cmd: add a new command "config" to show .config contents

This feature is inspired by /proc/config.gz of Linux.  In Linux,
if CONFIG_IKCONFIG is enabled, the ".config" file contents are
embedded in the kernel image.  If CONFIG_IKCONFIG_PROC is also
enabled, the ".config" contents are exposed to /proc/config.gz.
Users can do "zcat /proc/config.gz" to check which config options
are enabled on the running kernel image.

The idea is almost the same here; if CONFIG_CMD_CONFIG is enabled,
the ".config" contents are compressed and saved in the U-Boot image,
then printed by the new command "config".

The usage is quite simple.  Enable CONFIG_CMD_CONFIG, then run
 > config
from the command line interface.  The ".config" contents will be
printed on the console.

This feature increases the U-Boot image size by about 4KB (this is
mostly due to the gzip-compressed .config file).  By default, it is
enabled only for Sandbox because we do not care about the memory
footprint on it.  Of course, this feature is architecture agnostic,
so you can enable it on any board if the image size increase is
acceptable for you.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

cmd/.gitignore

@@ -0,0 +1,3 @@
+config_data.gz
+config_data_gz.h
+config_data_size.h

cmd/Kconfig

@@ -126,6 +126,18 @@ config CMD_BDI
 	help
 	  Print board info
 
+config CMD_CONFIG
+	bool "config"
+	select BUILD_BIN2C
+	default SANDBOX
+	help
+	  Print ".config" contents.
+
+	  If this option is enabled, the ".config" file contents are embedded
+	  in the U-Boot image and can be printed on the console by the "config"
+	  command.  This provides information of which options are enabled on
+	  the running U-Boot.
+
 config CMD_CONSOLE
 	bool "coninfo"
 	default y

cmd/Makefile

@@ -31,6 +31,7 @@ obj-$(CONFIG_CMD_BOOTI) += booti.o
 obj-$(CONFIG_CMD_CACHE) += cache.o
 obj-$(CONFIG_CMD_CBFS) += cbfs.o
 obj-$(CONFIG_CMD_CLK) += clk.o
+obj-$(CONFIG_CMD_CONFIG) += config.o
 obj-$(CONFIG_CMD_CONSOLE) += console.o
 obj-$(CONFIG_CMD_CPLBINFO) += cplbinfo.o
 obj-$(CONFIG_CMD_CPU) += cpu.o
@@ -165,3 +166,24 @@ obj-$(CONFIG_CMD_BLOB) += blob.o
 obj-y += nvedit.o
 
 obj-$(CONFIG_ARCH_MVEBU) += mvebu/
+
+filechk_data_gz = (echo "static const char data_gz[] ="; cat $< | scripts/bin2c; echo ";")
+
+filechk_data_size = \
+	(echo "static const size_t data_size = "; \
+	cat $< | wc -c; echo ";")
+
+# "config" command
+$(obj)/config.o: $(obj)/config_data_gz.h $(obj)/config_data_size.h
+
+targets += config_data.gz
+$(obj)/config_data.gz: $(KCONFIG_CONFIG) FORCE
+	$(call if_changed,gzip)
+
+targets += config_data_gz.h
+$(obj)/config_data_gz.h: $(obj)/config_data.gz FORCE
+	$(call filechk,data_gz)
+
+targets += config_data_size.h
+$(obj)/config_data_size.h: $(KCONFIG_CONFIG) FORCE
+	$(call filechk,data_size)

cmd/config.c

@@ -0,0 +1,44 @@
+/*
+ * Copyright (C) 2017 Masahiro Yamada <yamada.masahiro@socionext.com>
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#include <common.h>
+#include <command.h>
+#include <malloc.h>
+
+#include "config_data_gz.h"
+#include "config_data_size.h"
+
+static int do_config(cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[])
+{
+	char *dst;
+	unsigned long len = data_size;
+	int ret = CMD_RET_SUCCESS;
+
+	dst = malloc(data_size + 1);
+	if (!dst)
+		return CMD_RET_FAILURE;
+
+	ret = gunzip(dst, data_size, (unsigned char *)data_gz, &len);
+	if (ret) {
+		printf("failed to uncompress .config data\n");
+		ret = CMD_RET_FAILURE;
+		goto free;
+	}
+
+	dst[data_size] = 0;
+	puts(dst);
+
+free:
+	free(dst);
+
+	return ret;
+}
+
+U_BOOT_CMD(
+	config, 1, 1, do_config,
+	"print .config",
+	""
+);