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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."
+
+ ;; Note: don't use '--no-absolute-filenames' since that strips leading
+ ;; slashes from symlink targets.
+ (let ((pipe (open-pipe* OPEN_WRITE cpio "-o" "-O" output
+ "-H" "newc" "--null")))
+ (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