env: add a version number to check API

Changes in the environment library are difficult to tracked by programs
using the library. Add simply an API version number that must be
increased each time when the API is changed.

This can be detected and a program can work with different versions of
the library.

Signed-off-by: Stefano Babic <sbabic@denx.de>

tools/env/fw_env.h

@@ -8,6 +8,13 @@
 #include <stdint.h>
 #include <uboot_aes.h>
 
+/*
+ * Programs using the library must check which API is available,
+ * that varies depending on the U-Boot version.
+ * This can be changed in future
+ */
+#define FW_ENV_API_VERSION	1
+
 struct env_opts {
 #ifdef CONFIG_FILE
 	char *config_file;
@@ -140,4 +147,12 @@ int fw_env_write(char *name, char *value);
  */
 int fw_env_close(struct env_opts *opts);
 
+/**
+ * fw_env_version - return the current version of the library
+ *
+ * Return:
+ *  version string of the library
+ */
+char *fw_env_version(void);
+
 unsigned long crc32(unsigned long, const unsigned char *, unsigned);