env: make "env default" selective, check and apply

Change the syntax (user API) for "env default":
  -f: override write-once variables
  var... : accept individual variable(s)
  -a: all (resetting the whole env is NOT the default behavior)

Enable variable checking and make changes effective by
enabling do_apply argument to himport_r().

Signed-off-by: Gerlando Falauto <gerlando.falauto@keymile.com>

common/cmd_nvedit.c

@@ -656,15 +656,42 @@ int envmatch(uchar *s1, int i2)
 	return -1;
 }
 
-static int do_env_default(cmd_tbl_t *cmdtp, int flag,
+static int do_env_default(cmd_tbl_t *cmdtp, int __flag,
 			  int argc, char * const argv[])
 {
-	if (argc != 2 || strcmp(argv[1], "-f") != 0)
-		return CMD_RET_USAGE;
+	int all = 0, flag = 0;
 
+	debug("Initial value for argc=%d\n", argc);
+	while (--argc > 0 && **++argv == '-') {
+		char *arg = *argv;
+
+		while (*++arg) {
+			switch (*arg) {
+			case 'a':		/* default all */
+				all = 1;
+				break;
+			case 'f':		/* force */
+				flag |= H_FORCE;
+				break;
+			default:
+				return cmd_usage(cmdtp);
+			}
+		}
+	}
+	debug("Final value for argc=%d\n", argc);
+	if (all && (argc == 0)) {
+		/* Reset the whole environment */
 		set_default_env("## Resetting to default environment\n");
 		return 0;
 	}
+	if (!all && (argc > 0)) {
+		/* Reset individual variables */
+		set_default_vars(argc, argv);
+		return 0;
+	}
+
+	return cmd_usage(cmdtp);
+}
 
 static int do_env_delete(cmd_tbl_t *cmdtp, int flag,
 			 int argc, char * const argv[])
@@ -994,7 +1021,8 @@ U_BOOT_CMD(
 #if defined(CONFIG_CMD_ASKENV)
 	"ask name [message] [size] - ask for environment variable\nenv "
 #endif
-	"default -f - reset default environment\n"
+	"default [-f] -a - [forcibly] reset default environment\n"
+	"env default [-f] var [...] - [forcibly] reset variable(s) to their default values\n"
 #if defined(CONFIG_CMD_EDITENV)
 	"env edit name - edit environment variable\n"
 #endif

common/env_common.c

@@ -180,6 +180,11 @@ const uchar *env_get_addr(int index)
 
 void set_default_env(const char *s)
 {
+	/*
+	 * By default, do not apply changes as they will eventually
+	 * be applied by someone else
+	 */
+	int do_apply = 0;
 	if (sizeof(default_environment) > ENV_SIZE) {
 		puts("*** Error - default environment is too large\n\n");
 		return;
@@ -191,6 +196,14 @@ void set_default_env(const char *s)
 				"using default environment\n\n",
 				s + 1);
 		} else {
+			/*
+			 * This set_to_default was explicitly asked for
+			 * by the user, as opposed to being a recovery
+			 * mechanism.  Therefore we check every single
+			 * variable and apply changes to the system
+			 * right away (e.g. baudrate, console).
+			 */
+			do_apply = 1;
 			puts(s);
 		}
 	} else {
@@ -199,12 +212,25 @@ void set_default_env(const char *s)
 
 	if (himport_r(&env_htab, (char *)default_environment,
 			sizeof(default_environment), '\0', 0,
-			0, NULL, 0 /* do_apply */) == 0)
+			0, NULL, do_apply) == 0)
 		error("Environment import failed: errno = %d\n", errno);
 
 	gd->flags |= GD_FLG_ENV_READY;
 }
 
+
+/* [re]set individual variables to their value in the default environment */
+int set_default_vars(int nvars, char * const vars[])
+{
+	/*
+	 * Special use-case: import from default environment
+	 * (and use \0 as a separator)
+	 */
+	return himport_r(&env_htab, (const char *)default_environment,
+				sizeof(default_environment), '\0', H_NOCLEAR,
+				nvars, vars, 1 /* do_apply */);
+}
+
 /*
  * Check if CRC is valid and (if yes) import the environment.
  * Note that "buf" may or may not be aligned.

include/environment.h

@@ -181,6 +181,9 @@ void env_crc_update(void);
 /* [re]set to the default environment */
 void set_default_env(const char *s);
 
+/* [re]set individual variables to their value in the default environment */
+int set_default_vars(int nvars, char * const vars[]);
+
 /* Import from binary representation into hash table */
 int env_import(const char *buf, int check);