env: Make environment variable support optional

Environment variables are only useful in interactive environments.
Make it optional on our way to support a noninteractive barebox.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

commands/Kconfig

@@ -29,11 +29,13 @@ config CMD_LOADENV
 	prompt "loadenv"
 
 config CMD_EXPORT
+	depends on ENVIRONMENT_VARIABLES
 	tristate
 	prompt "export"
 
 config CMD_PRINTENV
 	tristate
+	depends on ENVIRONMENT_VARIABLES
 	prompt "printenv"
 
 config CMD_READLINE

common/Kconfig

@@ -62,6 +62,9 @@ config LOCALVERSION_AUTO
 config BOARDINFO
 	string
 
+config ENVIRONMENT_VARIABLES
+	bool "environment variables support"
+
 menu "memory layout                 "
 
 config HAVE_MMU
@@ -219,12 +222,14 @@ choice
 
 	config SHELL_HUSH
 		bool "hush parser"
+		select ENVIRONMENT_VARIABLES
 		help
 		  Enable hush support. This is the most advanced shell available
 		  for barebox.
 
 	config SHELL_SIMPLE
 		bool "Simple parser"
+		select ENVIRONMENT_VARIABLES
 		help
 		  simple shell. No if/then, no return values from commands, no loops
 endchoice

common/Makefile

@@ -15,7 +15,7 @@ obj-y += command.o
 obj-$(CONFIG_CONSOLE_FULL) += console.o
 obj-$(CONFIG_CONSOLE_SIMPLE) += console_simple.o
 obj-$(CONFIG_DIGEST) += digest.o
-obj-y += env.o
+obj-$(CONFIG_ENVIRONMENT_VARIABLES) += env.o
 obj-$(CONFIG_CMD_BOOTM) += image.o
 obj-y += startup.o
 obj-y += misc.o

include/environment.h

@@ -44,8 +44,20 @@ struct env_context *get_current_context(void);
 char *var_val(struct variable_d *);
 char *var_name(struct variable_d *);
 
+#ifdef CONFIG_ENVIRONMENT_VARIABLES
 const char *getenv(const char *);
 int setenv(const char *, const char *);
+#else
+static inline char *getenv(const char *var)
+{
+	return NULL;
+}
+
+static inline int setenv(const char *var, const char *val)
+{
+	return 0;
+}
+#endif
 
 int env_pop_context(void);
 int env_push_context(void);