280 lines
9.2 KiB
Nix
280 lines
9.2 KiB
Nix
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{ pkgs
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, lib
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, name ? "nixos-disk-image"
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, # The NixOS configuration to be installed onto the disk image.
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config
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, # The size of the disk, in megabytes. If "auto", the size is calculated based
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# on the contents copied to it and `extraSize` is taken into account.
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diskSize ? "auto"
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, # Extra disk space, in megabytes. Added to the image if diskSize "auto" is
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# used.
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extraSize ? 512
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, # Swap space, in megabytes. Addeded to the image unless set to null.
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swapSize ? 512
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, # The unique identifier for the swap partition.
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swapUUID ? "44444444-4444-4444-8888-888888888887"
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, # The label given to the swap partition.
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swapLabel ? "swap"
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, # Whether to invoke `switch-to-configuration boot` during image creation.
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installBootLoader ? true
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, # The filesystem label.
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label ? "nixos"
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, # The initial NixOS configuration file set at `/etc/nixos/configuration.nix`.
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configFile ? null
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, # Disk image format, one of qcow2, qcow2-compressed, vdi, vpc, raw.
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format ? "raw"
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, # The root Filesystem Unique Identifier.
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rootFSUID ? "F222513B-DED1-49FA-B591-20CE86A2FE7F"
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, # Whether a nix channel based on the current source tree should be
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# made available inside the image. Useful for interactive use of nix
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# utils, but changes the hash of the image when the sources are
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# updated.
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copyChannel ? true
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, # Shell code executed after the VM has finished.
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postVM ? ""
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, # Guest memory size
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memSize ? 1024
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}:
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let
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format' = if format == "qcow2-compressed" then "qcow2" else format;
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compress = lib.optionalString (format == "qcow2-compressed") "-c";
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filename = "nixos." + {
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qcow2 = "qcow2";
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vdi = "vdi";
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vpc = "vhd";
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raw = "img";
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}.${format'} or format';
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swapPartition = "1";
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rootPartition = "2";
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swapEnd = toString (1 + swapSize);
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nixpkgs = lib.cleanSource pkgs.path;
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# FIXME: merge with channel.nix / make-channel.nix.
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channelSources = pkgs.runCommand "nixos-${config.system.nixos.version}" {} ''
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mkdir -p $out
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cp -prd ${nixpkgs.outPath} $out/nixos
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chmod -R u+w $out/nixos
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if [ ! -e $out/nixos/nixpkgs ]; then
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ln -s . $out/nixos/nixpkgs
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fi
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rm -rf $out/nixos/.git
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echo -n ${config.system.nixos.versionSuffix} > $out/nixos/.version-suffix
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'';
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binPath = lib.makeBinPath (with pkgs; [
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rsync
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util-linux
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parted
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e2fsprogs
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lkl
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config.system.build.nixos-install
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config.system.build.nixos-enter
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nix
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systemdMinimal
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gptfdisk
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] ++ stdenv.initialPath);
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closureInfo = pkgs.closureInfo {
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rootPaths = [ config.system.build.toplevel ] ++
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lib.optional copyChannel channelSources;
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};
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# ext4fs block size (not block device sector size)
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blockSize = toString (4 * 1024);
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prepareImage = ''
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export PATH=${binPath}
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# Yes, mkfs.ext4 takes different units in different contexts. Fun.
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sectorsToKilobytes() {
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echo $(( ( "$1" * 512 ) / 1024 ))
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}
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sectorsToBytes() {
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echo $(( "$1" * 512 ))
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}
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# Given lines of numbers, adds them together
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sum_lines() {
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local acc=0
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while read -r number; do
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acc=$((acc+number))
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done
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echo "$acc"
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}
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mebibyte=$(( 1024 * 1024 ))
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# Approximative percentage of reserved space in an ext4 fs over 512MiB.
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# 0.05208587646484375 × 1000, integer part: 52
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compute_fudge() {
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echo $(( $1 * 52 / 1000 ))
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}
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mkdir $out
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root="$PWD/root"
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mkdir -p $root
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export HOME=$TMPDIR
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# Provide a Nix database so that nixos-install can copy closures.
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export NIX_STATE_DIR=$TMPDIR/state
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nix-store --load-db < ${closureInfo}/registration
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chmod 755 "$TMPDIR"
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echo "running nixos-install..."
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nixos-install --root $root --no-bootloader --no-root-passwd \
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--system ${config.system.build.toplevel} \
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${if copyChannel then "--channel ${channelSources}" else "--no-channel-copy"} \
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--substituters ""
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diskImage=nixos.raw
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${if diskSize == "auto" then ''
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# Add the 1MiB aligned reserved space (includes MBR)
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reservedSpace=$(( mebibyte ))
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swapSpace=$((
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$(numfmt --from=iec '${toString swapSize}M') + reservedSpace
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))
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extraSpace=$((
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$(numfmt --from=iec '${toString extraSize}M') + reservedSpace
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))
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# Compute required space in filesystem blocks
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diskUsage=$(
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find . ! -type d -print0 |
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du --files0-from=- --apparent-size --block-size "${blockSize}" |
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cut -f1 |
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sum_lines
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)
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# Each inode takes space!
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numInodes=$(find . | wc -l)
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# Convert to bytes, inodes take two blocks each!
