[settings] Add Bus ID setting

Users can find the bus type and PCI IDs for a network interface with:

netX/busid

Signed-off-by: Stefan Hajnoczi <stefanha@gmail.com>

src/include/gpxe/settings.h

 extern struct setting uuid_setting __setting;
 extern struct setting next_server_setting __setting;
 extern struct setting mac_setting __setting;
+extern struct setting busid_setting __setting;
 extern struct setting user_class_setting __setting;
 
 /**

src/net/netdev_settings.c

 
 #include <string.h>
 #include <errno.h>
+#include <byteswap.h>
 #include <gpxe/dhcp.h>
 #include <gpxe/settings.h>
+#include <gpxe/device.h>
 #include <gpxe/netdevice.h>
 
 /** @file
 	.description = "MAC address",
 	.type = &setting_type_hex,
 };
+struct setting busid_setting __setting = {
+	.name = "busid",
+	.description = "Bus ID",
+	.type = &setting_type_hex,
+};
 
 /**
  * Store value of network device setting
 			  void *data, size_t len ) {
 	struct net_device *netdev = container_of ( settings, struct net_device,
 						   settings.settings );
+	struct device_description *desc = &netdev->dev->desc;
+	struct dhcp_netdev_desc dhcp_desc;
 
 	if ( setting_cmp ( setting, &mac_setting ) == 0 ) {
 		if ( len > netdev->ll_protocol->ll_addr_len )
 		memcpy ( data, netdev->ll_addr, len );
 		return netdev->ll_protocol->ll_addr_len;
 	}
+	if ( setting_cmp ( setting, &busid_setting ) == 0 ) {
+		dhcp_desc.type = desc->bus_type;
+		dhcp_desc.vendor = htons ( desc->vendor );
+		dhcp_desc.device = htons ( desc->device );
+		if ( len > sizeof ( dhcp_desc ) )
+			len = sizeof ( dhcp_desc );
+		memcpy ( data, &dhcp_desc, len );
+		return sizeof ( dhcp_desc );
+	}
 
 	return generic_settings_fetch ( settings, setting, data, len );
 }

src/net/udp/dhcp.c

 int dhcp_create_request ( struct dhcp_packet *dhcppkt,
 			  struct net_device *netdev, unsigned int msgtype,
 			  struct in_addr ciaddr, void *data, size_t max_len ) {
-	struct device_description *desc = &netdev->dev->desc;
 	struct dhcp_netdev_desc dhcp_desc;
 	struct dhcp_client_id client_id;
 	struct dhcp_client_uuid client_uuid;
 	}
 
 	/* Add options to identify the network device */
-	dhcp_desc.type = desc->bus_type;
-	dhcp_desc.vendor = htons ( desc->vendor );
-	dhcp_desc.device = htons ( desc->device );
+	fetch_setting ( &netdev->settings.settings, &busid_setting, &dhcp_desc,
+		sizeof ( dhcp_desc ) );
 	if ( ( rc = dhcppkt_store ( dhcppkt, DHCP_EB_BUS_ID, &dhcp_desc,
 				    sizeof ( dhcp_desc ) ) ) != 0 ) {
 		DBG ( "DHCP could not set bus ID option: %s\n",