diff options
Diffstat (limited to 'nixos/lib/make-ext4-fs.nix')
-rw-r--r-- | nixos/lib/make-ext4-fs.nix | 86 |
1 files changed, 86 insertions, 0 deletions
diff --git a/nixos/lib/make-ext4-fs.nix b/nixos/lib/make-ext4-fs.nix new file mode 100644 index 00000000000..416beeb32f2 --- /dev/null +++ b/nixos/lib/make-ext4-fs.nix @@ -0,0 +1,86 @@ +# Builds an ext4 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" +, e2fsprogs +, libfaketime +, perl +, fakeroot +}: + +let + sdClosureInfo = pkgs.buildPackages.closureInfo { rootPaths = storePaths; }; +in +pkgs.stdenv.mkDerivation { + name = "ext4-fs.img${lib.optionalString compressImage ".zst"}"; + + nativeBuildInputs = [ e2fsprogs.bin libfaketime perl fakeroot ] + ++ lib.optional compressImage zstd; + + buildCommand = + '' + ${if compressImage then "img=temp.img" else "img=$out"} + ( + mkdir -p ./files + ${populateImageCommands} + ) + + echo "Preparing store paths for image..." + + # Create nix/store before copying path + 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 + ) + + # Also include a manifest of the closures in a format suitable for nix-store --load-db + cp ${sdClosureInfo}/registration ./rootImage/nix-path-registration + + # Make a crude approximation of the size of the target image. + # If the script starts failing, increase the fudge factors here. + numInodes=$(find ./rootImage | wc -l) + numDataBlocks=$(du -s -c -B 4096 --apparent-size ./rootImage | tail -1 | awk '{ print int($1 * 1.10) }') + bytes=$((2 * 4096 * $numInodes + 4096 * $numDataBlocks)) + echo "Creating an EXT4 image of $bytes bytes (numInodes=$numInodes, numDataBlocks=$numDataBlocks)" + + truncate -s $bytes $img + + faketime -f "1970-01-01 00:00:01" fakeroot mkfs.ext4 -L ${volumeLabel} -U ${uuid} -d ./rootImage $img + + export EXT2FS_NO_MTAB_OK=yes + # I have ended up with corrupted images sometimes, I suspect that happens when the build machine's disk gets full during the build. + if ! fsck.ext4 -n -f $img; then + echo "--- Fsck failed for EXT4 image of $bytes bytes (numInodes=$numInodes, numDataBlocks=$numDataBlocks) ---" + cat errorlog + return 1 + fi + + # We may want to shrink the file system and resize the image to + # get rid of the unnecessary slack here--but see + # https://github.com/NixOS/nixpkgs/issues/125121 for caveats. + + if [ ${builtins.toString compressImage} ]; then + echo "Compressing image" + zstd -v --no-progress ./$img -o $out + fi + ''; +} |