Add support for running the final make_image step in parallel

to make best use of larger machines with SSD storage. Use
PARALLEL_MAKE_IMAGE=<n> to specify how many to build in parallel.

CONF.sh

@@ -439,6 +439,11 @@ if [ -d "/etc/ssl/ca-debian" ]; then
 fi
 export WGET="wget $WGET_OPTS"
 
+# Run the make_image step in parallel? Specify the number of calls to
+# use in parallel here if desired. Don't go too high - this *will*
+# thrash your IO!
+#export PARALLEL_MAKE_IMAGE=4
+
 # Set this to force the Release file(s) to say "stable". Used in first
 # Etch builds to allow us to build before the archive updated
 #EARLY_BUILD_HACK=1

Makefile

@@ -497,6 +497,12 @@ image-trees: ok genlist
 images: ok $(OUT) $(BDIR)/checksum-check
 	$(Q)$(make_image) "$(BDIR)" "$(ARCHES)" "$(OUT)" "$(DEBVERSION)" "$(MIRROR)" "$(MKISOFS)" "$(MKISOFS_OPTS)" "$(JIGDO_OPTS)" "$(jigdo_cleanup)"
 
+parallel_images: $(subst volid,image,$(notdir $(wildcard $(BDIR)/*.volid)))
+	echo $^
+
+%.image: ok $(OUT) $(BDIR)/checksum-check
+	$(Q)CD=$(subst .image,,$@) $(make_image)  "$(BDIR)" "$(ARCHES)" "$(OUT)" "$(DEBVERSION)" "$(MIRROR)" "$(MKISOFS)" "$(MKISOFS_OPTS)" "$(JIGDO_OPTS)" "$(jigdo_cleanup)"
+
 check-number-given:
 	@test -n "$(CD)" || (echo "Give me a CD=<num> parameter !" && false)
 

build.sh

@@ -80,7 +80,12 @@ else
 fi
 echo "Building $NUMJIGDOS jigdos and $NUMISOS isos for $ARCHES $DISKTYPE"
 
-make $IMAGETARGET
+if [ "$IMAGETARGET" = "official_images" ] && [ ! -z "$PARALLEL_MAKE_IMAGE" ]; then
+    make ok init packagelists image-trees
+    make -j $PARALLEL_MAKE_IMAGE parallel_images
+else
+    make $IMAGETARGET
+fi
 
 if [ "$IMAGESUMS"x = 1x ]; then
 	make imagesums

debian/changelog

@@ -1,8 +1,14 @@
 debian-cd (3.1.32) UNRELEASED; urgency=medium
 
+  [ Holger Levsen ]
   * Update standards version to 4.5.1, no changes needed.
 
- -- Holger Levsen <holger@debian.org>  Thu, 19 Nov 2020 11:24:03 +0100
+  [ Steve McIntyre ]
+  * Add support for running the final make_image step in parallel to
+    make best use of larger machines with SSD storage. Use
+    PARALLEL_MAKE_IMAGE=<n> to specify how many to build in parallel.
+
+ -- Steve McIntyre <93sam@debian.org>  sat, 12 Dec 2020 03:12:36 +0100
 
 debian-cd (3.1.31) unstable; urgency=medium