add a way to prevent a layer (and descendants) from being made into a sqashfs

for the live server build, i want to make a layer to install the kernel
into but do not want the layer itself to be published.

the implementation is a bit clunky but it works.

live-build/auto/config

@@ -1023,6 +1023,9 @@ echo "IMAGEFORMAT=\"$IMAGEFORMAT\"" >> config/chroot
 if [ -n "$PASSES" ]; then
 	echo "PASSES=\"$PASSES\"" >> config/common
 fi
+if [ -n "$NO_SQUASHFS_PASSES" ]; then
+    echo "NO_SQUASHFS_PASSES=\"$NO_SQUASHFS_PASSES\"" >> config/common
+fi
 if [ -n "$LIVE_PASSES" ]; then
 	echo "LIVE_PASSES=\"$LIVE_PASSES\"" >> config/common
 fi

live-build/lb_binary_layered

@@ -92,6 +92,22 @@ build_layered_squashfs () {
 		rm -f chroot/boot/initrd.img-* chroot/boot/vmlinu{x,z}-*
 	fi
 
+        make_squashfs=yes
+        ppass="${pass}"
+        while :; do
+            for nsp in ${NO_SQUASHFS_PASSES}; do
+                if [ "${ppass}" = "${nsp}" ]; then
+                    make_squashfs=no
+                    break 2
+                fi
+            done
+            ppass="$(get_parent_pass "${ppass}")"
+            if [ -z "${ppass}" ]; then
+                break
+            fi
+        done
+
+        if [ $make_squashfs = yes ]; then
 		# Full manifest until that PASS
 		squashfs_f_manifest="${base}.manifest"
 		create_manifest "chroot" "${squashfs_f_manifest}.full"
@@ -121,7 +137,8 @@ build_layered_squashfs () {
 			cp "${squashfs_f_manifest}.full" "${prefix}.manifest"
 		fi
 
-	create_squashfs "overlay.${pass}" ${squashfs_f}
+		create_squashfs "overlay.${pass}/" ${squashfs_f}
+	fi
 
 	if [ -n "$lowerdirs" ]; then
 		umount chroot