Facilitate saving of configuration files for board developers

@@ -163,6 +163,13 @@
 	$(MAKE) $(LINUX26_MAKE_FLAGS) -C $(LINUX26_DIR) \
 		$(subst linux-,,$(subst linux26-,,$@))
 
+ifeq ($(BR2_LINUX_KERNEL_USE_CUSTOM_CONFIG),y)
+linux-update linux26-update: $(LINUX26_DIR)/.config
+	cp -f $(LINUX26_DIR)/.config $(BR2_LINUX_KERNEL_CUSTOM_CONFIG_FILE)
+else
+linux-update linux26-update: ;
+endif
+
 # Support for rebuilding the kernel after the initramfs file list has
 # been generated in $(BINARIES_DIR)/rootfs.initramfs.
 $(LINUX26_DIR)/.stamp_initramfs_rebuilt: $(LINUX26_DIR)/.stamp_installed $(BINARIES_DIR)/rootfs.initramfs

@@ -10,6 +10,17 @@
 	string
 	option env="BR2_VERSION_FULL"
 
+config BR2_BACKUP_CONFIG
+	string "Backup configuration file"
+	default ""
+	help
+	  If you set a configuration file here and run 'make config-update',
+	  the buildroot configuration will be copied to that file.
+	  This can be useful if you want to put the buildroot configuration
+	  under version control.
+	  If you are working on a specific board, it may be a good idea to
+	  specify the board_defconfig file here.
+
 source "target/Config.in.arch"
 
 menu "Build options"

@@ -598,6 +598,7 @@
 %_defconfig: $(BUILD_DIR)/buildroot-config/conf $(TOPDIR)/configs/%_defconfig outputmakefile
 	@mkdir -p $(BUILD_DIR)/buildroot-config
 	@$(COMMON_CONFIG_ENV) $< --defconfig=$(TOPDIR)/configs/$@ $(CONFIG_CONFIG_IN)
+	@sed -i 's,BR2_BACKUP_CONFIG.*,BR2_BACKUP_CONFIG="$(TOPDIR)/configs/$@",' $(CONFIG_DIR)/.config
 
 savedefconfig: $(BUILD_DIR)/buildroot-config/conf outputmakefile
 	@mkdir -p $(BUILD_DIR)/buildroot-config

@@ -609,6 +610,14 @@
 
 endif # ifeq ($(BR2_HAVE_DOT_CONFIG),y)
 
+ifneq ($(BR2_BACKUP_CONFIG),"")
+config-update: $(CONFIG_DIR)/.config
+	cp -f $(CONFIG_DIR)/.config $(BR2_BACKUP_CONFIG)
+else
+config-update: ;
+endif
+
+
 #############################################################
 #
 # Cleanup and misc junk