Simplify firmware variant selection

Instead of tampering with the 'DEFAULT' property of meta packages on
every build in a non-portable way, use the build system as intended and
select packages using an approriate build config ('.config').

This is achived by adding the approriate variant package to the build
config before expanding it using defconfig.

By that, the fff-variant-* packages and FFF_VARIANT environment variable
can be removed. Base packages required in both variants are now included
via fff-base (formerly fff-variant/default).

Besides cleaning up the build process, this change also fixes a recent
issue with build dependencies, as they are evaluated on a per-package
basis instead of per-variant. Due to that, dependencies of all
variants are compiled, regardless of the selected variant. Combined with
a recent build issue of mosquitto (see [1]), the node variant could not
be built from a clean state.

[1] https://github.com/eclipse/mosquitto/issues/2432

Signed-off-by: Fabian Bläse <fabian@blaese.de>

buildscript

@@ -126,20 +126,9 @@ prepare() {
 
     patch_target
 
-    # apply variant to ensure the included file "variant.mk"
-    # exists in builddir.
-    apply_variant
-
     update_feeds
 }
 
-apply_variant() {
-    # set the variant for this build
-    export FFF_VARIANT=$(cat selected_variant)
-    # force the reevaluation of this Makefile to make note of the new variant
-    touch ./src/packages/fff/fff/Makefile
-}
-
 update_feeds() {
     ## generate own feeds.conf
     #this local variable should be globally configure variable used in get_source and here
@@ -174,8 +163,6 @@ update_feeds() {
 }
 
 prebuild() {
-    apply_variant
-
     #create filesdir for our config
     /bin/rm -rf "$builddir"/files
     mkdir "$builddir"/files
@@ -193,6 +180,9 @@ prebuild() {
         version="$variant-$version"
     fi
 
+    # select variant packages
+    echo "CONFIG_PACKAGE_fff-${variant}=y" >> "$builddir"/.config
+
     {
         echo "FIRMWARE_VERSION=\"$version\""
         echo "VARIANT=\"$variant\""

src/packages/fff/fff-base/Makefile

@@ -0,0 +1,34 @@
+include $(TOPDIR)/rules.mk
+
+PKG_NAME:=fff-base
+PKG_RELEASE:=$(COMMITCOUNT)
+
+include $(INCLUDE_DIR)/package.mk
+
+define Package/fff-base
+	SECTION:=base
+	CATEGORY:=Freifunk
+	TITLE:=Freifunk-Franken base dependencies
+	URL:=https://www.freifunk-franken.de
+	DEFAULT:=y
+	DEPENDS:= \
+		+iptables \
+		+ip6tables \
+		+micrond \
+		+odhcp6c \
+		+fff-config \
+		+fff-network \
+		+fff-nodewatcher \
+		+fff-simple-tc \
+		+fff-support \
+		+fff-sysupgrade \
+		+fff-timeserver \
+		+fff-web-ui \
+		+fff-wireless
+endef
+
+define Package/fff-variant/description
+	This package includes base packages used in the Freifunk-Franken firmware
+endef
+
+$(eval $(call BuildPackage,fff-base))

src/packages/fff/fff/Makefile

@@ -1,56 +0,0 @@
-include $(TOPDIR)/rules.mk
-
-PKG_NAME:=fff
-PKG_RELEASE:=$(COMMITCOUNT)
-
-include $(INCLUDE_DIR)/package.mk
-
-define Package/fff-variant/default
-	SECTION:=base
-	CATEGORY:=Freifunk
-	URL:=https://www.freifunk-franken.de
-	DEFAULT:=$(if $(filter fff-variant-$(FFF_VARIANT),$(1)),y,n)
-	DEPENDS:= \
-		+iptables \
-		+ip6tables \
-		+micrond \
-		+odhcp6c \
-		+fff-config \
-		+fff-network \
-		+fff-nodewatcher \
-		+fff-simple-tc \
-		+fff-support \
-		+fff-sysupgrade \
-		+fff-timeserver \
-		+fff-web-ui \
-		+fff-wireless
-endef
-
-define Package/fff-variant/default/description
-	This package is used to switch one of the variants on by default
-endef
-
-define Package/fff-variant-layer3
-	$(Package/fff-variant/default)
-	TITLE:=Freifunk-Franken Layer3 Variant
-	DEPENDS+=+fff-layer3
-	VARIANT:=layer3
-endef
-
-define Package/fff-variant-layer3/description
-	$(Package/fff-variant/default/description)
-endef
-
-define Package/fff-variant-node
-	$(Package/fff-variant/default)
-	TITLE:=Freifunk-Franken Node Variant
-	DEPENDS+=+fff-node
-	VARIANT:=node
-endef
-
-define Package/fff-variant-node/description
-	$(Package/fff-variant/default/description)
-endef
-
-$(eval $(call BuildPackage,fff-variant-layer3))
-$(eval $(call BuildPackage,fff-variant-node))