux linux
-              #:linux-modules linux-modules
+              #:linux-modules linux-modules*
               #:mapped-devices mapped-devices
               #:helper-packages helper-packages
               #:qemu-networking? qemu-networking?

gnu/tests/install.scm

 ;;; GNU Guix --- Functional package management for GNU
-;;; Copyright © 2016, 2017 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2016, 2017, 2018 Ludovic Courtès <ludo@gnu.org>
 ;;; Copyright © 2017 Tobias Geerinckx-Rice <me@tobias.gr>
 ;;;
 ;;; This file is part of GNU Guix.
@@ -565,11 +565,10 @@ (define-os-with-source (%raid-root-os %raid-root-os-source)
                  (bootloader grub-bootloader)
                  (target "/dev/vdb")))
     (kernel-arguments '("console=ttyS0"))
-    (initrd (lambda (file-systems . rest)
-              ;; Add a kernel module for RAID-0 (aka. "stripe").
-              (apply base-initrd file-systems
-                     #:extra-modules '("raid0")
-                     rest)))
+
+    ;; Add a kernel module for RAID-0 (aka. "stripe").
+    (initrd-modules (cons "raid0" %base-initrd-modules))
+
     (mapped-devices (list (mapped-device
                            (source (list "/dev/vda2" "/dev/vda3"))
                            (target "/dev/md0")