nixpkgs/nixos/lib/make-btrfs-fs.nix

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# Builds an btrfs image containing a populated /nix/store with the closure
# of store paths passed in the storePaths parameter, in addition to the
# contents of a directory that can be populated with commands. The
# generated image is sized to only fit its contents, with the expectation
# that a script resizes the filesystem at boot time.
{ pkgs
, lib
# List of derivations to be included
, storePaths
# Whether or not to compress the resulting image with zstd
, compressImage ? false, zstd
# Shell commands to populate the ./files directory.
# All files in that directory are copied to the root of the FS.
, populateImageCommands ? ""
, volumeLabel
, uuid ? "44444444-4444-4444-8888-888888888888"
, btrfs-progs
, libfaketime
, fakeroot
}:
let
sdClosureInfo = pkgs.buildPackages.closureInfo { rootPaths = storePaths; };
in
pkgs.stdenv.mkDerivation {
name = "btrfs-fs.img${lib.optionalString compressImage ".zst"}";
nativeBuildInputs = [ btrfs-progs libfaketime fakeroot ] ++ lib.optional compressImage zstd;
buildCommand =
''
${if compressImage then "img=temp.img" else "img=$out"}
set -x
(
mkdir -p ./files
${populateImageCommands}
)
mkdir -p ./rootImage/nix/store
xargs -I % cp -a --reflink=auto % -t ./rootImage/nix/store/ < ${sdClosureInfo}/store-paths
(
GLOBIGNORE=".:.."
shopt -u dotglob
for f in ./files/*; do
cp -a --reflink=auto -t ./rootImage/ "$f"
done
)
cp ${sdClosureInfo}/registration ./rootImage/nix-path-registration
touch $img
faketime -f "1970-01-01 00:00:01" fakeroot mkfs.btrfs -L ${volumeLabel} -U ${uuid} -r ./rootImage --shrink $img
if ! btrfs check $img; then
echo "--- 'btrfs check' failed for BTRFS image ---"
return 1
fi
if [ ${builtins.toString compressImage} ]; then
echo "Compressing image"
zstd -v --no-progress ./$img -o $out
fi
'';
}