[settings] Formalise notion of setting applicability

Expose a function setting_applies() to allow a caller to determine
whether or not a particular setting is applicable to a particular
settings block.

Restrict DHCP-backed settings blocks to accepting only DHCP-based
settings.

Restrict network device settings blocks to accepting only DHCP-based
settings and network device-specific settings such as "mac".

Inspired-by: Glenn Brown <glenn@myri.com>
Signed-off-by: Michael Brown <mcb30@ipxe.org>

1 files changed, 32 insertions, 0 deletions

diff --git a/src/include/ipxe/netdevice.h b/src/include/ipxe/netdevice.h
index ac7cec521..e49191f4a 100644
--- a/src/include/ipxe/netdevice.h
+++ b/src/include/ipxe/netdevice.h
@@ -390,6 +390,38 @@ struct net_driver {
 /** Declare a network driver */
 #define __net_driver __table_entry ( NET_DRIVERS, 01 )
 
+/** Network device setting tag magic
+ *
+ * All DHCP option settings are deemed to be valid as network device
+ * settings.  There are also some extra non-DHCP settings (such as
+ * "mac"), which are marked as being valid network device settings by
+ * using a magic tag value.
+ */
+#define NETDEV_SETTING_TAG_MAGIC 0xeb
+
+/**
+ * Construct network device setting tag
+ *
+ * @v id		Unique identifier
+ * @ret tag		Setting tag
+ */
+#define NETDEV_SETTING_TAG( id ) ( ( NETDEV_SETTING_TAG_MAGIC << 24 ) | (id) )
+
+/**
+ * Check if tag is a network device setting tag
+ *
+ * @v tag		Setting tag
+ * @ret is_ours		Tag is a network device setting tag
+ */
+#define IS_NETDEV_SETTING_TAG( tag ) \
+	( ( (tag) >> 24 ) == NETDEV_SETTING_TAG_MAGIC )
+
+/** MAC address setting tag */
+#define NETDEV_SETTING_TAG_MAC NETDEV_SETTING_TAG ( 0x01 )
+
+/** Bus ID setting tag */
+#define NETDEV_SETTING_TAG_BUS_ID NETDEV_SETTING_TAG ( 0x02 )
+
 extern struct list_head net_devices;
 extern struct net_device_operations null_netdev_operations;
 extern struct settings_operations netdev_settings_operations;