From 0d0d649e70af99d23f4f42ef19253923ced1c971 Mon Sep 17 00:00:00 2001
From: Emery Hemingway <ehmry@posteo.net>
Date: Thu, 10 Dec 2020 20:21:02 +0100
Subject: [PATCH] fixup! fixup! fixup! Boot from USB

---
 nixos-modules/lib/make-bootable-image.nix | 69 ++++++++++++++++++++++
 nixos-modules/lib/make-esp-fs.nix         | 72 +++++++++++++++++++++++
 nixos-modules/partition-type              |  1 +
 nixos-modules/store-fs-uuid               |  1 +
 4 files changed, 143 insertions(+)
 create mode 100644 nixos-modules/lib/make-bootable-image.nix
 create mode 100644 nixos-modules/lib/make-esp-fs.nix
 create mode 100644 nixos-modules/partition-type
 create mode 100644 nixos-modules/store-fs-uuid

diff --git a/nixos-modules/lib/make-bootable-image.nix b/nixos-modules/lib/make-bootable-image.nix
new file mode 100644
index 0000000..3a12cbf
--- /dev/null
+++ b/nixos-modules/lib/make-bootable-image.nix
@@ -0,0 +1,69 @@
+# Builds a compressed EFI System Partition image
+{ config, pkgs, espImage, storeFsImage }:
+
+pkgs.stdenv.mkDerivation {
+  name = "boot.qcow2";
+
+  nativeBuildInputs = with pkgs.buildPackages; [
+    config.system.build.qemu
+    utillinux
+    zstd
+  ];
+
+  buildCommand = ''
+    img=./temp.raw
+    blockSize=512
+    sectorSize=$(( $blockSize * 1 ))
+    imgBytes=0
+
+    espSectorOffset=2048
+    esbByteOffset=$(( $espSectorOffset * $sectorSize ))
+
+    # Pad the front of the image
+    echo "Pad front of image with " $esbByteOffset " bytes"
+    truncate --size=$esbByteOffset $img
+
+    # Concatentenate the ESP
+    echo "Concatenate ESP ${espImage}"
+    zstdcat ${espImage} >> $img
+
+    imgBytes=$(stat --format=%s $img)
+    echo "Image is $(( $imgBytes >> 20 )) MiB with ESP partition"
+
+    nixSectorOffset=$(( ($imgBytes + $sectorSize - 1) / $sectorSize ))
+    nixByteOffset=$(( $nixSectorOffset * $sectorSize ))
+
+    # Pad the ESP
+    echo "Pad end of ESP with " $(( $nixByteOffset - $imgBytes )) " bytes"
+    truncate --size=$nixByteOffset $img
+
+    # Concatenate the nix partition
+    echo "Concatenate store ${storeFsImage}"
+    zstdcat ${storeFsImage} >> $img
+
+    imgBytes=$(stat --format=%s $img)
+    echo "Image is $(( $imgBytes >> 20 )) MiB with store partition"
+
+    endSectorOffset=$(( ($(stat --format=%s $img) + $sectorSize + 1) / $sectorSize ))
+    endByteOffset=$(( $endSectorOffset * $sectorSize ))
+
+    # Pad the end of the image
+    echo "Pad end of store with $(( $endByteOffset - $imgBytes )) bytes"
+    truncate --size=$endByteOffset $img
+
+    imgBytes=$(stat --format=%s $img)
+    echo "Image is $(( $imgBytes >> 20 )) MiB with final padding"
+
+    efiUuid=C12A7328-F81F-11D2-BA4B-00A0C93EC93B
+
+    # Create the partition table
+    sfdisk $img <<EOF
+      label: gpt
+      label-id: 44444444-4444-4444-8888-888888888888
+      start=$nixSectorOffset, type=${config.genode.boot.storePartUuid}
+      start=$espSectorOffset, type=$efiUuid
+    EOF
+
+    qemu-img convert $img $out
+  '';
+}
diff --git a/nixos-modules/lib/make-esp-fs.nix b/nixos-modules/lib/make-esp-fs.nix
new file mode 100644
index 0000000..4e8233c
--- /dev/null
+++ b/nixos-modules/lib/make-esp-fs.nix
@@ -0,0 +1,72 @@
+# Builds a compressed EFI System Partition image
+{ config, pkgs }:
+
+let
+  grub' = pkgs.buildPackages.grub2_efi;
+
+  # Name used by UEFI for architectures.
+  targetArch = if pkgs.stdenv.isi686 || config.boot.loader.grub.forcei686 then
+    "ia32"
+  else if pkgs.stdenv.isx86_64 then
+    "x64"
+  else if pkgs.stdenv.isAarch64 then
+    "aa64"
+  else
+    throw "Unsupported architecture";
+
+in pkgs.stdenv.mkDerivation {
+  name = "esp.img.zst";
+
+  nativeBuildInputs = with pkgs.buildPackages; [ grub' dosfstools mtools zstd ];
+
+  MODULES = [
+    "configfile"
+    "efi_gop"
+    "efi_uga"
+    "ext2"
+    "gzio"
+    "multiboot"
+    "multiboot2"
+    "normal"
+    "part_gpt"
+    "search_fs_uuid"
+  ];
+
+  buildCommand = ''
+    img=tmp.raw
+    bootdir=EFI/boot/
+    mkdir -p $bootdir
+
+    cat <<EOF > embedded.cfg
+    insmod configfile
+    insmod efi_gop
+    insmod efi_uga
+    insmod ext2
+    insmod normal
+    insmod part_gpt
+    insmod search_fs_uuid
+    search.fs_uuid ${config.genode.boot.storeFsUuid} root
+    set prefix=($root)/boot/grub
+    configfile /boot/grub/grub.cfg
+    EOF
+
+    grub-script-check embedded.cfg
+
+    ${grub'}/bin/grub-mkimage \
+      --config=embedded.cfg \
+      --output=$bootdir/boot${targetArch}.efi \
+      --prefix=/boot/grub \
+      --format=${grub'.grubTarget} \
+      $MODULES
+
+    # Make the ESP image twice as large as necessary
+    imageBytes=$(du --summarize --block-size=4096 --total $bootdir | tail -1 | awk '{ print int($1 * 8192) }')
+
+    truncate --size=$imageBytes $img
+    mkfs.vfat -n EFIBOOT --invariant $img
+    mcopy -sv -i $img EFI ::
+    fsck.vfat -nv $img
+
+    zstd --verbose --no-progress ./$img -o $out
+  '';
+}
diff --git a/nixos-modules/partition-type b/nixos-modules/partition-type
new file mode 100644
index 0000000..2cca25d
--- /dev/null
+++ b/nixos-modules/partition-type
@@ -0,0 +1 @@
+"24b69406-18a1-428d-908e-d21a1437122c"
diff --git a/nixos-modules/store-fs-uuid b/nixos-modules/store-fs-uuid
new file mode 100644
index 0000000..7325548
--- /dev/null
+++ b/nixos-modules/store-fs-uuid
@@ -0,0 +1 @@
+"9668f8dd-d9a0-4398-a55a-0d499d5e5cbb"