hooks: Add resume hook instead of hardcoding RESUME once on preinst

This logic is better run every time on update-initramfs,
as swap partition of a system might change.
Also there are scenarios where the preinstall picks up
a wrong value that stays wrongly hardcoded.
This results in a 5s useless wait on boot.

The biggest swap partition is used as valid guess.
This was previously the logic and is the logic used by ubiquity
(Ubuntu live installer) too.

Closes: #565225, LP 50437.

Thanks-to: Dmitrijs Ledkovs <launchpad@surgut.co.uk>
Reviewed-by: Martin Pitt <martin.pitt@ubuntu.com>
Reviewed-by: Michael Prokop <mika@debian.org>
Signed-off-by: maximilian attems <maks@debian.org>

debian/initramfs-tools.preinst

-#!/bin/sh
-
-set -e
-
-chrooted() {
-	# borrowed from udev's postinst
-	if [ "$(stat -c %d/%i /)" = "$(stat -Lc %d/%i /proc/1/root 2>/dev/null)" ]; then
-		# the devicenumber/inode pair of / is the same as that of
-		# /sbin/init's root, so we're *not* in a chroot and hence
-		# return false.
-		return 1
-	fi
-	return 0
-}
-
-case "$1" in
-	install)
-		mkdir -p /etc/initramfs-tools/conf.d
-
-		# First time install.  Can we autodetect the RESUME partition?
-		if [ -r /proc/swaps ]; then
-			RESUME=$(grep ^/dev/ /proc/swaps | sort -rk3 \
-				| head -n 1 | cut -d " " -f 1)
-			if command -v blkid >/dev/null 2>&1; then
-				UUID=$(blkid -s UUID -o value "$RESUME" || true)
-			# FIXME: post-Wheezy remove vol_id invocations
-			elif command -v vol_id >/dev/null 2>&1; then
-				UUID=$(vol_id -u "$RESUME" || true)
-			elif [ -x /lib/udev/vol_id ]; then
-				UUID=$(/lib/udev/vol_id -u "$RESUME" || true)
-			fi
-			if [ -n "$UUID" ]; then
-				RESUME="UUID=$UUID"
-			fi
-		fi
-
-		# write conf.d/resume if not in a chroot
-		if [ -n "${RESUME}" ] && ! chrooted; then
-			echo "RESUME=${RESUME}" > /etc/initramfs-tools/conf.d/resume
-		fi
-
-	;;
-esac
-
-#DEBHELPER#

hooks/resume

+#!/bin/sh
+
+PREREQ=""
+
+prereqs()
+{
+	echo "$PREREQ"
+}
+
+case $1 in
+# get pre-requisites
+prereqs)
+	prereqs
+	exit 0
+	;;
+esac
+
+# we need to be able to read the listed swap partitions
+if [ ! -r /proc/swaps ]; then
+	exit 0
+fi
+
+# borrowed from udev's postinst
+chrooted() {
+	if [ "$(stat -c %d/%i /)" = "$(stat -Lc %d/%i /proc/1/root 2>/dev/null)" ]; then
+		# the devicenumber/inode pair of / is the same as that of
+		# /sbin/init's root, so we're *not* in a chroot and hence
+		# return false.
+		return 1
+	fi
+	return 0
+}
+
+
+# Try to autodetect the RESUME partition, using biggest swap?
+RESUME=$(grep ^/dev/ /proc/swaps | sort -rk3 | head -n 1 | cut -d " " -f 1)
+if command -v blkid >/dev/null 2>&1; then
+	UUID=$(blkid -s UUID -o value "$RESUME" || true)
+	if [ -n "$UUID" ]; then
+			RESUME="UUID=$UUID"
+	fi
+fi
+
+# write conf.d/resume if not in a chroot
+if [ -n "${RESUME}" ] && !chrooted; then
+	echo "RESUME=${RESUME}" > ${DESTDIR}/conf/conf.d/resume
+fi