update-initramfs: use dpkg-trigger

This is a lightly modified version of Ian Jackson's original patch,
incorporating maximilian attems's comments.

dh_installdeb automatically installs the triggers file, so the rules file
does not need to be changed.

debian/initramfs-tools.postinst

@@ -6,9 +6,16 @@ if [ ! -e /etc/initramfs-tools/modules ]; then
 	cp /usr/share/initramfs-tools/modules /etc/initramfs-tools/
 fi
 
-# Regenerate initramfs on upgrade
-if [ "$1" = "configure" ] && [ -n "$2" ]; then
+# Regenerate initramfs whenever we go to dpkg state `installed'
+
+if [ "x$1" != xtriggered ] && \
+   dpkg --compare-versions "$DPKG_RUNNING_VERSION" ge '1.14.5ubuntu10~~'
+then
+	# this activates the trigger, if triggers are working
 	update-initramfs -u
+else
+	# force it to actually happen
+	DPKG_MAINTSCRIPT_PACKAGE='' update-initramfs -u
 fi
 
 #DEBHELPER#

debian/initramfs-tools.triggers

@@ -0,0 +1 @@
+interest update-initramfs

update-initramfs

@@ -4,6 +4,7 @@ STATEDIR=/var/lib/initramfs-tools
 BOOTDIR=/boot
 CONF=/etc/initramfs-tools/update-initramfs.conf
 KPKGCONF=/etc/kernel-img.conf
+USETRIGGERS=true
 mode=""
 version=""
 
@@ -11,6 +12,18 @@ set -e
 
 [ -r ${CONF} ] && . ${CONF}
 
+if	   $USETRIGGERS						\
+	&& [ x"$DPKG_MAINTSCRIPT_PACKAGE" != x ]		\
+	&& [ $# = 1 ]	 					\
+	&& [ x"$1" = x-u ]					\
+	&& dpkg-trigger --check-supported 2>/dev/null
+then
+	if dpkg-trigger --no-await update-initramfs; then
+		echo "update-initramfs: deferring update (trigger activated)"
+		exit 0
+	fi
+fi
+
 usage()
 {
 	if [ -n "${1}" ]; then