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dockerTools: Support mounting images with more than 16 layers (backport to 24.11) #392435

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dockerTools: Support mounting images with more than 16 layers (backport to 24.11) #392435

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29 changes: 22 additions & 7 deletions pkgs/build-support/docker/default.nix
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Original file line number Diff line number Diff line change
Expand Up @@ -295,7 +295,7 @@ rec {
fi

# Unpack all of the parent layers into the image.
lowerdir=""
lowerdirs=()
extractionID=0
for layerTar in $(cat layer-list); do
echo "Unpacking layer $layerTar"
Expand All @@ -308,7 +308,7 @@ rec {
find image/$extractionID/layer -name ".wh.*" -exec bash -c 'name="$(basename {}|sed "s/^.wh.//")"; mknod "$(dirname {})/$name" c 0 0; rm {}' \;

# Get the next lower directory and continue the loop.
lowerdir=image/$extractionID/layer''${lowerdir:+:}$lowerdir
lowerdirs=( "image/$extractionID/layer" "''${lowerdirs[@]}" )
done

mkdir work
Expand All @@ -321,11 +321,25 @@ rec {
${preMount}
''}

if [ -n "$lowerdir" ]; then
mount -t overlay overlay -olowerdir=$lowerdir,workdir=work,upperdir=layer mnt
else
mount --bind layer mnt
fi
mountDirs() {
local IFS=:
declare -g layerNum
if [ "$#" -eq 0 ]; then
mount --bind layer mnt
return
elif [ "$#" -lt 16 ]; then
mount -t overlay overlay -olowerdir="$*",workdir=work,upperdir=layer mnt
return
fi

# tough case: we have too many layers to mount at once; recurse
: layerNum=''${layerNum:=0}
mkdir -p "work$layerNum" "layer$layerNum" "mnt$layerNum" || return
mount -t overlay overlay -o "lowerdir=''${*:1:16},workdir=work$layerNum,upperdir=layer$layerNum" "mnt$layerNum" || return
mountDirs "mnt$layerNum" "''${@:17}"
}

mountDirs "''${lowerdirs[@]}"

${lib.optionalString (postMount != "") ''
# Execute post-mount steps
Expand All @@ -350,6 +364,7 @@ rec {

postMount = ''
echo "Packing raw image..."
mkdir -p -- "$out"
tar -C mnt --hard-dereference --sort=name --mtime="@$SOURCE_DATE_EPOCH" -cf $out/layer.tar .
'';

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