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diskUsage=$(( (diskUsage + 2 * numInodes) * ${blockSize} ))
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# Then increase the required space to account for the reserved blocks.
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fudge=$(compute_fudge $diskUsage)
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requiredFilesystemSpace=$(( diskUsage + fudge ))
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diskSize=$(( requiredFilesystemSpace + swapSpace + extraSpace ))
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# Round up to the nearest mebibyte. This ensures whole 512 bytes sector
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# sizes in the disk image and helps towards aligning partitions optimally.
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if (( diskSize % mebibyte )); then
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diskSize=$(( ( diskSize / mebibyte + 1) * mebibyte ))
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fi
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truncate -s "$diskSize" $diskImage
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printf "Automatic disk size...\n"
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printf " Closure space use: %d bytes\n" $diskUsage
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printf " fudge: %d bytes\n" $fudge
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printf " Filesystem size needed: %d bytes\n" $requiredFilesystemSpace
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printf " Swap space: %d bytes\n" $swapSpace
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printf " Extra space: %d bytes\n" $extraSpace
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printf " Disk image size: %d bytes\n" $diskSize
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'' else ''
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truncate -s ${toString diskSize}M $diskImage
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''}
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parted --script $diskImage -- mklabel msdos
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parted --script $diskImage -- \
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mkpart primary linux-swap 1MiB ${swapEnd}MiB \
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mkpart primary ext4 ${swapEnd}MiB -1
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# Get start & length of the root partition in sectors to $START and
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# $SECTORS.
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eval $(partx $diskImage -o START,SECTORS --nr ${rootPartition} --pairs)
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mkfs.ext4 -b ${blockSize} -F -L ${label} $diskImage -E \
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offset=$(sectorsToBytes $START) $(sectorsToKilobytes $SECTORS)K
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echo "copying staging root to image..."
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cptofs -p -P ${rootPartition} -t ext4 -i $diskImage $root/* / ||
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(echo >&2 "ERROR: cptofs failed. diskSize might be too small for closure."; exit 1)
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'';
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moveOrConvertImage = ''
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${if format' == "raw" then "mv $diskImage $out/${filename}" else ''
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${pkgs.qemu-utils}/bin/qemu-img convert -f raw -O ${format'} ${compress} \
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$diskImage $out/${filename}
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''}
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diskImage=$out/${filename}
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'';
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buildImage = pkgs.vmTools.runInLinuxVM (
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pkgs.runCommand name {
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preVM = prepareImage;
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buildInputs = with pkgs; [ util-linux e2fsprogs dosfstools ];
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postVM = moveOrConvertImage + postVM;
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inherit memSize;
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} ''
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export PATH=${binPath}:$PATH
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rootDisk="/dev/vda${rootPartition}"
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# It is necessary to set root filesystem unique identifier in advance,
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# otherwise the bootloader might get the wrong one and fail to boot. At
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# the end, we reset again because we want deterministic timestamps.
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tune2fs -T now -U ${rootFSUID} -c 0 -i 0 $rootDisk
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# Make systemd-boot find ESP without udev.
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mkdir /dev/block
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ln -s /dev/vda1 /dev/block/254:1
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mountPoint=/mnt
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mkdir $mountPoint
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mount $rootDisk $mountPoint
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# Create the swapspace without turning it on.
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mkswap -U ${swapUUID} -L ${swapLabel} /dev/vda${swapPartition}
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swapon /dev/vda${swapPartition}
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# Install a configuration.nix
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mkdir -p /mnt/etc/nixos
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${lib.optionalString (configFile != null) ''
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cp ${configFile} /mnt/etc/nixos/configuration.nix
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''}
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${lib.optionalString installBootLoader ''
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# In this throwaway resource, we only have `/dev/vda`, but the actual VM
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# may refer to another disk for bootloader, e.g. `/dev/vdb`. Use this
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# option to create a symlink from vda to any arbitrary device you want.
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${lib.optionalString (
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config.boot.loader.grub.enable &&
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config.boot.loader.grub.device != "/dev/vda"
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) ''
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mkdir -p $(dirname ${config.boot.loader.grub.device})
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ln -s /dev/vda ${config.boot.loader.grub.device}
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''}
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# Set up core system link, bootloader (sd-boot, GRUB, uboot, etc.), etc.
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NIXOS_INSTALL_BOOTLOADER=1 nixos-enter --root $mountPoint -- \
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/nix/var/nix/profiles/system/bin/switch-to-configuration boot
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# The above scripts will generate a random machine-id and we don't want
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# to bake a single ID into all our images.
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rm -f $mountPoint/etc/machine-id
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''}
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umount -R /mnt
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# Make sure resize2fs works. Note that resize2fs has stricter criteria for
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# resizing than a normal mount, so the `-c 0` and `-i 0` don't affect it.
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# Setting it to `now` doesn't produce deterministic output, of course, but
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# we can fix that when/if we start making images deterministic. This is
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# fixed to 1970-01-01 (UNIX timestamp 0). This two-step approach is
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# necessary otherwise `tune2fs` will want a fresher filesystem to perform
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# some changes.
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tune2fs -T now -U ${rootFSUID} -c 0 -i 0 $rootDisk
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tune2fs -f -T 19700101 $rootDisk
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''
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);
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in
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buildImage
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