[settings] Add the notion of a "tag magic" to numbered settings

Settings can be constructed using a dotted-decimal notation, to allow
for access to unnamed settings.  The default interpretation is as a
DHCP option number (with encapsulated options represented as
"<encapsulating option>.<encapsulated option>".

In several contexts (e.g. SMBIOS, Phantom CLP), it is useful to
interpret the dotted-decimal notation as referring to non-DHCP
options.  In this case, it becomes necessary for these contexts to
ignore standard DHCP options, otherwise we end up trying to, for
example, retrieve the boot filename from SMBIOS.

Allow settings blocks to specify a "tag magic".  When dotted-decimal
notation is used to construct a setting, the tag magic value of the
originating settings block will be ORed in to the tag number.
Store/fetch methods can then check for the magic number before
interpreting arbitrarily-numbered settings.

src/arch/i386/firmware/pcbios/smbios_settings.c

 #include <gpxe/uuid.h>
 #include <smbios.h>
 
+/** SMBIOS settings tag magic number */
+#define SMBIOS_TAG_MAGIC 0x5B /* "SmBios" */
+
+/**
+ * Construct SMBIOS empty tag
+ *
+ * @ret tag		SMBIOS setting tag
+ */
+#define SMBIOS_EMPTY_TAG ( SMBIOS_TAG_MAGIC << 24 )
+
 /**
  * Construct SMBIOS raw-data tag
  *
  * @ret tag		SMBIOS setting tag
  */
 #define SMBIOS_RAW_TAG( _type, _structure, _field )		\
-	( ( (_type) << 16 ) |					\
+	( ( SMBIOS_TAG_MAGIC << 24 ) |				\
+	  ( (_type) << 16 ) |					\
 	  ( offsetof ( _structure, _field ) << 8 ) |		\
 	  ( sizeof ( ( ( _structure * ) 0 )->_field ) ) )
 
  * @ret tag		SMBIOS setting tag
  */
 #define SMBIOS_STRING_TAG( _type, _structure, _field )		\
-	( ( (_type) << 16 ) |					\
+	( ( SMBIOS_TAG_MAGIC << 24 ) |				\
+	  ( (_type) << 16 ) |					\
 	  ( offsetof ( _structure, _field ) << 8 ) )
 
 /**
 			  struct setting *setting,
 			  void *data, size_t len ) {
 	struct smbios_structure structure;
+	unsigned int tag_magic;
 	unsigned int tag_type;
 	unsigned int tag_offset;
 	unsigned int tag_len;
 	int rc;
 
 	/* Split tag into type, offset and length */
-	tag_type = ( setting->tag >> 16 );
+	tag_magic = ( setting->tag >> 24 );
+	tag_type = ( ( setting->tag >> 16 ) & 0xff );
 	tag_offset = ( ( setting->tag >> 8 ) & 0xff );
 	tag_len = ( setting->tag & 0xff );
-	if ( ! tag_type )
+	if ( tag_magic != SMBIOS_TAG_MAGIC )
 		return -ENOENT;
 
 	/* Find SMBIOS structure */
 static struct settings smbios_settings = {
 	.refcnt = NULL,
 	.name = "smbios",
+	.tag_magic = SMBIOS_EMPTY_TAG,
 	.siblings = LIST_HEAD_INIT ( smbios_settings.siblings ),
 	.children = LIST_HEAD_INIT ( smbios_settings.children ),
 	.op = &smbios_settings_operations,

src/core/nvo.c

 	nvo->nvs = nvs;
 	nvo->fragments = fragments;
 	settings_init ( &nvo->settings, &nvo_settings_operations, refcnt,
-			"nvo" );
+			"nvo", 0 );
 }
 
 /**

src/core/settings.c

 			}
 			tmp++;
 		}
+		setting->tag |= (*settings)->tag_magic;
 	}
 
 	/* Identify setting type, if specified */

src/drivers/net/phantom/phantom.c

  *
  */
 
+/** Phantom CLP settings tag magic */
+#define PHN_CLP_TAG_MAGIC 0xc19c1900UL
+
+/** Phantom CLP settings tag magic mask */
+#define PHN_CLP_TAG_MAGIC_MASK 0xffffff00UL
+
 /** Phantom CLP data
  *
  */
 	/** gPXE setting */
 	struct setting *setting;
 	/** Setting number */
-	unsigned int number;
+	unsigned int clp_setting;
 };
 
 /** Phantom CLP settings */
  * Find Phantom CLP setting
  *
  * @v setting		gPXE setting
- * @v clp_setting	Equivalent Phantom CLP setting, or NULL
+ * @v clp_setting	Setting number, or 0 if not found
  */
-static struct phantom_clp_setting *
-phantom_find_clp_setting ( struct phantom_nic *phantom,
-			   struct setting *setting ) {
+static unsigned int
+phantom_clp_setting ( struct phantom_nic *phantom, struct setting *setting ) {
 	struct phantom_clp_setting *clp_setting;
 	unsigned int i;
 
+	/* Search the list of explicitly-defined settings */
 	for ( i = 0 ; i < ( sizeof ( clp_settings ) /
 			    sizeof ( clp_settings[0] ) ) ; i++ ) {
 		clp_setting = &clp_settings[i];
 		if ( setting_cmp ( setting, clp_setting->setting ) == 0 )
-			return clp_setting;
+			return clp_setting->clp_setting;
 	}
 
