[PATCH] scripts/make-gpt.sh: make GPT offset configurable

[Ivan Nikolaenko <ivan.nikolaenko@unikie.com>]

These changes can be used in an external configuration layer as
follows:
    overlays = [
      (self: super:
        {
            gptOffset = 9437184;
        })
    ];

Signed-off-by: Ivan Nikolaenko <ivan.nikolaenko@unikie.com>
---

This patch is not a solution but just a proposal about how things can be done.
There is at least one another way of doing this (having our own make-gpt.sh script),
but I thought that editing of the current one is better way.

Also I don't know should we also consider other images and rootfs be fixed this way.

 img/live/Makefile    |  3 ++-
 img/live/default.nix |  1 +
 scripts/make-gpt.sh  | 22 ++++++++++++++++++++--
 3 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/img/live/Makefile b/img/live/Makefile
index 9815c88..5a29156 100644
--- a/img/live/Makefile
+++ b/img/live/Makefile
@@ -19,7 +19,8 @@ build/live.img: $(SCRIPTS)/format-uuid.sh $(SCRIPTS)/make-gpt.sh build/boot.fat
 	    build/boot.fat:c12a7328-f81f-11d2-ba4b-00a0c93ec93b \
 	    build/rootfs.verity.superblock:2c7357ed-ebd2-46d9-aec1-23d437ec2bf5:$$($(SCRIPTS)/format-uuid.sh "$$(dd if=build/rootfs.verity.roothash bs=32 skip=1 count=1 status=none)") \
 	    $(ROOT_FS):4f68bce3-e8cd-4db1-96e7-fbcaf984b709:$$($(SCRIPTS)/format-uuid.sh "$$(head -c 32 build/rootfs.verity.roothash)") \
-	    $(EXT_FS):9293e1ff-cee4-4658-88be-898ec863944f
+	    $(EXT_FS):9293e1ff-cee4-4658-88be-898ec863944f \
+	    --gptoffset=$(GPT_OFFSET)
 	mv $@.tmp $@
 
 build/spectrum.conf: build/rootfs.verity.roothash
diff --git a/img/live/default.nix b/img/live/default.nix
index 5461384..c529206 100644
--- a/img/live/default.nix
+++ b/img/live/default.nix
@@ -34,6 +34,7 @@ stdenvNoCC.mkDerivation {
   KERNEL = "${rootfs.kernel}/${stdenv.hostPlatform.linux-kernel.target}";
   ROOT_FS = rootfs;
   SYSTEMD_BOOT_EFI = "${systemd}/lib/systemd/boot/efi/systemd-bootx64.efi";
+  GPT_OFFSET=pkgs.gptOffset or null;
 
   buildFlags = [ "build/live.img" ];
   makeFlags = [ "SCRIPTS=${scripts}" ];
diff --git a/scripts/make-gpt.sh b/scripts/make-gpt.sh
index 56076d3..e8dd067 100755
--- a/scripts/make-gpt.sh
+++ b/scripts/make-gpt.sh
@@ -41,8 +41,25 @@ shift
 nl=$'\n'
 table="label: gpt"
 
-# Keep 1MiB free at the start, and 1MiB free at the end.
-gptBytes=$TWO_MiB
+TEMP=`getopt -o g:: --long gptoffset:: -- "$@"`
+eval set -- "$TEMP"
+
+while true ; do
+    case "$1" in
+        -g|--gptoffset)
+            gptBytes=$2 ; shift 2 ;;
+        --) shift ; break ;;
+        *) break ;;
+    esac
+done
+
+if [ -z "$gptBytes" ]
+then
+      gptBytes=${TWO_MiB}
+fi
+
+FIRST_LBA="$(expr ${gptBytes} / 1024)"
+
 for partition; do
 	sizeMiB="$(sizeMiB "$(partitionPath "$partition")")"
 	table="$table${nl}size=${sizeMiB}MiB,$(awk -f "$scriptsDir/sfdisk-field.awk" -v partition="$partition")"
@@ -52,6 +69,7 @@ done
 rm -f "$out"
 truncate -s "$gptBytes" "$out"
 sfdisk "$out" <<EOF
+first-lba: ${FIRST_LBA}
 $table
 EOF
 
-- 
2.25.1