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|
# This module creates a bootable SD card image containing the given NixOS
# configuration. The generated image is MBR partitioned, with a FAT /boot
# 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 derivation for the SD image will be placed in
# config.system.build.sdImage
{ config, lib, pkgs, ... }:
with lib;
let
rootfsImage = import ../../../lib/make-ext4-fs.nix {
inherit pkgs;
inherit (config.sdImage) storePaths;
volumeLabel = "NIXOS_SD";
};
in
{
options.sdImage = {
storePaths = mkOption {
type = with types; listOf package;
example = literalExample "[ pkgs.stdenv ]";
description = ''
Derivations to be included in the Nix store in the generated SD image.
'';
};
bootSize = mkOption {
type = types.int;
default = 120;
description = ''
Size of the /boot partition, in megabytes.
'';
};
populateBootCommands = mkOption {
example = literalExample "'' cp \${pkgs.myBootLoader}/u-boot.bin boot/ ''";
description = ''
Shell commands to populate the ./boot directory.
All files in that directory are copied to the
/boot partition on the SD image.
'';
};
};
config = {
fileSystems = {
"/boot" = {
device = "/dev/disk/by-label/NIXOS_BOOT";
fsType = "vfat";
};
"/" = {
device = "/dev/disk/by-label/NIXOS_SD";
fsType = "ext4";
};
};
sdImage.storePaths = [ config.system.build.toplevel ];
system.build.sdImage = pkgs.stdenv.mkDerivation {
name = "sd-image-${pkgs.stdenv.system}.img";
buildInputs = with pkgs; [ dosfstools e2fsprogs mtools libfaketime utillinux ];
buildCommand = ''
# Create the image file sized to fit /boot and /, plus 20M of slack
rootSizeBlocks=$(du -B 512 --apparent-size ${rootfsImage} | awk '{ print $1 }')
bootSizeBlocks=$((${toString config.sdImage.bootSize} * 1024 * 1024 / 512))
imageSize=$((rootSizeBlocks * 512 + bootSizeBlocks * 512 + 20 * 1024 * 1024))
truncate -s $imageSize $out
# type=b is 'W95 FAT32', type=83 is 'Linux'.
sfdisk $out <<EOF
label: dos
label-id: 0x2178694e
start=8M, size=$bootSizeBlocks, type=b, bootable
start=${toString (8 + config.sdImage.bootSize)}M, type=83
EOF
# Copy the rootfs into the SD image
eval $(partx $out -o START,SECTORS --nr 2 --pairs)
dd conv=notrunc if=${rootfsImage} of=$out seek=$START count=$SECTORS
# Create a FAT32 /boot partition of suitable size into bootpart.img
eval $(partx $out -o START,SECTORS --nr 1 --pairs)
truncate -s $((SECTORS * 512)) bootpart.img
faketime "1970-01-01 00:00:00" mkfs.vfat -i 0x2178694e -n NIXOS_BOOT bootpart.img
# Populate the files intended for /boot
mkdir boot
${config.sdImage.populateBootCommands}
# Copy the populated /boot into the SD image
(cd boot; mcopy -bpsvm -i ../bootpart.img ./* ::)
dd conv=notrunc if=bootpart.img of=$out seek=$START count=$SECTORS
'';
};
boot.postBootCommands = ''
# On the first boot do some maintenance tasks
if [ -f /nix-path-registration ]; then
# Figure out device names for the boot device and root filesystem.
rootPart=$(readlink -f /dev/disk/by-label/NIXOS_SD)
bootDevice=$(lsblk -npo PKNAME $rootPart)
# Resize the root partition and the filesystem to fit the disk
echo ",+," | sfdisk -N2 --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
'';
};
}
|