[dhcp] Send user class in DHCP requests

src/include/gpxe/dhcp.h

  */
 #define DHCP_BOOTFILE_NAME 67
 
+/** User class identifier */
+#define DHCP_USER_CLASS_ID 77
+
 /** Client system architecture */
 #define DHCP_CLIENT_ARCHITECTURE 93
 

src/include/gpxe/settings.h

 extern struct setting username_setting __setting;
 extern struct setting password_setting __setting;
 extern struct setting priority_setting __setting;
-extern struct setting bios_drive_setting __setting;
 extern struct setting uuid_setting __setting;
 extern struct setting next_server_setting __setting;
 extern struct setting mac_setting __setting;
+extern struct setting user_class_setting __setting;
 
 /**
  * Initialise a settings block

src/net/udp/dhcp.c

 	.type = &setting_type_ipv4,
 };
 
+/** DHCP user class setting */
+struct setting user_class_setting __setting = {
+	.name = "user-class",
+	.description = "User class identifier",
+	.tag = DHCP_USER_CLASS_ID,
+	.type = &setting_type_string,
+};
+
 /**
  * Name a DHCP packet type
  *
 	struct dhcp_client_uuid client_uuid;
 	size_t dhcp_features_len;
 	size_t ll_addr_len;
+	ssize_t len;
 	int rc;
 
 	/* Create DHCP packet */
 
 	/* Add client UUID, if we have one.  Required for PXE. */
 	client_uuid.type = DHCP_CLIENT_UUID_TYPE;
-	if ( ( rc = fetch_uuid_setting ( NULL, &uuid_setting,
-					 &client_uuid.uuid ) ) >= 0 ) {
+	if ( ( len = fetch_uuid_setting ( NULL, &uuid_setting,
+					  &client_uuid.uuid ) ) >= 0 ) {
 		if ( ( rc = dhcppkt_store ( dhcppkt, DHCP_CLIENT_UUID,
 					    &client_uuid,
 					    sizeof ( client_uuid ) ) ) != 0 ) {
 		}
 	}
 
+	/* Add user class, if we have one. */
+	if ( ( len = fetch_setting_len ( NULL, &user_class_setting ) ) >= 0 ) {
+		char user_class[len];
+		fetch_setting ( NULL, &user_class_setting, user_class,
+				sizeof ( user_class ) );
+		if ( ( rc = dhcppkt_store ( dhcppkt, DHCP_USER_CLASS_ID,
+					    &user_class,
+					    sizeof ( user_class ) ) ) != 0 ) {
+			DBG ( "DHCP could not set user class: %s\n",
+			      strerror ( rc ) );
+			return rc;
+		}
+	}
+
 	return 0;
 }