[settings] Allow for writable built-in settings

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/core/settings.c

@@ -2758,6 +2758,30 @@ struct builtin_setting cwduri_builtin_setting __builtin_setting = {
 	.fetch = cwduri_fetch,
 };
 
+/**
+ * Store built-in setting
+ *
+ * @v settings		Settings block
+ * @v setting		Setting to store
+ * @v data		Setting data, or NULL to clear setting
+ * @v len		Length of setting data
+ * @ret rc		Return status code
+ */
+static int builtin_store ( struct settings *settings __unused,
+			   const struct setting *setting,
+			   const void *data, size_t len ) {
+	struct builtin_setting *builtin;
+
+	for_each_table_entry ( builtin, BUILTIN_SETTINGS ) {
+		if ( setting_cmp ( setting, builtin->setting ) == 0 ) {
+			if ( ! builtin->store )
+				return -ENOTSUP;
+			return builtin->store ( data, len );
+		}
+	}
+	return -ENOENT;
+}
+
 /**
  * Fetch built-in setting
  *
@@ -2795,6 +2819,7 @@ static int builtin_applies ( struct settings *settings __unused,
 /** Built-in settings operations */
 static struct settings_operations builtin_settings_operations = {
 	.applies = builtin_applies,
+	.store = builtin_store,
 	.fetch = builtin_fetch,
 };
 

src/include/ipxe/settings.h

@@ -268,6 +268,14 @@ struct settings_applicator {
 struct builtin_setting {
 	/** Setting */
 	const struct setting *setting;
+	/**
+	 * Store setting value
+	 *
+	 * @v data		Setting data, or NULL to clear setting
+	 * @v len		Length of setting data
+	 * @ret rc		Return status code
+	 */
+	int ( * store ) ( const void *data, size_t len );
 	/** Fetch setting value
 	 *
 	 * @v data		Buffer to fill with setting data