hooks/eatmydata: download instead of copy-ing from host

hooks/eatmydata/README.txt

@@ -0,0 +1,5 @@
+Adding this directory with --hook-directory will result in mmdebstrap using
+dpkg inside an eatmydata wrapper script. This will result in spead-ups on
+systems where sync() takes some time. Using --dpkgopt=force-unsafe-io will have
+a lesser effect compared to eatmydata. See:
+https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=613428

hooks/eatmydata/customize.sh

@@ -4,7 +4,22 @@ set -exu
 
 rootdir="$1"
 
-rm "$rootdir/usr/bin/eatmydata"
+if [ -e "$rootdir/var/lib/dpkg/arch" ]; then
+	chrootarch=$(head -1 "$rootdir/var/lib/dpkg/arch")
+else
+	chrootarch=$(dpkg --print-architecture)
+fi
+libdir="/usr/lib/$(dpkg-architecture -a $chrootarch -q DEB_HOST_MULTIARCH)"
+
+# if eatmydata was actually installed properly, then we are not removing
+# anything here
+if ! chroot "$rootdir" dpkg-query --list eatmydata; then
+	rm "$rootdir/usr/bin/eatmydata"
+fi
+if ! chroot "$rootdir" dpkg-query --list libeatmydata1; then
+	rm "$rootdir$libdir"/libeatmydata.so*
+fi
+
 mv "$rootdir/usr/bin/dpkg.orig" "$rootdir/usr/bin/dpkg"
 
 sync

hooks/eatmydata/extract.sh

@@ -4,10 +4,57 @@ set -exu
 
 rootdir="$1"
 
-libdir="/usr/lib/$(dpkg-architecture -q DEB_HOST_MULTIARCH)"
-mkdir -p "$rootdir$libdir"
-cp -a $libdir/libeatmydata* "$rootdir$libdir"
-cp -a /usr/bin/eatmydata "$rootdir/usr/bin"
+if [ -e "$rootdir/var/lib/dpkg/arch" ]; then
+	chrootarch=$(head -1 "$rootdir/var/lib/dpkg/arch")
+else
+	chrootarch=$(dpkg --print-architecture)
+fi
+
+eval $(apt-config shell trusted Dir::Etc::trusted/f)
+eval $(apt-config shell trustedparts Dir::Etc::trustedparts/d)
+tmpfile=$(mktemp --tmpdir="$rootdir/tmp")
+cat << END > "$tmpfile"
+Apt::Architecture "$chrootarch";
+Apt::Architectures "$chrootarch";
+Dir "$rootdir";
+Dir::Etc::Trusted "$trusted";
+Dir::Etc::TrustedParts "$trustedparts";
+END
+# we run "apt-get download --print-uris" in a temporary directory, to make sure
+# that the packages do not already exist in the current directory, or otherwise
+# nothing will be printed for them
+tmpdir=$(mktemp --directory --tmpdir="$rootdir/tmp")
+env --chdir="$tmpdir" APT_CONFIG="$tmpfile" apt-get download --print-uris eatmydata libeatmydata1 \
+	| sed -ne "s/^'\([^']\+\)'\s\+\([^\s]\+\)\s\+\([0-9]\+\)\s\+\(SHA256:[a-f0-9]\+\)$/\1 \2 \3 \4/p" \
+	| while read uri fname size hash; do
+		echo "processing $fname" >&2
+		if [ -e "$tmpdir/$fname" ]; then
+			echo "$tmpdir/$fname already exists" >&2
+			exit 1
+		fi
+		env --chdir="$tmpdir" APT_CONFIG="$tmpfile" /usr/lib/apt/apt-helper download-file "$uri" "$fname" Checksum-FileSize:"$size" "$hash"
+		case "$fname" in
+			eatmydata_*_all.deb)
+				mkdir -p "$rootdir/usr/bin"
+				dpkg-deb --fsys-tarfile "$tmpdir/$fname" \
+					| tar --directory="$rootdir/usr/bin" --strip-components=3 --extract --verbose ./usr/bin/eatmydata
+				;;
+			libeatmydata1_*_$chrootarch.deb)
+				libdir="/usr/lib/$(dpkg-architecture -a $chrootarch -q DEB_HOST_MULTIARCH)"
+				mkdir -p "$rootdir$libdir"
+				dpkg-deb --fsys-tarfile "$tmpdir/$fname" \
+					| tar --directory="$rootdir$libdir" --strip-components=4 --extract --verbose --wildcards ".$libdir/libeatmydata.so*"
+				;;
+			*)
+				echo "unexpected filename: $fname" >&2
+				exit 1
+				;;
+		esac
+		rm "$tmpdir/$fname"
+done
+rm "$tmpfile"
+rmdir "$tmpdir"
+
 mv "$rootdir/usr/bin/dpkg" "$rootdir/usr/bin/dpkg.orig"
 cat << END > "$rootdir/usr/bin/dpkg"
 #!/bin/sh