190 lines
6.9 KiB
Nix
190 lines
6.9 KiB
Nix
# This module creates a bootable SD card image containing the given NixOS
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# configuration. The generated image is MBR partitioned, with a FAT
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# /boot/firmware partition, and ext4 root partition. The generated image
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# is sized to fit its contents, and a boot script automatically resizes
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# the root partition to fit the device on the first boot.
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#
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# The firmware partition is built with expectation to hold the Raspberry
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# Pi firmware and bootloader, and be removed and replaced with a firmware
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# build for the target SoC for other board families.
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#
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# The derivation for the SD image will be placed in
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# config.system.build.sdImage
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{ config, lib, pkgs, ... }:
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with lib;
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let
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rootfsImage = pkgs.callPackage ../../../lib/make-ext4-fs.nix ({
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inherit (config.sdImage) storePaths;
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populateImageCommands = config.sdImage.populateRootCommands;
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volumeLabel = "NIXOS_SD";
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} // optionalAttrs (config.sdImage.rootPartitionUUID != null) {
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uuid = config.sdImage.rootPartitionUUID;
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});
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in
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{
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options.sdImage = {
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imageName = mkOption {
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default = "${config.sdImage.imageBaseName}-${config.system.nixos.label}-${pkgs.stdenv.hostPlatform.system}.img";
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description = ''
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Name of the generated image file.
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'';
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};
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imageBaseName = mkOption {
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default = "nixos-sd-image";
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description = ''
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Prefix of the name of the generated image file.
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'';
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};
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storePaths = mkOption {
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type = with types; listOf package;
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example = literalExample "[ pkgs.stdenv ]";
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description = ''
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Derivations to be included in the Nix store in the generated SD image.
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'';
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};
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firmwarePartitionID = mkOption {
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type = types.string;
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default = "0x2178694e";
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description = ''
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Volume ID for the /boot/firmware partition on the SD card. This value
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must be a 32-bit hexadecimal number.
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'';
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};
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rootPartitionUUID = mkOption {
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type = types.nullOr types.string;
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default = null;
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example = "14e19a7b-0ae0-484d-9d54-43bd6fdc20c7";
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description = ''
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UUID for the main NixOS partition on the SD card.
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'';
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};
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firmwareSize = mkOption {
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type = types.int;
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# As of 2019-05-31 the Raspberry pi firmware + u-bot takes ~13MiB
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default = 20;
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description = ''
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Size of the /boot/firmware partition, in megabytes.
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'';
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};
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populateFirmwareCommands = mkOption {
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example = literalExample "'' cp \${pkgs.myBootLoader}/u-boot.bin firmware/ ''";
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description = ''
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Shell commands to populate the ./firmware directory.
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All files in that directory are copied to the
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/boot/firmware partition on the SD image.
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'';
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};
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populateRootCommands = mkOption {
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example = literalExample "''\${extlinux-conf-builder} -t 3 -c \${config.system.build.toplevel} -d ./files/boot''";
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description = ''
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Shell commands to populate the ./files directory.
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All files in that directory are copied to the
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root (/) partition on the SD image. Use this to
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populate the ./files/boot (/boot) directory.
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'';
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};
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};
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config = {
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fileSystems = {
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"/boot/firmware" = {
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device = "/dev/disk/by-label/FIRMWARE";
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fsType = "vfat";
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# Alternatively, this could be removed from the configuration.
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# The filesystem is not needed at runtime, it could be treated
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# as an opaque blob instead of a discrete FAT32 filesystem.
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options = [ "nofail" "noauto" ];
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};
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"/" = {
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device = "/dev/disk/by-label/NIXOS_SD";
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fsType = "ext4";
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};
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};
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sdImage.storePaths = [ config.system.build.toplevel ];
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system.build.sdImage = pkgs.callPackage ({ stdenv, dosfstools, e2fsprogs, mtools, libfaketime, utillinux }: stdenv.mkDerivation {
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name = config.sdImage.imageName;
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nativeBuildInputs = [ dosfstools e2fsprogs mtools libfaketime utillinux ];
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buildCommand = ''
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mkdir -p $out/nix-support $out/sd-image
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export img=$out/sd-image/${config.sdImage.imageName}
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echo "${pkgs.stdenv.buildPlatform.system}" > $out/nix-support/system
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echo "file sd-image $img" >> $out/nix-support/hydra-build-products
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# Create the image file sized to fit /boot/firmware and /, plus 20M of slack
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rootSizeBlocks=$(du -B 512 --apparent-size ${rootfsImage} | awk '{ print $1 }')
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firmwareSizeBlocks=$((${toString config.sdImage.firmwareSize} * 1024 * 1024 / 512))
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imageSize=$((rootSizeBlocks * 512 + firmwareSizeBlocks * 512 + 20 * 1024 * 1024))
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truncate -s $imageSize $img
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# type=b is 'W95 FAT32', type=83 is 'Linux'.
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# The "bootable" partition is where u-boot will look file for the bootloader
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# information (dtbs, extlinux.conf file).
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sfdisk $img <<EOF
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label: dos
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label-id: ${config.sdImage.firmwarePartitionID}
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start=8M, size=$firmwareSizeBlocks, type=b
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start=${toString (8 + config.sdImage.firmwareSize)}M, type=83, bootable
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EOF
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# Copy the rootfs into the SD image
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eval $(partx $img -o START,SECTORS --nr 2 --pairs)
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dd conv=notrunc if=${rootfsImage} of=$img seek=$START count=$SECTORS
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# Create a FAT32 /boot/firmware partition of suitable size into firmware_part.img
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eval $(partx $img -o START,SECTORS --nr 1 --pairs)
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truncate -s $((SECTORS * 512)) firmware_part.img
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faketime "1970-01-01 00:00:00" mkfs.vfat -i ${config.sdImage.firmwarePartitionID} -n FIRMWARE firmware_part.img
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# Populate the files intended for /boot/firmware
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mkdir firmware
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${config.sdImage.populateFirmwareCommands}
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# Copy the populated /boot/firmware into the SD image
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(cd firmware; mcopy -psvm -i ../firmware_part.img ./* ::)
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# Verify the FAT partition before copying it.
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fsck.vfat -vn firmware_part.img
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dd conv=notrunc if=firmware_part.img of=$img seek=$START count=$SECTORS
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'';
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}) {};
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boot.postBootCommands = ''
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# On the first boot do some maintenance tasks
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if [ -f /nix-path-registration ]; then
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# Figure out device names for the boot device and root filesystem.
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rootPart=$(readlink -f /dev/disk/by-label/NIXOS_SD)
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bootDevice=$(lsblk -npo PKNAME $rootPart)
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# Resize the root partition and the filesystem to fit the disk
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echo ",+," | sfdisk -N2 --no-reread $bootDevice
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${pkgs.parted}/bin/partprobe
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${pkgs.e2fsprogs}/bin/resize2fs $rootPart
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# Register the contents of the initial Nix store
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${config.nix.package.out}/bin/nix-store --load-db < /nix-path-registration
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# nixos-rebuild also requires a "system" profile and an /etc/NIXOS tag.
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touch /etc/NIXOS
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${config.nix.package.out}/bin/nix-env -p /nix/var/nix/profiles/system --set /run/current-system
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# Prevents this from running on later boots.
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rm -f /nix-path-registration
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fi
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'';
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};
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}
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