100 lines
3.6 KiB
Nix
100 lines
3.6 KiB
Nix
# Builds an ext4 image containing a populated /nix/store with the closure
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# of store paths passed in the storePaths parameter, in addition to the
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# contents of a directory that can be populated with commands. The
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# generated image is sized to only fit its contents, with the expectation
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# that a script resizes the filesystem at boot time.
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{ pkgs
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, lib
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# List of derivations to be included
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, storePaths
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# Whether or not to compress the resulting image with zstd
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, compressImage ? false, zstd
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# Shell commands to populate the ./files directory.
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# All files in that directory are copied to the root of the FS.
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, populateImageCommands ? ""
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, volumeLabel
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, uuid ? "44444444-4444-4444-8888-888888888888"
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, e2fsprogs
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, libfaketime
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, perl
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, lkl
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}:
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let
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sdClosureInfo = pkgs.buildPackages.closureInfo { rootPaths = storePaths; };
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in
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pkgs.stdenv.mkDerivation {
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name = "ext4-fs.img${lib.optionalString compressImage ".zst"}";
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nativeBuildInputs = [ e2fsprogs.bin libfaketime perl lkl ]
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++ lib.optional compressImage zstd;
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buildCommand =
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''
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${if compressImage then "img=temp.img" else "img=$out"}
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(
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mkdir -p ./files
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${populateImageCommands}
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)
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# Add the closures of the top-level store objects.
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storePaths=$(cat ${sdClosureInfo}/store-paths)
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# Make a crude approximation of the size of the target image.
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# If the script starts failing, increase the fudge factors here.
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numInodes=$(find $storePaths ./files | wc -l)
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numDataBlocks=$(du -s -c -B 4096 --apparent-size $storePaths ./files | tail -1 | awk '{ print int($1 * 1.03) }')
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bytes=$((2 * 4096 * $numInodes + 4096 * $numDataBlocks))
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echo "Creating an EXT4 image of $bytes bytes (numInodes=$numInodes, numDataBlocks=$numDataBlocks)"
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truncate -s $bytes $img
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faketime -f "1970-01-01 00:00:01" mkfs.ext4 -L ${volumeLabel} -U ${uuid} $img
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# Also include a manifest of the closures in a format suitable for nix-store --load-db.
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cp ${sdClosureInfo}/registration nix-path-registration
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cptofs -t ext4 -i $img nix-path-registration /
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# Create nix/store before copying paths
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faketime -f "1970-01-01 00:00:01" mkdir -p nix/store
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cptofs -t ext4 -i $img nix /
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echo "copying store paths to image..."
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cptofs -t ext4 -i $img $storePaths /nix/store/
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echo "copying files to image..."
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cptofs -t ext4 -i $img ./files/* /
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# I have ended up with corrupted images sometimes, I suspect that happens when the build machine's disk gets full during the build.
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if ! fsck.ext4 -n -f $img; then
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echo "--- Fsck failed for EXT4 image of $bytes bytes (numInodes=$numInodes, numDataBlocks=$numDataBlocks) ---"
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cat errorlog
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return 1
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fi
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(
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# Resizes **snugly** to its actual limits (or closer to)
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free=$(dumpe2fs $img | grep '^Free blocks:')
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blocksize=$(dumpe2fs $img | grep '^Block size:')
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blocks=$(dumpe2fs $img | grep '^Block count:')
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blocks=$((''${blocks##*:})) # format the number.
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blocksize=$((''${blocksize##*:})) # format the number.
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# System can't boot with 0 blocks free.
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# Add 16MiB of free space
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fudge=$(( 16 * 1024 * 1024 / blocksize ))
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size=$(( blocks - ''${free##*:} + fudge ))
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echo "Resizing from $blocks blocks to $size blocks. (~ $((size*blocksize/1024/1024))MiB)"
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EXT2FS_NO_MTAB_OK=yes resize2fs $img -f $size
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)
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# And a final fsck, because of the previous truncating.
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fsck.ext4 -n -f $img
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if [ ${builtins.toString compressImage} ]; then
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echo "Compressing image"
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zstd -v --no-progress ./$img -o $out
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fi
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'';
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}
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