kiosk/sd-image/sd-image.nix

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2024-12-07 16:44:37 -05:00
# This module was lifted from nixpkgs installer code. It is modified
# so as to not import all-hardware. The goal here is to write the
# nixos image for a raspberry pi to an sd-card in a way so that we can
# pop it in and go. We don't need to support many possible hardware
# targets since we know we are targeting raspberry pi products.
# This module creates a bootable SD card image containing the given NixOS
# configuration. The generated image is MBR partitioned, with a FAT
# /boot/firmware partition, and ext4 root partition. The generated image
# is sized to fit its contents, and a boot script automatically resizes
# the root partition to fit the device on the first boot.
#
# The firmware partition is built with expectation to hold the Raspberry
# Pi firmware and bootloader, and be removed and replaced with a firmware
# build for the target SoC for other board families.
#
# The derivation for the SD image will be placed in
# config.system.build.sdImage
{ modulesPath, config, lib, pkgs, ... }:
with lib;
let
rootfsImage = pkgs.callPackage "${modulesPath}/../lib/make-ext4-fs.nix" ({
inherit (config.sdImage) storePaths;
compressImage = false;
populateImageCommands = config.sdImage.populateRootCommands;
volumeLabel = "NIXOS_SD";
} // optionalAttrs (config.sdImage.rootPartitionUUID != null) {
uuid = config.sdImage.rootPartitionUUID;
});
in
{
imports = [ ];
options.sdImage = {
imageName = mkOption {
default =
"${config.sdImage.imageBaseName}-${config.system.nixos.label}-${pkgs.stdenv.hostPlatform.system}.img";
description = ''
Name of the generated image file.
'';
};
imageBaseName = mkOption {
default = "nixos-sd-image";
description = ''
Prefix of the name of the generated image file.
'';
};
storePaths = mkOption {
type = with types; listOf package;
example = literalExpression "[ pkgs.stdenv ]";
description = ''
Derivations to be included in the Nix store in the generated SD image.
'';
};
firmwarePartitionOffset = mkOption {
type = types.int;
default = 8;
description = ''
Gap in front of the /boot/firmware partition, in mebibytes (1024×1024
bytes).
Can be increased to make more space for boards requiring to dd u-boot
SPL before actual partitions.
Unless you are building your own images pre-configured with an
installed U-Boot, you can instead opt to delete the existing `FIRMWARE`
partition, which is used **only** for the Raspberry Pi family of
hardware.
'';
};
firmwarePartitionID = mkOption {
type = types.str;
default = "0x2178694e";
description = ''
Volume ID for the /boot/firmware partition on the SD card. This value
must be a 32-bit hexadecimal number.
'';
};
rootPartitionUUID = mkOption {
type = types.nullOr types.str;
default = null;
example = "14e19a7b-0ae0-484d-9d54-43bd6fdc20c7";
description = ''
UUID for the filesystem on the main NixOS partition on the SD card.
'';
};
firmwareSize = mkOption {
type = types.int;
# As of 2019-08-18 the Raspberry pi firmware + u-boot takes ~18MiB
default = 128;
description = ''
Size of the /boot/firmware partition, in megabytes.
'';
};
populateFirmwareCommands = mkOption {
example =
literalExpression "'' cp \${pkgs.myBootLoader}/u-boot.bin firmware/ ''";
description = ''
Shell commands to populate the ./firmware directory.
All files in that directory are copied to the
/boot/firmware partition on the SD image.
'';
};
populateRootCommands = mkOption {
example = literalExpression
"''\${config.boot.loader.generic-extlinux-compatible.populateCmd} -c \${config.system.build.toplevel} -d ./files/boot''";
description = ''
Shell commands to populate the ./files directory.
All files in that directory are copied to the
root (/) partition on the SD image. Use this to
populate the ./files/boot (/boot) directory.
'';
};
postBuildCommands = mkOption {
example = literalExpression
"'' dd if=\${pkgs.myBootLoader}/SPL of=$img bs=1024 seek=1 conv=notrunc ''";
default = "";
description = ''
Shell commands to run after the image is built.
Can be used for boards requiring to dd u-boot SPL before actual partitions.
'';
};
compressImage = mkOption {
type = types.bool;
default = false;
description = ''
Whether the SD image should be compressed using
<command>zstd</command>.
'';
};
expandOnBoot = mkOption {
type = types.bool;
default = true;
description = ''
Whether to configure the sd image to expand it's partition on boot.
