image: Use file system options in make-vfat-image.

* gnu/build/image.scm (make-vfat-image): Use file system options.

Change-Id: I791aadd2803d1ef96fc79cf8910a74a0083d2b6e
Signed-off-by: Ludovic Courtès <ludo@gnu.org>

doc/guix.texi

@@ -48348,7 +48348,8 @@ and @code{"ext4"}.
 @item @code{file-system-options} (default: @code{'()})
 The partition file system creation options that should be passed to the
 partition creation tool, as a list of strings.  This is only supported
-when creating @code{"ext4"} partitions.
+when creating @code{"vfat"}, @code{"fat16"}, @code{"fat32"} or
+@code{"ext4"} partitions.
 
 See the @code{"extended-options"} man page section of the
 @code{"mke2fs"} tool for a more complete reference.

gnu/build/image.scm

@@ -105,17 +105,21 @@ turn doesn't take any constant overhead into account, force a 1-MiB minimum."
   "Handle the creation of VFAT partition images.  See 'make-partition-image'."
   (let ((size (partition-size partition))
         (label (partition-label partition))
-        (flags (partition-flags partition)))
+        (flags (partition-flags partition))
+        (fs-options (partition-file-system-options partition)))
     (apply invoke "fakeroot" "mkdosfs" "-n" label "-C" target
-                          "-F" (number->string fs-bits)
-                          (size-in-kib
-                           (if (eq? size 'guess)
-                               (estimate-partition-size root)
-                               size))
-                    ;; u-boot in particular needs the formatted block
-                    ;; size and the physical block size to be equal.
-                    ;; TODO: What about 4k blocks?
-                    (if (member 'esp flags) (list "-S" "512") '()))
+           "-F" (number->string fs-bits)
+           (size-in-kib
+            (if (eq? size 'guess)
+                (estimate-partition-size root)
+                size))
+           ;; u-boot in particular needs the formatted block
+           ;; size and the physical block size to be equal.
+           ;; TODO: What about 4k blocks?
+           (if (and (member 'esp flags)
+                    (not (member "-S" fs-options)))
+               (append (list "-S" "512") fs-options)
+               fs-options))
     (for-each (lambda (file)
                 (unless (member file '("." ".."))
                   (invoke "mcopy" "-bsp" "-i" target