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diff --git a/gnu/build/linux-initrd.scm b/gnu/build/linux-initrd.scm
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+;;; 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