+	/* Allow for use of numbered settings */
+	if ( ( setting->tag & PHN_CLP_TAG_MAGIC_MASK ) == PHN_CLP_TAG_MAGIC )
+		return ( setting->tag & ~PHN_CLP_TAG_MAGIC_MASK );
+
 	DBGC2 ( phantom, "Phantom %p has no \"%s\" setting\n",
 		phantom, setting->name );
 
-	return NULL;
+	return 0;
 }
 
 /**
 	struct phantom_nic_port *phantom_port =
 		container_of ( settings, struct phantom_nic_port, settings );
 	struct phantom_nic *phantom = phantom_port->phantom;
-	struct phantom_clp_setting *clp_setting;
+	unsigned int clp_setting;
 	int rc;
 
 	/* Find Phantom setting equivalent to gPXE setting */
-	clp_setting = phantom_find_clp_setting ( phantom, setting );
+	clp_setting = phantom_clp_setting ( phantom, setting );
 	if ( ! clp_setting )
 		return -ENOTSUP;
 
 	/* Store setting */
 	if ( ( rc = phantom_clp_store ( phantom, phantom_port->port,
-					clp_setting->number,
-					data, len ) ) != 0 ) {
+					clp_setting, data, len ) ) != 0 ) {
 		DBGC ( phantom, "Phantom %p could not store setting \"%s\": "
 		       "%s\n", phantom, setting->name, strerror ( rc ) );
 		return rc;
 	struct phantom_nic_port *phantom_port =
 		container_of ( settings, struct phantom_nic_port, settings );
 	struct phantom_nic *phantom = phantom_port->phantom;
-	struct phantom_clp_setting *clp_setting;
+	unsigned int clp_setting;
 	int read_len;
 	int rc;
 
 	/* Find Phantom setting equivalent to gPXE setting */
-	clp_setting = phantom_find_clp_setting ( phantom, setting );
+	clp_setting = phantom_clp_setting ( phantom, setting );
 	if ( ! clp_setting )
 		return -ENOTSUP;
 
 	/* Fetch setting */
 	if ( ( read_len = phantom_clp_fetch ( phantom, phantom_port->port,
-					      clp_setting->number,
-					      data, len ) ) < 0 ) {
+					      clp_setting, data, len ) ) < 0 ){
 		rc = read_len;
 		DBGC ( phantom, "Phantom %p could not fetch setting \"%s\": "
 		       "%s\n", phantom, setting->name, strerror ( rc ) );
 		phantom_port->port = i;
 		settings_init ( &phantom_port->settings,
 				&phantom_settings_operations,
-				&netdev->refcnt, "clp" );
+				&netdev->refcnt, "clp", PHN_CLP_TAG_MAGIC );
 	}
 
 	/* BUG5945 - need to hack PCI config space on P3 B1 silicon.

src/include/gpxe/settings.h

 	struct refcnt *refcnt;
 	/** Name */
 	const char *name;
+	/** Tag magic
+	 *
+	 * This value will be ORed in to any numerical tags
+	 * constructed by parse_setting_name(), and can be used to
+	 * avoid e.g. attempting to retrieve the subnet mask from
+	 * SMBIOS, or the system UUID from DHCP.
+	 */
+	unsigned int tag_magic;
 	/** Parent settings block */
 	struct settings *parent;
 	/** Sibling settings blocks */
  * @v op		Settings block operations
  * @v refcnt		Containing object reference counter, or NULL
  * @v name		Settings block name
+ * @v tag_magic		Tag magic
  */
 static inline void settings_init ( struct settings *settings,
 				   struct settings_operations *op,
 				   struct refcnt *refcnt,
-				   const char *name ) {
+				   const char *name,
+				   unsigned int tag_magic ) {
 	INIT_LIST_HEAD ( &settings->siblings );
 	INIT_LIST_HEAD ( &settings->children );
 	settings->op = op;
 	settings->refcnt = refcnt;
 	settings->name = name;
+	settings->tag_magic = tag_magic;
 }
 
 /**
 					  struct refcnt *refcnt,
 					  const char *name ) {
 	settings_init ( &simple->settings, &simple_settings_operations,
-			refcnt, name );
+			refcnt, name, 0 );
 }
 
 /**

src/net/netdevice.c

 		INIT_LIST_HEAD ( &netdev->rx_queue );
 		settings_init ( netdev_settings ( netdev ),
 				&netdev_settings_operations, &netdev->refcnt,
-				netdev->name );
+				netdev->name, 0 );
 		netdev->priv = ( ( ( void * ) netdev ) + sizeof ( *netdev ) );
 	}
 	return netdev;

src/net/udp/dhcp.c

 		dhcppkt_init ( &dhcpset->dhcppkt, data, len );
 		settings_init ( &dhcpset->settings,
 				&dhcpset_settings_operations, &dhcpset->refcnt,
-				DHCP_SETTINGS_NAME );
+				DHCP_SETTINGS_NAME, 0 );
 	}
 	return dhcpset;
 }