[PATCH] installer: operate on FAT image directly

[Alyssa Ross <hi@alyssa.is>]

---
It feels cleaner to me to operate directly on the FAT image, rather
than constructing the directory on the build filesystem and then
copying it into the FAT image at the end.  But, I'm wondering if maybe
there's a reason it's better to do it the other way that I've missed?

 installer/default.nix | 25 +++++++++++++------------
 1 file changed, 13 insertions(+), 12 deletions(-)

diff --git a/installer/default.nix b/installer/default.nix
index f7e84ac..0818091 100644
--- a/installer/default.nix
+++ b/installer/default.nix
@@ -24,6 +24,7 @@ let
 
   esp = runCommand "esp.img" {
     nativeBuildInputs = [ grub libfaketime dosfstools mtools ];
+    grubTargetDir = "${grub}/lib/grub/${grub.grubTarget}";
     # Definition copied from util/grub-install-common.c.
     # Last checked: GRUB 2.06
     pkglib_DATA = [
@@ -31,23 +32,23 @@ let
       "parttool.lst" "video.lst" "crypto.lst" "terminal.lst" "modinfo.sh"
     ];
   } ''
-    mkdir -p files/grub/${grub.grubTarget}
-    cp ${grubCfg} files/grub/grub.cfg
-    cp ${grub}/lib/grub/${grub.grubTarget}/*.mod files/grub/${grub.grubTarget}
+    truncate -s 15M $out
+    faketime "1970-01-01 00:00:00" mkfs.vfat -i 0x2178694e -n EFI $out
+    mmd -i $out ::/EFI ::/EFI/BOOT \
+        ::/grub ::/grub/${grub.grubTarget} ::/grub/fonts
+
+    mcopy -i $out ${grubCfg} ::/grub/grub.cfg
+    mcopy -i $out $grubTargetDir/*.mod ::/grub/${grub.grubTarget}
     for file in $pkglib_DATA; do
-        path="${grub}/lib/grub/${grub.grubTarget}/$file"
-        ! [ -e "$path" ] || cp "$path" files/grub/${grub.grubTarget}
+        path="$grubTargetDir/$file"
+        ! [ -e "$path" ] || mcopy -i $out "$path" ::/grub/${grub.grubTarget}
     done
+    mcopy -i $out ${grub}/share/grub/unicode.pf2 ::/grub/fonts
 
-    install -D ${grub}/share/grub/unicode.pf2 files/grub/fonts/unicode.pf2
     grub-mkimage -o grubx64.efi -p "(hd0,gpt1)/grub" -O ${grub.grubTarget} part_gpt fat
-    install -D grubx64.efi files/EFI/BOOT/BOOTX64.EFI
+    mcopy -i $out grubx64.efi ::/EFI/BOOT/BOOTX64.EFI
 
-    img=$out
-    truncate -s 15M $img
-    faketime "1970-01-01 00:00:00" mkfs.vfat -i 0x2178694e -n EFI $img
-    (cd files; mcopy -psvm -i $img ./* ::)
-    fsck.vfat -vn $img
+    fsck.vfat -n $out
   '';
 
   installer = runCommand "installer.img" {
-- 
2.33.0