Add FEATURE() macro, plus code to display features at startup time,

and generate DHCP options to indicate features to DHCP server (and to
PXE NBPs).

src/hci/shell_banner.c

 #include <stdio.h>
 #include <console.h>
 #include <latch.h>
+#include <gpxe/features.h>
 #include <gpxe/shell_banner.h>
 
 /** @file
 #define BOLD	"\033[1m"
 #define CYAN	"\033[36m"
 
+static char * features[0] __table_start ( char *, features );
+static char * features_end[0] __table_end ( char *, features );
+
 /**
  * Print shell banner and prompt for shell entry
  *
  */
 int shell_banner ( void ) {
 	unsigned long timeout = ( currticks() + BANNER_TIMEOUT );
+	char **feature;
 	int key;
 	int enter_shell = 0;
 
 	printf ( NORMAL "\n\n\n" BOLD "gPXE " VERSION
 		 NORMAL " -- Open Source Boot Firmware -- "
 		 CYAN "http://etherboot.org" NORMAL "\n"
-		 "Press Ctrl-B for the gPXE command line..." );
+		 "Features:" );
+	for ( feature = features ; feature < features_end ; feature++ ) {
+		printf ( " %s", *feature );
+	}
+	printf ( "\nPress Ctrl-B for the gPXE command line..." );
 
 	/* Wait for key */
 	while ( currticks() < timeout ) {

src/include/gpxe/dhcp.h

  */
 #define DHCP_EB_SIADDR DHCP_ENCAP_OPT ( DHCP_EB_ENCAP, 3 )
 
+/*
+ * Tags in the range 0x10-0x7f are reserved for feature markers
+ *
+ */
+
 /** Network device descriptor
  *
  * Byte 0 is the bus type ID; remaining bytes depend on the bus type.

src/include/gpxe/features.h

+#ifndef _GPXE_FEATURES_H
+#define _GPXE_FEATURES_H
+
+#include <stdint.h>
+#include <gpxe/tables.h>
+#include <gpxe/dhcp.h>
+
+/** @file
+ *
+ * Feature list
+ *
+ */
+
+/**
+ * @defgroup dhcpfeatures DHCP feature option tags
+ *
+ * DHCP feature option tags are Etherboot encapsulated options in the
+ * range 0x10-0x7f.
+ *
+ * @{
+ */
+
+/** PXE API extensions */
+#define DHCP_EB_FEATURE_PXE_EXT 0x10
+
+/** iSCSI */
+#define DHCP_EB_FEATURE_ISCSI 0x11
+
+/** AoE */
+#define DHCP_EB_FEATURE_AOE 0x12
+
+/** @} */
+
+/** Declare a feature code for DHCP */
+#define __dhcp_feature __table ( uint8_t, dhcp_features, 01 )
+
+/** Construct a DHCP feature table entry */
+#define DHCP_FEATURE( feature_opt ) \
+	_DHCP_FEATURE ( OBJECT, feature_opt )
+#define _DHCP_FEATURE( _name, feature_opt ) \
+	__DHCP_FEATURE ( _name, feature_opt )
+#define __DHCP_FEATURE( _name, feature_opt )			\
+	uint8_t __dhcp_feature_ ## _name [] __dhcp_feature = {	\
+		feature_opt, DHCP_BYTE ( 1 )			\
+	};
+
+/** Declare a named feature */
+#define __feature_name __table ( char *, features, 01 )
+
+/** Construct a named feature */
+#define FEATURE_NAME( text ) \
+	_FEATURE_NAME ( OBJECT, text )
+#define _FEATURE_NAME( _name, text ) \
+	__FEATURE_NAME ( _name, text )
+#define __FEATURE_NAME( _name, text )				\
+	char * __feature_ ## _name __feature_name = text;
+
+/** Declare a feature */
+#define FEATURE( text, feature_opt )				\
+	FEATURE_NAME ( text );					\
+	DHCP_FEATURE ( feature_opt );
+
+#endif /* _GPXE_FEATURES_H */

src/net/aoe.c

 #include <gpxe/ata.h>
 #include <gpxe/netdevice.h>
 #include <gpxe/process.h>
+#include <gpxe/features.h>
 #include <gpxe/aoe.h>
 
 /** @file
  *
  */
 
+FEATURE ( "AoE", DHCP_EB_FEATURE_AOE );
+
 struct net_protocol aoe_protocol;
 
 /** List of all AoE sessions */

src/net/tcp/iscsi.c

 #include <gpxe/uaccess.h>
 #include <gpxe/tcpip.h>
 #include <gpxe/dhcp.h>
+#include <gpxe/features.h>
 #include <gpxe/iscsi.h>
 
 /** @file
  *
  */
 
+FEATURE ( "iSCSI", DHCP_EB_FEATURE_ISCSI );
+
 /** iSCSI initiator name (explicitly specified) */
 static char *iscsi_explicit_initiator_iqn;
 

src/net/udp/dhcp.c

 	DHCP_END
 };
 
+/** DHCP feature codes */
+static uint8_t dhcp_features[0] __table_start ( uint8_t, dhcp_features );
+static uint8_t dhcp_features_end[0] __table_end ( uint8_t, dhcp_features );
+
 /**
  * Name a DHCP packet type
  *
 			  struct dhcp_packet *dhcppkt ) {
 	struct device_description *desc = &netdev->dev->desc;
 	struct dhcp_netdev_desc dhcp_desc;
+	size_t dhcp_features_len;
 	int rc;
 
 	/* Create DHCP packet */
 		}
 	}
 
+	/* Add options to identify the feature list */
+	dhcp_features_len = ( dhcp_features_end - dhcp_features );
+	if ( ( rc = set_dhcp_packet_option ( dhcppkt, DHCP_EB_ENCAP,
+					     dhcp_features,
+					     dhcp_features_len ) ) != 0 ) {
+		DBG ( "DHCP could not set features list option: %s\n",
+		      strerror ( rc ) );
+		return rc;
+	}
+
 	/* Add options to identify the network device */
 	dhcp_desc.type = desc->bus_type;
 	dhcp_desc.vendor = htons ( desc->vendor );