487be791d7
exportReferencesGraph is deprecated and doesn't have the generated initial Nix database contain the SHA256 of the contents of the store paths, which breaks various things under Nix 2.0.
87 lines
3.5 KiB
Nix
87 lines
3.5 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. The generated image
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# is sized to only fit its contents, with the expectation that a script
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# resizes the filesystem at boot time.
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{ pkgs
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, storePaths
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, volumeLabel
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}:
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let
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sdClosureInfo = pkgs.closureInfo { rootPaths = storePaths; };
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in
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pkgs.stdenv.mkDerivation {
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name = "ext4-fs.img";
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nativeBuildInputs = with pkgs; [e2fsprogs libfaketime perl];
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buildCommand =
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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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# Also include a manifest of the closures in a format suitable for nix-store --load-db.
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cp ${sdClosureInfo}/registration nix-path-registration
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# Make a crude approximation of the size of the target image.
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# If the script starts failing, increase the fudge factors here.
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numInodes=$(find $storePaths | wc -l)
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numDataBlocks=$(du -c -B 4096 --apparent-size $storePaths | awk '$2 == "total" { 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 $out
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faketime -f "1970-01-01 00:00:01" mkfs.ext4 -L ${volumeLabel} -U 44444444-4444-4444-8888-888888888888 $out
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# Populate the image contents by piping a bunch of commands to the `debugfs` tool from e2fsprogs.
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# For example, to copy /nix/store/abcd...efg-coreutils-8.23/bin/sleep:
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# cd /nix/store/abcd...efg-coreutils-8.23/bin
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# write /nix/store/abcd...efg-coreutils-8.23/bin/sleep sleep
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# sif sleep mode 040555
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# sif sleep gid 30000
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# In particular, debugfs doesn't handle absolute target paths; you have to 'cd' in the virtual
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# filesystem first. Likewise the intermediate directories must already exist (using `find`
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# handles that for us). And when setting the file's permissions, the inode type flags (__S_IFDIR,
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# __S_IFREG) need to be set as well.
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(
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echo write nix-path-registration nix-path-registration
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echo mkdir nix
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echo cd /nix
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echo mkdir store
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# XXX: This explodes in exciting ways if anything in /nix/store has a space in it.
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find $storePaths -printf '%y %f %h %m\n'| while read -r type file dir perms; do
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# echo "TYPE=$type DIR=$dir FILE=$file PERMS=$perms" >&2
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echo "cd $dir"
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case $type in
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d)
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echo "mkdir $file"
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echo sif $file mode $((040000 | 0$perms)) # magic constant is __S_IFDIR
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;;
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f)
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echo "write $dir/$file $file"
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echo sif $file mode $((0100000 | 0$perms)) # magic constant is __S_IFREG
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;;
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l)
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echo "symlink $file $(readlink "$dir/$file")"
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;;
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*)
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echo "Unknown entry: $type $dir $file $perms" >&2
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exit 1
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;;
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esac
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echo sif $file gid 30000 # chgrp to nixbld
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done
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) | faketime -f "1970-01-01 00:00:01" debugfs -w $out -f /dev/stdin > errorlog 2>&1
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# The debugfs tool doesn't terminate on error nor exit with a non-zero status. Check manually.
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if egrep -q 'Could not allocate|File not found' errorlog; then
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cat errorlog
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echo "--- Failed to create EXT4 image of $bytes bytes (numInodes=$numInodes, numDataBlocks=$numDataBlocks) ---"
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return 1
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fi
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'';
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}
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