linux-initrd: Factorize cpio archive creation.

* gnu/build/linux-initrd.scm: New file.
* gnu-system.am (GNU_SYSTEM_MODULES): Add it.
* gnu/system/linux-initrd.scm (expression->initrd): Use (gnu build
  linux-initrd) and 'write-cpio-archive' instead of the inlined code.

gnu-system.am

@@ -283,6 +283,7 @@ GNU_SYSTEM_MODULES =				\
   gnu/build/file-systems.scm			\
   gnu/build/install.scm				\
   gnu/build/linux-boot.scm			\
+  gnu/build/linux-initrd.scm			\
   gnu/build/vm.scm
 
 

gnu/build/linux-initrd.scm

@@ -0,0 +1,70 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2013, 2014 Ludovic Courtès <ludo@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 build linux-initrd)
+  #:use-module (ice-9 popen)
+  #:use-module (ice-9 ftw)
+  #:export (write-cpio-archive))
+
+;;; Commentary:
+;;;
+;;; Tools to create Linux initial RAM disks ("initrds").  Initrds are
+;;; essentially gzipped cpio archives, with a '/init' executable that the
+;;; kernel runs at boot time.
+;;;
+;;; Code:
+
+(define* (write-cpio-archive output directory
+                             #:key
+                             (compress? #t)
+                             (cpio "cpio") (gzip "gzip"))
+  "Write a cpio archive containing DIRECTORY to file OUTPUT, using CPIO.  When
+COMPRESS? is true, compress it using GZIP.  On success, return OUTPUT."
+  (let ((pipe (open-pipe* OPEN_WRITE cpio "-o" "-O" output
+                          "-H" "newc" "--null"
+                          "--no-absolute-filenames")))
+    (define (print0 file)
+      (format pipe "~a\0" file))
+
+    ;; Note: as per `ramfs-rootfs-initramfs.txt', always add directory entries
+    ;; before the files that are inside of it: "The Linux kernel cpio
+    ;; extractor won't create files in a directory that doesn't exist, so the
+    ;; directory entries must go before the files that go in those
+    ;; directories."
+
+    ;; XXX: Use a deterministic order.
+    (file-system-fold (const #t)
+                      (lambda (file stat result)   ; leaf
+                        (print0 file))
+                      (lambda (dir stat result)    ; down
+                        (unless (string=? dir directory)
+                          (print0 dir)))
+                      (const #f)                   ; up
+                      (const #f)                   ; skip
+                      (const #f)
+                      #f
+                      directory)
+
+    (and (zero? (close-pipe pipe))
+         (or (not compress?)
+             (and (zero? (system* gzip "--best" output))
+                  (rename-file (string-append output ".gz")
+                               output))
+             output))))
+
+;;; linux-initrd.scm ends here

gnu/system/linux-initrd.scm

@@ -75,9 +75,10 @@ initrd."
   (mlet* %store-monad ((source   (imported-modules modules))
                        (compiled (compiled-modules modules)))
     (define builder
-      ;; TODO: Move most of this code to (gnu build linux-boot).
+      ;; TODO: Move most of this code to (gnu build linux-initrd).
       #~(begin
-          (use-modules (guix build utils)
+          (use-modules (gnu build linux-initrd)
+                       (guix build utils)
                        (ice-9 pretty-print)
                        (ice-9 popen)
                        (ice-9 match)
@@ -87,9 +88,7 @@ initrd."
                        (rnrs bytevectors)
                        ((system foreign) #:select (sizeof)))
 
-          (let ((cpio    (string-append #$cpio "/bin/cpio"))
+          (let ((modules #$source)
-                (gzip    (string-append #$gzip "/bin/gzip"))
-                (modules #$source)
                 (gos     #$compiled)
                 (scm-dir (string-append "share/guile/" (effective-version)))
                 (go-dir  (format #f ".cache/guile/ccache/~a-~a-~a-~a"
@@ -162,39 +161,13 @@ initrd."
               (for-each (cut utime <> 0 0 0 0)
                         (find-files "." ".*"))
 
-              (system* cpio "--version")
+              (write-cpio-archive (string-append #$output "/initrd") "."
-              (let ((pipe (open-pipe* OPEN_WRITE cpio "-o"
+                                  #:cpio (string-append #$cpio "/bin/cpio")
-                                      "-O" (string-append #$output "/initrd")
+                                  #:gzip (string-append #$gzip "/bin/gzip"))))))
-                                      "-H" "newc" "--null")))
-                (define print0
-                  (let ((len (string-length "./")))
-                    (lambda (file)
-                      (format pipe "~a\0" (string-drop file len)))))
-
-                ;; Note: as per `ramfs-rootfs-initramfs.txt', always add
-                ;; directory entries before the files that are inside of it: "The
-                ;; Linux kernel cpio extractor won't create files in a directory
-                ;; that doesn't exist, so the directory entries must go before
-                ;; the files that go in those directories."
-                (file-system-fold (const #t)
-                                  (lambda (file stat result) ; leaf
-                                    (print0 file))
-                                  (lambda (dir stat result) ; down
-                                    (unless (string=? dir ".")
-                                      (print0 dir)))
-                                  (const #f)         ; up
-                                  (const #f)         ; skip
-                                  (const #f)
-                                  #f
-                                  ".")
-
-                (and (zero? (close-pipe pipe))
-                     (with-directory-excursion #$output
-                       (and (zero? (system* gzip "--best" "initrd"))
-                            (rename-file "initrd.gz" "initrd")))))))))
 
    (gexp->derivation name builder
-                     #:modules '((guix build utils)))))
+                     #:modules '((guix build utils)
+                                 (gnu build linux-initrd)))))
 
 (define (file-system->spec fs)
   "Return a list corresponding to file-system FS that can be passed to the