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/include/gpxe/dhcp.h

@@ -168,6 +168,11 @@ struct job_interface;
  */
 #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

@@ -0,0 +1,63 @@
+#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 */