bootloader: Factorize write-file-on-device.

* gnu/bootloader/extlinux.scm (install-extlinux): Factorize bootloader
writing in a new procedure write-file-on-device defined in (gnu build
bootloader).
* gnu/build/bootloader.scm: New file.
* gnu/local.mk (GNU_SYSTEM_MODULES): Add new file.
* gnu/system/vm.scm (qemu-img): Adapt to import and use (gnu build bootloader)
module during derivation building.
* gnu/scripts/system.scm (bootloader-installer-derivation): Ditto.

1 files changed, 3 insertions, 7 deletions

diff --git a/gnu/bootloader/extlinux.scm b/gnu/bootloader/extlinux.scm
index 9b6e2c7f2a2..f7820a37a48 100644
--- a/gnu/bootloader/extlinux.scm
+++ b/gnu/bootloader/extlinux.scm
@@ -20,6 +20,7 @@
 (define-module (gnu bootloader extlinux)
   #:use-module (gnu bootloader)
   #:use-module (gnu system)
+  #:use-module (gnu build bootloader)
   #:use-module (gnu packages bootloaders)
   #:use-module (guix gexp)
   #:use-module (guix monads)
@@ -95,13 +96,8 @@ TIMEOUT ~a~%"
                   (find-files syslinux-dir "\\.c32$"))
         (unless
             (and (zero? (system* extlinux "--install" install-dir))
-                 (call-with-input-file (string-append syslinux-dir "/" #$mbr)
-                   (lambda (input)
-                     (let ((bv (get-bytevector-n input 440)))
-                       (call-with-output-file device
-                         (lambda (output)
-                           (put-bytevector output bv))
-                         #:binary #t)))))
+                 (write-file-on-device
+                  (string-append syslinux-dir "/" #$mbr) 440 device 0))
           (error "failed to install SYSLINUX")))))
 
 (define install-extlinux-mbr