samples: add rule to dump current .config into a defconfig

... and one to restore it, of course.

Reported-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>

ct-ng.comp

@@ -15,13 +15,14 @@ _ct_ng () {
     stop_steps=$(echo "${steps}" |sed -r -e 's/(^| )/+\1/;')
 
     actions='help menuconfig oldconfig saveconfig extractconfig
+             defconfig olddefconfig
              build build. build-all build-all.
              wiki-samples list-samples list-samples-short list-steps
              show-tuple show-all show-config
              clean distclean updatetools
              tarball version'
 
-    vars="RESTART= STOP= PREFIX= V="
+    vars="RESTART= STOP= PREFIX= V= DEFCONFIG="
 
     ct_ng_opts="${samples} ${show_samples} ${build_samples}
                 ${steps} ${start_steps} ${stop_steps}

docs/ct-ng.1.in

@@ -60,6 +60,47 @@ Samples can be later recalled by calling
 with the target tuple they represent.
 ."
 .TP
+.B defconfig
+Save the current configuration to a mini-defconfig file, that contains only
+the strictly required symbols to reproduce the configuraiton. defconfig files
+are much smaller than a complete .config, so it is easy to send by mail. As
+only non-default symbols are present in a defconfig, it easy to spot the
+meaningfull values. Also, it is easy to use defconfig files with newer
+versions of
+.BR crosstool-NG .
+By default the mini-defconfig is saved to a file named
+.IR defconfig ,
+unless the variable
+.B $DEFCONFIG
+is set, in which case the mini-defconfig will be saved to the file referenced
+by
+.BR $DEFCONFIG .
+
+Note: only the
+.I .config
+file for
+.B crosstool-NG
+is saved. Config files for the components are
+.B not
+saved. Use
+.B saveconfig
+for that
+."
+.TP
+.B olddefconfig
+Configure
+.B crosstool-NG
+using a mini-defconfig file (previously saved with
+.B defconfig
+or manually edited). The default mini-defconfig is rad from the file
+.IR defconfig ,
+unless the vraiable
+.B $DEFCONFIG
+is set, inwhich case the mini-defconfig will be read from the file referenced
+by
+.B $DEFCONFIG
+."
+.TP
 .B build
 Builds the configured toolchain.
 ."

kconfig/kconfig.mk

@@ -5,7 +5,7 @@
 #-----------------------------------------------------------
 # The configurators rules
 
-configurators = menuconfig nconfig oldconfig
+configurators = menuconfig nconfig oldconfig defconfig olddefconfig
 PHONY += $(configurators)
 
 $(configurators): config_files
@@ -27,6 +27,14 @@ oldconfig: .config
 	@$(ECHO) "  CONF  $(KCONFIG_TOP)"
 	$(SILENT)$(CONF) --silent$@ $(KCONFIG_TOP)
 
+defconfig: .config
+	@$(ECHO) '  GEN   $@'
+	$(SILENT)$(CONF) --savedefconfig=$${CONFIG-defconfig} $(KCONFIG_TOP)
+
+olddefconfig:
+	@$(ECHO) '  CONF  $@'
+	$(SILENT)$(CONF) --defconfig=$${CONFIG-defconfig} $(KCONFIG_TOP)
+
 # Always be silent, the stdout an be >.config
 extractconfig:
 	@$(awk) 'BEGIN { dump=0; }                                                  \
@@ -50,3 +58,6 @@ help-config::
 	@echo  '  oldconfig          - Update current config using a provided .config as base'
 	@echo  '  extractconfig      - Extract to stdout the configuration items from a'
 	@echo  '                       build.log file piped to stdin'
+	@echo  '  defconfig          - Save current config as a mini-defconfig to $${CONFIG}'
+	@echo  '  olddefconfig       - Update config from a mini-defconfig $${CONFIG}'
+	@echo  '                       (default: $${CONFIG}=./defconfig)'