kconfig: add helper to set config symbol from environment variable

Add conf_set_env_sym() that can set an already defined symbol
based on the value of an environment variable.

Unknown symbols are silently ignored.
A warning is printed if the value of the environment variable
is unexpected.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Cc: Roman Zippel <zippel@linux-m68k.org>

scripts/kconfig/confdata.c

@@ -145,6 +145,33 @@ static int conf_set_sym_val(struct symbol *sym, int def, int def_flags, char *p)
 	return 0;
 }
 
+/* Read an environment variable and assign the value to the symbol */
+int conf_set_env_sym(const char *env, const char *symname, int def)
+{
+	struct symbol *sym;
+	char *p;
+	int def_flags;
+
+	p = getenv(env);
+	if (p) {
+		char warning[200];
+		sprintf(warning, "Environment variable (%s = \"%s\")", env, p);
+		conf_filename = warning;
+		def_flags = SYMBOL_DEF << def;
+		if (def == S_DEF_USER) {
+			sym = sym_find(symname);
+			if (!sym)
+				return 1;
+		} else {
+			sym = sym_lookup(symname, 0);
+			if (sym->type == S_UNKNOWN)
+				sym->type = S_OTHER;
+		}
+		conf_set_sym_val(sym, def, def_flags, p);
+	}
+	return 0;
+}
+
 int conf_read_simple(const char *name, int def)
 {
 	FILE *in = NULL;

scripts/kconfig/lkc_proto.h

@@ -1,6 +1,7 @@
 
 /* confdata.c */
 P(conf_parse,void,(const char *name));
+P(conf_set_env_sym,int,(const char *envname, const char *symname, int def));
 P(conf_read,int,(const char *name));
 P(conf_read_simple,int,(const char *name, int));
 P(conf_write,int,(const char *name));