'';
};
};
config = {
fileSystems = {
"/boot/firmware" = {
device = "/dev/disk/by-label/${config.raspberry-pi-nix.firmware-partition-label}";
fsType = "vfat";
};
"/" = {
device = "/dev/disk/by-label/NIXOS_SD";
fsType = "ext4";
};
};
sdImage.storePaths = [ config.system.build.toplevel ];
system.build.sdImage = pkgs.callPackage
({ stdenv, dosfstools, e2fsprogs, mtools, libfaketime, util-linux, zstd }:
stdenv.mkDerivation {
name = config.sdImage.imageName;
nativeBuildInputs =
[ dosfstools e2fsprogs mtools libfaketime util-linux zstd ];
inherit (config.sdImage) compressImage;
buildCommand = ''
mkdir -p $out/nix-support $out/sd-image
export img=$out/sd-image/${config.sdImage.imageName}
echo "${pkgs.stdenv.buildPlatform.system}" > $out/nix-support/system
if test -n "$compressImage"; then
echo "file sd-image $img.zst" >> $out/nix-support/hydra-build-products
else
echo "file sd-image $img" >> $out/nix-support/hydra-build-products
fi
echo "Decompressing rootfs image"
cp "${rootfsImage}" ./root-fs.img
# Gap in front of the first partition, in MiB
gap=${toString config.sdImage.firmwarePartitionOffset}
# Create the image file sized to fit /boot/firmware and /, plus slack for the gap.
rootSizeBlocks=$(du -B 512 --apparent-size ./root-fs.img | awk '{ print $1 }')
firmwareSizeBlocks=$((${
toString config.sdImage.firmwareSize
} * 1024 * 1024 / 512))
imageSize=$((rootSizeBlocks * 512 + firmwareSizeBlocks * 512 + gap * 1024 * 1024))
truncate -s $imageSize $img
# type=b is 'W95 FAT32', type=83 is 'Linux'.
# The "bootable" partition is where u-boot will look file for the bootloader
# information (dtbs, extlinux.conf file).
sfdisk $img <<EOF
label: dos
label-id: ${config.sdImage.firmwarePartitionID}
start=''${gap}M, size=$firmwareSizeBlocks, type=b
start=$((gap + ${
toString config.sdImage.firmwareSize
}))M, type=83, bootable
EOF
# Copy the rootfs into the SD image
eval $(partx $img -o START,SECTORS --nr 2 --pairs)
dd conv=notrunc if=./root-fs.img of=$img seek=$START count=$SECTORS
# Create a FAT32 /boot/firmware partition of suitable size into firmware_part.img
eval $(partx $img -o START,SECTORS --nr 1 --pairs)
truncate -s $((SECTORS * 512)) firmware_part.img
faketime "1970-01-01 00:00:00" mkfs.vfat -i ${config.sdImage.firmwarePartitionID} -n ${config.raspberry-pi-nix.firmware-partition-label} firmware_part.img
# Populate the files intended for /boot/firmware
mkdir firmware
${config.sdImage.populateFirmwareCommands}
# Copy the populated /boot/firmware into the SD image
(cd firmware; mcopy -psvm -i ../firmware_part.img ./* ::)
# Verify the FAT partition before copying it.
fsck.vfat -vn firmware_part.img
dd conv=notrunc if=firmware_part.img of=$img seek=$START count=$SECTORS
${config.sdImage.postBuildCommands}
if test -n "$compressImage"; then
zstd -T$NIX_BUILD_CORES --rm $img
fi
'';
})
{ };
boot.postBootCommands = lib.mkIf config.sdImage.expandOnBoot ''
# On the first boot do some maintenance tasks
if [ -f /nix-path-registration ]; then
set -euo pipefail
set -x
# Figure out device names for the boot device and root filesystem.
rootPart=$(${pkgs.util-linux}/bin/findmnt -n -o SOURCE /)
bootDevice=$(lsblk -npo PKNAME $rootPart)
partNum=$(lsblk -npo MAJ:MIN $rootPart | ${pkgs.gawk}/bin/awk -F: '{print $2}')
# Resize the root partition and the filesystem to fit the disk
echo ",+," | sfdisk -N$partNum --no-reread $bootDevice
${pkgs.parted}/bin/partprobe
${pkgs.e2fsprogs}/bin/resize2fs $rootPart
# Register the contents of the initial Nix store
${config.nix.package.out}/bin/nix-store --load-db < /nix-path-registration
# nixos-rebuild also requires a "system" profile and an /etc/NIXOS tag.
touch /etc/NIXOS
${config.nix.package.out}/bin/nix-env -p /nix/var/nix/profiles/system --set /run/current-system
# Prevents this from running on later boots.
rm -f /nix-path-registration
fi
'';
};
}