sdk: track files with git and use it to implement proper clean targets

Initialize a Git repository in the SDK and use git reset / git clean
to rollback any SDK changes with "make clean" or "make dirclean".

This approach is more robust than nuking entire directory trees because
some parts of them might have been shipped with the original archive.

Signed-off-by: Jo-Philipp Wich <jow@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@43904 3c298f89-4303-0410-b956-a3cf2f4a3e73

include/toplevel.mk

@@ -135,7 +135,7 @@ kernel_menuconfig: prepare_kernel_conf
 kernel_nconfig: prepare_kernel_conf
 	$(_SINGLE)$(NO_TRACE_MAKE) -C target/linux nconfig
 
-tmp/.prereq-build: include/prereq-build.mk
+tmp/.prereq-build: $(if $(SDK),.git/config) include/prereq-build.mk
 	mkdir -p tmp
 	rm -f tmp/.host.mk
 	@$(_SINGLE)$(NO_TRACE_MAKE) -j1 -r -s -f $(TOPDIR)/include/prereq-build.mk prereq 2>/dev/null || { \

target/sdk/files/Makefile

@@ -14,6 +14,16 @@ export TOPDIR LC_ALL LANG SDK
 
 world:
 
+# Initialize SDK snapshot
+.git/config:
+	@( \
+		echo -n "Initializing SDK ... "; \
+		git init -q .; \
+		find . -mindepth 1 -maxdepth 1 -not -name feeds | xargs git add; \
+		git commit -q -m "Initial state"; \
+		echo "ok."; \
+	)
+
 include $(TOPDIR)/include/host.mk
 
 ifneq ($(OPENWRT_BUILD),1)
@@ -36,14 +46,17 @@ else
 $(package/stamp-compile): $(BUILD_DIR)/.prepared
 $(BUILD_DIR)/.prepared: Makefile
 	@mkdir -p $$(dirname $@)
-	@mkdir -p bin/packages
 	@touch $@
 
 clean: FORCE
-	rm -rf $(BUILD_DIR) $(BIN_DIR)
+	git clean -f -d $(STAGING_DIR); true
+	git clean -f -d $(BUILD_DIR); true
+	git clean -f -d $(BIN_DIR); true
 
 dirclean: clean
-	rm -rf $(TMP_DIR)
+	git reset --hard HEAD
+	git clean -f -d
+	rm -rf feeds/
 
 # check prerequisites before starting to build
 prereq: $(package/stamp-prereq) ;