[settings] Make "netX" settings block function as a symbolic link

Add a facility for settings blocks to act as symbolic links to other
settings blocks, and reimplement the "netX" virtual settings block
using this facility.

The primary advantage of this approach is that unscoped settings such
as ${mac} and ${filename} will now reflect the settings obtained from
the most recently opened network device: in most cases, this will mean
the settings obtained from the most recent DHCP attempt.  This should
improve conformance to the principle of least astonishment.

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

1 files changed, 50 insertions, 23 deletions

diff --git a/src/core/settings.c b/src/core/settings.c
index 927ad845..80cd6a9f 100644
--- a/src/core/settings.c
+++ b/src/core/settings.c
@@ -271,6 +271,9 @@ struct settings * find_child_settings ( struct settings *parent,
 					const char *name ) {
 	struct settings *settings;
 
+	/* Find target parent settings block */
+	parent = settings_target ( parent );
+
 	/* Treat empty name as meaning "this block" */
 	if ( ! *name )
 		return parent;
@@ -278,7 +281,7 @@ struct settings * find_child_settings ( struct settings *parent,
 	/* Look for child with matching name */
 	list_for_each_entry ( settings, &parent->children, siblings ) {
 		if ( strcmp ( settings->name, name ) == 0 )
-			return settings;
+			return settings_target ( settings );
 	}
 
 	return NULL;
@@ -299,6 +302,9 @@ static struct settings * autovivify_child_settings ( struct settings *parent,
 	} *new_child;
 	struct settings *settings;
 
+	/* Find target parent settings block */
+	parent = settings_target ( parent );
+
 	/* Return existing settings, if existent */
 	if ( ( settings = find_child_settings ( parent, name ) ) != NULL )
 		return settings;
@@ -330,6 +336,10 @@ const char * settings_name ( struct settings *settings ) {
 	static char buf[16];
 	char tmp[ sizeof ( buf ) ];
 
+	/* Find target settings block */
+	settings = settings_target ( settings );
+
+	/* Construct name */
 	for ( buf[2] = buf[0] = 0 ; settings ; settings = settings->parent ) {
 		memcpy ( tmp, buf, sizeof ( tmp ) );
 		snprintf ( buf, sizeof ( buf ), ".%s%s", settings->name, tmp );
@@ -359,20 +369,11 @@ parse_settings_name ( const char *name,
 
 	/* Parse each name component in turn */
 	while ( remainder ) {
-		struct net_device *netdev;
-
 		subname = remainder;
 		remainder = strchr ( subname, '.' );
 		if ( remainder )
 			*(remainder++) = '\0';
-
-		/* Special case "netX" root settings block */
-		if ( ( subname == name_copy ) && ! strcmp ( subname, "netX" ) &&
-		     ( ( netdev = last_opened_netdev() ) != NULL ) )
-			settings = get_child ( settings, netdev->name );
-		else
-			settings = get_child ( settings, subname );
-
+		settings = get_child ( settings, subname );
 		if ( ! settings )
 			break;
 	}
@@ -460,10 +461,11 @@ int register_settings ( struct settings *settings, struct settings *parent,
 			const char *name ) {
 	struct settings *old_settings;
 
-	/* NULL parent => add to settings root */
+	/* Sanity check */
 	assert ( settings != NULL );
-	if ( parent == NULL )
-		parent = &settings_root;
+
+	/* Find target parent settings block */
+	parent = settings_target ( parent );
 
 	/* Apply settings block name */
 	settings->name = name;
@@ -524,6 +526,26 @@ void unregister_settings ( struct settings *settings ) {
  */
 
 /**
+ * Redirect to target settings block
+ *
+ * @v settings		Settings block, or NULL
+ * @ret settings	Underlying settings block
+ */
+struct settings * settings_target ( struct settings *settings ) {
+
+	/* NULL settings implies the global settings root */
+	if ( ! settings )
+		settings = &settings_root;
+
+	/* Redirect to underlying settings block, if applicable */
+	if ( settings->op->redirect )
+		return settings->op->redirect ( settings );
+
+	/* Otherwise, return this settings block */
+	return settings;
+}
+
+/**
  * Check applicability of setting
  *
  * @v settings		Settings block
@@ -532,6 +554,10 @@ void unregister_settings ( struct settings *settings ) {
  */
 int setting_applies ( struct settings *settings, struct setting *setting ) {
 
+	/* Find target settings block */
+	settings = settings_target ( settings );
+
+	/* Check applicability of setting */
 	return ( settings->op->applies ?
 		 settings->op->applies ( settings, setting ) : 1 );
 }
@@ -549,9 +575,8 @@ int store_setting ( struct settings *settings, struct setting *setting,
 		    const void *data, size_t len ) {
 	int rc;
 
-	/* NULL settings implies storing into the global settings root */
-	if ( ! settings )
-		settings = &settings_root;
+	/* Find target settings block */
+	settings = settings_target ( settings );
 
 	/* Fail if tag does not apply to this settings block */
 	if ( ! setting_applies ( settings, setting ) )
@@ -609,9 +634,8 @@ static int fetch_setting_and_origin ( struct settings *settings,
 	if ( origin )
 		*origin = NULL;
 
-	/* NULL settings implies starting at the global settings root */
-	if ( ! settings )
-		settings = &settings_root;
+	/* Find target settings block */
+	settings = settings_target ( settings );
 
 	/* Sanity check */
 	if ( ! settings->op->fetch )
@@ -971,6 +995,11 @@ int fetch_uuid_setting ( struct settings *settings, struct setting *setting,
  * @v settings		Settings block
  */
 void clear_settings ( struct settings *settings ) {
+
+	/* Find target settings block */
+	settings = settings_target ( settings );
+
+	/* Clear settings, if applicable */
 	if ( settings->op->clear )
 		settings->op->clear ( settings );
 }
@@ -1230,9 +1259,7 @@ int setting_name ( struct settings *settings, struct setting *setting,
 		   char *buf, size_t len ) {
 	const char *name;
 
-	if ( ! settings )
-		settings = &settings_root;
-
+	settings = settings_target ( settings );
 	name = settings_name ( settings );
 	return snprintf ( buf, len, "%s%s%s:%s", name, ( name[0] ? "/" : "" ),
 			  setting->name, setting->type->name );