+ (call-with-port
+ ;; Do not use "call-with-output-file" that would truncate the file.
+ (open-file-output-port device
+ (file-options no-truncate no-fail)
+ (buffer-mode block)
+ ;; Use the binary-friendly ISO-8859-1
+ ;; encoding.
+ (make-transcoder (latin-1-codec)))
+ (lambda (output)
+ (seek output offset SEEK_SET)
+ (put-bytevector output bv)))))))
+
+\f
+;;;
+;;; EFI bootloader.
+;;;
+
+(define (install-efi grub grub-config esp)
+ "Write a self-contained GRUB EFI loader to the mounted ESP using GRUB-CONFIG."
+ (let* ((system %host-type)
+ ;; Hard code the output location to a well-known path recognized by
+ ;; compliant firmware. See "3.5.1.1 Removable Media Boot Behaviour":
+ ;; http://www.uefi.org/sites/default/files/resources/UEFI%20Spec%202_6.pdf
+ (grub-mkstandalone (string-append grub "/bin/grub-mkstandalone"))
+ (efi-directory (string-append esp "/EFI/BOOT"))
+ ;; Map grub target names to boot file names.
+ (efi-targets (cond ((string-prefix? "x86_64" system)
+ '("x86_64-efi" . "BOOTX64.EFI"))
+ ((string-prefix? "i686" system)
+ '("i386-efi" . "BOOTIA32.EFI"))
+ ((string-prefix? "armhf" system)
+ '("arm-efi" . "BOOTARM.EFI"))
+ ((string-prefix? "aarch64" system)
+ '("arm64-efi" . "BOOTAA64.EFI")))))
+ ;; grub-mkstandalone requires a TMPDIR to prepare the firmware image.
+ (setenv "TMPDIR" esp)
+
+ (mkdir-p efi-directory)
+ (invoke grub-mkstandalone "-O" (car efi-targets)
+ "-o" (string-append efi-directory "/"
+ (cdr efi-targets))
+ ;; Graft the configuration file onto the image.
+ (string-append "boot/grub/grub.cfg=" grub-config))))
+
+(define (install-efi-loader grub-efi esp)
+ "Install in ESP directory the given GRUB-EFI bootloader. Configure it to
+load the Grub bootloader located in the 'Guix_image' root partition."
+ (let ((grub-config "grub.cfg"))
+ (call-with-output-file grub-config
+ (lambda (port)
+ ;; Create a tiny configuration file telling the embedded grub where to
+ ;; load the real thing. XXX This is quite fragile, and can prevent
+ ;; the image from booting when there's more than one volume with this
+ ;; label present. Reproducible almost-UUIDs could reduce the risk
+ ;; (not eliminate it).
+ (format port
+ "insmod part_msdos~@
+ search --set=root --label Guix_image~@
+ configfile /boot/grub/grub.cfg~%")))
+ (install-efi grub-efi grub-config esp)
+ (delete-file grub-config)))