add jessie-or-older extract hook

coverage.txt

@@ -354,3 +354,7 @@ Needs-QEMU: true
 Test: pivot_root
 Modes: root unshare
 Needs-QEMU: true
+
+Test: jessie-or-older
+Needs-QEMU: true
+Variants: essential apt minbase

hooks/jessie-or-older/extract00.sh

@@ -0,0 +1,48 @@
+#!/bin/sh
+
+set -eu
+
+if [ "${MMDEBSTRAP_VERBOSITY:-1}" -ge 3 ]; then
+	set -x
+fi
+
+TARGET="$1"
+
+for f in available diversions cmethopt; do
+	if [ ! -e "$TARGET/var/lib/dpkg/$f" ]; then
+		touch "$TARGET/var/lib/dpkg/$f"
+	fi
+done
+
+if [ -z "${MMDEBSTRAP_ESSENTIAL+x}" ]; then
+	MMDEBSTRAP_ESSENTIAL=
+	for f in "$TARGET/var/cache/apt/archives/"*.deb; do
+		[ -f "$f" ] || continue
+		f="${f#"$TARGET"}"
+		MMDEBSTRAP_ESSENTIAL="$MMDEBSTRAP_ESSENTIAL $f"
+	done
+fi
+
+fname_base_passwd=
+fname_base_files=
+fname_dpkg=
+for pkg in $MMDEBSTRAP_ESSENTIAL; do
+	pkgname=$(dpkg-deb --show --showformat='${Package}' "$TARGET/$pkg")
+	# shellcheck disable=SC2034
+	case $pkgname in
+		base-passwd) fname_base_passwd=$pkg;;
+		base-files)  fname_base_files=$pkg;;
+		dpkg)        fname_dpkg=$pkg;;
+	esac
+done
+
+for var in base_passwd base_files dpkg; do
+	eval 'val=$fname_'"$var"
+	[ -z "$val" ] && continue
+	chroot "$TARGET" dpkg --install --force-depends "$val"
+done
+
+# shellcheck disable=SC2086
+chroot "$TARGET" dpkg --unpack --force-depends $MMDEBSTRAP_ESSENTIAL
+
+chroot "$TARGET" dpkg --configure --pending

mmdebstrap

@@ -1543,6 +1543,7 @@ sub setup_mounts {
 sub run_hooks {
     my $name           = shift;
     my $options        = shift;
+    my $essential_pkgs = shift;
 
     if (scalar @{ $options->{"${name}_hook"} } == 0) {
         return;
@@ -1601,6 +1602,12 @@ sub run_hooks {
         push @env_opts,
           ("MMDEBSTRAP_INCLUDE=" . (join ",", @escaped_includes));
     }
+    # Give the extract hook access to the essential packages that are about to
+    # be installed
+    if ($name eq "extract" and scalar @{$essential_pkgs} > 0) {
+        push @env_opts,
+          ("MMDEBSTRAP_ESSENTIAL=" . (join " ", @{$essential_pkgs}));
+    }
 
     # Unset the close-on-exec flag, so that the file descriptor does not
     # get closed when we exec

tests/jessie-or-older

@@ -0,0 +1,39 @@
+#!/bin/sh
+set -eu
+export LC_ALL=C.UTF-8
+if [ ! -e /mmdebstrap-testenv ]; then
+	echo "this test modifies the system and should only be run inside a container" >&2
+	exit 1
+fi
+adduser --gecos user --disabled-password user
+sysctl -w kernel.unprivileged_userns_clone=1
+export SOURCE_DATE_EPOCH={{ SOURCE_DATE_EPOCH }}
+
+filter() {
+	./tarfilter \
+		--path-exclude=/usr/bin/uncompress \
+		--path-exclude=/var/cache/debconf/config.dat-old \
+		--path-exclude=/var/cache/debconf/templates.dat-old \
+		--path-exclude=/var/lib/dpkg/available \
+		--path-exclude=/var/lib/dpkg/cmethopt \
+		--path-exclude=/var/lib/dpkg/status-old \
+		--path-exclude=/var/lib/shells.state
+}
+
+# base for comparison without jessie-or-older hook
+{{ CMD }} --mode=root --variant={{ VARIANT }} {{ DIST }} - {{ MIRROR }} | filter > /tmp/debian-chroot-root-normal.tar
+
+# root
+{{ CMD }} --mode=root --variant={{ VARIANT }} --hook-dir=./hooks/jessie-or-older {{ DIST }} - {{ MIRROR }} | filter > /tmp/debian-chroot-root.tar
+cmp /tmp/debian-chroot-root-normal.tar /tmp/debian-chroot-root.tar
+rm /tmp/debian-chroot-root.tar
+# unshare
+runuser -u user -- {{ CMD }} --mode=unshare --variant={{ VARIANT }} --hook-dir=./hooks/jessie-or-older {{ DIST }} - {{ MIRROR }} | filter > /tmp/debian-chroot-unshare.tar
+cmp /tmp/debian-chroot-root-normal.tar /tmp/debian-chroot-unshare.tar
+rm /tmp/debian-chroot-unshare.tar
+# fakechroot
+runuser -u user -- {{ CMD }} --mode=fakechroot --variant={{ VARIANT }} --hook-dir=./hooks/jessie-or-older {{ DIST }} - {{ MIRROR }} | filter > /tmp/debian-chroot-fakechroot.tar
+cmp /tmp/debian-chroot-root-normal.tar /tmp/debian-chroot-fakechroot.tar
+rm /tmp/debian-chroot-fakechroot.tar
+
+rm /tmp/debian-chroot-root-normal.tar