vm: Use 'invoke' instead of 'system*'.

* gnu/build/vm.scm (load-in-linux-vm, initialize-partition-table)
(create-ext-file-system, create-fat-file-system)
(install-efi, make-iso9660-image): Use 'invoke' instead
of (unless (zero? (system* ...)) (error ...)).

gnu/build/vm.scm

@@ -1,5 +1,5 @@
 ;;; GNU Guix --- Functional package management for GNU
-;;; Copyright © 2013, 2014, 2015, 2016, 2017 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2013, 2014, 2015, 2016, 2017, 2018 Ludovic Courtès <ludo@gnu.org>
 ;;; Copyright © 2016 Christopher Allan Webber <cwebber@dustycloud.org>
 ;;; Copyright © 2016, 2017 Leo Famulari <leo@famulari.name>
 ;;; Copyright © 2017 Mathieu Othacehe <m.othacehe@gmail.com>
@@ -121,10 +121,8 @@ the #:references-graphs parameter of 'derivation'."
     (format #t "creating ~a image of ~,2f MiB...~%"
             disk-image-format (/ disk-image-size (expt 2 20)))
     (force-output)
-    (unless (zero? (system* "qemu-img" "create" "-f" disk-image-format
+    (invoke "qemu-img" "create" "-f" disk-image-format output
-                            output
              (number->string disk-image-size)))
-      (error "qemu-img failed")))
 
   (mkdir "xchg")
 
@@ -136,8 +134,7 @@ the #:references-graphs parameter of 'derivation'."
           graph-files))
     (_ #f))
 
-  (unless (zero?
+  (apply invoke qemu "-nographic" "-no-reboot"
-           (apply system* qemu "-nographic" "-no-reboot"
          "-m" (number->string memory-size)
          "-object" "rng-random,filename=/dev/urandom,id=guixsd-vm-rng"
          "-device" "virtio-rng-pci,rng=guixsd-vm-rng"
@@ -159,8 +156,7 @@ the #:references-graphs parameter of 'derivation'."
                                          ",format=" disk-image-format
                                          ",id=myhd"))
               '())
-                   arch-specific-flags)))
+          arch-specific-flags))
-    (error "qemu failed" qemu))
 
   ;; When MAKE-DISK-IMAGE? is true, the image is in OUTPUT already.
   (unless make-disk-image?
@@ -240,10 +236,9 @@ actual /dev name based on DEVICE."
                                      partition-size)
                             partitions)
                        ", "))
-  (unless (zero? (apply system* "parted" "--script"
+  (apply invoke "parted" "--script"
          device "mklabel" label-type
-                        (options partitions offset)))
+         (options partitions offset))
-    (error "failed to create partition table"))
 
   ;; Set the 'device' field of each partition.
   (reverse
@@ -265,7 +260,7 @@ actual /dev name based on DEVICE."
   "Create an ext-family file system of TYPE on PARTITION.  If LABEL is true,
 use that as the volume name.  If UUID is true, use it as the partition UUID."
   (format #t "creating ~a partition...\n" type)
-  (unless (zero? (apply system* (string-append "mkfs." type)
+  (apply invoke (string-append "mkfs." type)
          "-F" partition
          `(,@(if label
                  `("-L" ,label)
@@ -273,7 +268,6 @@ use that as the volume name.  If UUID is true, use it as the partition UUID."
            ,@(if uuid
                  `("-U" ,(uuid->string uuid))
                  '()))))
-    (error "failed to create partition")))
 
 (define* (create-fat-file-system partition
                                  #:key label uuid)
@@ -282,11 +276,8 @@ will be determined based on file system size.  If LABEL is true, use that as the
 volume name."
   ;; FIXME: UUID is ignored!
   (format #t "creating FAT partition...\n")
-  (unless (zero? (apply system* "mkfs.fat" partition
+  (apply invoke "mkfs.fat" partition
-                        (if label
+         (if label `("-n" ,label) '())))
-                            `("-n" ,label)
-                            '())))
-    (error "failed to create FAT partition")))
 
 (define* (format-partition partition type
                            #:key label uuid)
@@ -388,12 +379,11 @@ SYSTEM-DIRECTORY is the name of the directory of the 'system' derivation."
     (setenv "TMPDIR" esp)
 
     (mkdir-p efi-directory)
-    (unless (zero? (system* grub-mkstandalone "-O" (car efi-targets)
+    (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=" config-file)))
+            (string-append "boot/grub/grub.cfg=" config-file))))
-      (error "failed to create GRUB EFI image"))))
 
 (define* (make-iso9660-image grub config-file os-drv target
                              #:key (volume-id "GuixSD_image") (volume-uuid #f)
@@ -416,7 +406,7 @@ GRUB configuration and OS-DRV as the stuff in it."
                    #:deduplicate? #f))
                 closures))
 
-    (unless (zero? (apply system*
+    (apply invoke
            `(,grub-mkrescue "-o" ,target
                             ,(string-append "boot/grub/grub.cfg=" config-file)
                             ,(string-append "gnu/store=" os-drv "/..")
@@ -435,8 +425,7 @@ GRUB configuration and OS-DRV as the stuff in it."
                                                       (not (char=? #\- value)))
                                                     (iso9660-uuid->string
                                                      volume-uuid)))
-                                  `()))))
+                                  `())))))
-      (error "failed to create ISO9660 image"))))
 
 (define* (initialize-hard-disk device
                                #:key