[settings] Allow for multiple definitions of each predefined setting

Allow for multiple setting definitions with the same name but
different scopes and tags.  For example, allow for a "filename"
setting with default scope and tag value 67 (for DHCPv4) and a
corresponding "filename" setting with IPv6 scope and tag value 59 (for
DHCPv6).

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

src/core/settings.c

 		 settings->op->applies ( settings, setting ) : 1 );
 }
 
+/**
+ * Find setting applicable to settings block, if any
+ *
+ * @v settings		Settings block
+ * @v setting		Setting
+ * @ret setting		Applicable setting, if any
+ */
+static const struct setting *
+applicable_setting ( struct settings *settings, const struct setting *setting ){
+	const struct setting *applicable;
+
+	/* If setting is already applicable, use it */
+	if ( setting_applies ( settings, setting ) )
+		return setting;
+
+	/* Otherwise, look for a matching predefined setting which does apply */
+	for_each_table_entry ( applicable, SETTINGS ) {
+		if ( ( setting_cmp ( setting, applicable ) == 0 ) &&
+		     ( setting_applies ( settings, applicable ) ) )
+			return applicable;
+	}
+
+	return NULL;
+}
+
 /**
  * Store value of setting
  *
 	/* Find target settings block */
 	settings = settings_target ( settings );
 
-	/* Fail if tag does not apply to this settings block */
+	/* Fail if setting does not apply to this settings block */
 	if ( ! setting_applies ( settings, setting ) )
 		return -ENOTTY;
 
 int fetch_setting ( struct settings *settings, const struct setting *setting,
 		    struct settings **origin, struct setting *fetched,
 		    void *data, size_t len ) {
+	const struct setting *applicable;
 	struct settings *child;
 	struct setting tmp;
 	int ret;
 	if ( ! settings->op->fetch )
 		return -ENOTSUP;
 
-	/* Try this block first, if applicable */
-	if ( setting_applies ( settings, setting ) ) {
+	/* Try this block first, if an applicable setting exists */
+	if ( ( applicable = applicable_setting ( settings, setting ) ) ) {
 
 		/* Create modifiable copy of setting */
-		memcpy ( &tmp, setting, sizeof ( tmp ) );
+		memcpy ( &tmp, applicable, sizeof ( tmp ) );
 		if ( ( ret = settings->op->fetch ( settings, &tmp,
 						   data, len ) ) >= 0 ) {
 

src/hci/tui/settings_ui.c

 					 unsigned int index ) {
 	struct settings *settings;
 	struct setting *setting;
+	struct setting *previous = NULL;
 	unsigned int count = 0;
 
 	/* Initialise structure */
 
 	/* Include any applicable settings */
 	for_each_table_entry ( setting, SETTINGS ) {
+
+		/* Skip inapplicable settings */
 		if ( ! setting_applies ( widget->settings, setting ) )
 			continue;
-		if ( count++ == index ) {
 
-			/* Read current setting value and origin */
+		/* Skip duplicate settings */
+		if ( previous && ( setting_cmp ( setting, previous ) == 0 ) )
+			continue;
+		previous = setting;
+
+		/* Read current setting value and origin */
+		if ( count++ == index ) {
 			fetchf_setting ( widget->settings, setting,
 					 &widget->row.origin,
 					 &widget->row.setting,

src/interface/efi/efi_snp_hii.c

 				    struct efi_ifr_builder *ifr,
 				    unsigned int varstore_id ) {
 	struct setting *setting;
+	struct setting *previous = NULL;
 	unsigned int name_id;
 	unsigned int prompt_id;
 	unsigned int help_id;
 	for_each_table_entry ( setting, SETTINGS ) {
 		if ( ! efi_snp_hii_setting_applies ( snpdev, setting ) )
 			continue;
+		if ( previous && ( setting_cmp ( setting, previous ) == 0 ) )
+			continue;
+		previous = setting;
 		name_id = efi_ifr_string ( ifr, "%s", setting->name );
 		prompt_id = efi_ifr_string ( ifr, "%s", setting->description );
 		help_id = efi_ifr_string ( ifr, "http://ipxe.org/cfg/%s",