127 lines
4.2 KiB
Nix
127 lines
4.2 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 /boot
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# partition, and ext4 root partition. The generated image is sized to fit
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# its contents, and a boot script automatically resizes the root partition
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# to fit the device on the first boot.
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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 = import ../../../lib/make-ext4-fs.nix {
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inherit pkgs;
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inherit (config.sdImage) storePaths;
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volumeLabel = "NIXOS_SD";
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};
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in
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{
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options.sdImage = {
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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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bootSize = mkOption {
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type = types.int;
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default = 120;
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description = ''
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Size of the /boot partition, in megabytes.
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'';
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};
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populateBootCommands = mkOption {
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example = literalExample "'' cp \${pkgs.myBootLoader}/u-boot.bin boot/ ''";
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description = ''
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Shell commands to populate the ./boot directory.
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All files in that directory are copied to the
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/boot partition on the SD image.
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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" = {
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device = "/dev/disk/by-label/NIXOS_BOOT";
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fsType = "vfat";
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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.stdenv.mkDerivation {
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name = "sd-image-${pkgs.stdenv.system}.img";
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buildInputs = with pkgs; [ dosfstools e2fsprogs mtools libfaketime utillinux ];
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buildCommand = ''
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# Create the image file sized to fit /boot and /, plus 20M of slack
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rootSizeBlocks=$(du -B 512 --apparent-size ${rootfsImage} | awk '{ print $1 }')
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bootSizeBlocks=$((${toString config.sdImage.bootSize} * 1024 * 1024 / 512))
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imageSize=$((rootSizeBlocks * 512 + bootSizeBlocks * 512 + 20 * 1024 * 1024))
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truncate -s $imageSize $out
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# type=b is 'W95 FAT32', type=83 is 'Linux'.
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sfdisk $out <<EOF
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label: dos
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label-id: 0x2178694e
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start=8M, size=$bootSizeBlocks, type=b, bootable
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start=${toString (8 + config.sdImage.bootSize)}M, type=83
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EOF
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# Copy the rootfs into the SD image
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eval $(partx $out -o START,SECTORS --nr 2 --pairs)
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dd conv=notrunc if=${rootfsImage} of=$out seek=$START count=$SECTORS
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# Create a FAT32 /boot partition of suitable size into bootpart.img
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eval $(partx $out -o START,SECTORS --nr 1 --pairs)
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truncate -s $((SECTORS * 512)) bootpart.img
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faketime "1970-01-01 00:00:00" mkfs.vfat -i 0x2178694e -n NIXOS_BOOT bootpart.img
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# Populate the files intended for /boot
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mkdir boot
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${config.sdImage.populateBootCommands}
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# Copy the populated /boot into the SD image
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(cd boot; mcopy -bpsvm -i ../bootpart.img ./* ::)
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dd conv=notrunc if=bootpart.img of=$out seek=$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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