[netdevice] Add the concept of an "Ethernet-compatible" MAC address

The iBFT is Ethernet-centric in providing only six bytes for a MAC
address.  This is most probably an indirect consequence of a similar
design flaw in the Windows NDIS stack.  (The WinOF IPoIB stack
performs all sorts of contortions in order to pretend to the NDIS
layer that it is dealing with six-byte MAC addresses.)

There is no sensible way in which to extend the iBFT without breaking
compatibility with programs that expect to parse it.  Add the notion
of an "Ethernet-compatible" MAC address to our link layer abstraction,
so that link layers can provide their own workarounds for this
limitation.

src/drivers/net/ipoib.c

 	return -ENOTSUP;
 }
 
+/**
+ * Generate Mellanox Ethernet-compatible compressed link-layer address
+ *
+ * @v ll_addr		Link-layer address
+ * @v eth_addr		Ethernet-compatible address to fill in
+ */
+static int ipoib_mlx_eth_addr ( const struct ib_gid_half *guid,
+				uint8_t *eth_addr ) {
+	eth_addr[0] = ( ( guid->u.bytes[3] == 2 ) ? 0x00 : 0x02 );
+	eth_addr[1] = guid->u.bytes[1];
+	eth_addr[2] = guid->u.bytes[2];
+	eth_addr[3] = guid->u.bytes[5];
+	eth_addr[4] = guid->u.bytes[6];
+	eth_addr[5] = guid->u.bytes[7];
+	return 0;
+}
+
+/** An IPoIB Ethernet-compatible compressed link-layer address generator */
+struct ipoib_eth_addr_handler {
+	/** GUID byte 1 */
+	uint8_t byte1;
+	/** GUID byte 2 */
+	uint8_t byte2;
+	/** Handler */
+	int ( * eth_addr ) ( const struct ib_gid_half *guid,
+			     uint8_t *eth_addr );
+};
+
+/** IPoIB Ethernet-compatible compressed link-layer address generators */
+static struct ipoib_eth_addr_handler ipoib_eth_addr_handlers[] = {
+	{ 0x02, 0xc9, ipoib_mlx_eth_addr },
+};
+
+/**
+ * Generate Ethernet-compatible compressed link-layer address
+ *
+ * @v ll_addr		Link-layer address
+ * @v eth_addr		Ethernet-compatible address to fill in
+ */
+static int ipoib_eth_addr ( const void *ll_addr, void *eth_addr ) {
+	const struct ipoib_mac *ipoib_addr = ll_addr;
+	const struct ib_gid_half *guid = &ipoib_addr->gid.u.half[1];
+	struct ipoib_eth_addr_handler *handler;
+	unsigned int i;
+
+	for ( i = 0 ; i < ( sizeof ( ipoib_eth_addr_handlers ) /
+			    sizeof ( ipoib_eth_addr_handlers[0] ) ) ; i++ ) {
+		handler = &ipoib_eth_addr_handlers[i];
+		if ( ( handler->byte1 == guid->u.bytes[1] ) &&
+		     ( handler->byte2 == guid->u.bytes[2] ) ) {
+			return handler->eth_addr ( guid, eth_addr );
+		}
+	}
+	return -ENOTSUP;
+}
+
 /** IPoIB protocol */
 struct ll_protocol ipoib_protocol __ll_protocol = {
 	.name		= "IPoIB",
 	.init_addr	= ipoib_init_addr,
 	.ntoa		= ipoib_ntoa,
 	.mc_hash	= ipoib_mc_hash,
+	.eth_addr	= ipoib_eth_addr,
 };
 
 /**

src/include/gpxe/ethernet.h

 extern const char * eth_ntoa ( const void *ll_addr );
 extern int eth_mc_hash ( unsigned int af, const void *net_addr,
 			 void *ll_addr );
+extern int eth_eth_addr ( const void *ll_addr, void *eth_addr );
 extern struct net_device * alloc_etherdev ( size_t priv_size );
 
 #endif /* _GPXE_ETHERNET_H */

src/include/gpxe/netdevice.h

 	/**
 	 * Transcribe link-layer address
 	 *
-	 * @v ll_addr	Link-layer address
-	 * @ret string	Human-readable transcription of address
+	 * @v ll_addr		Link-layer address
+	 * @ret string		Human-readable transcription of address
 	 *
 	 * This method should convert the link-layer address into a
 	 * human-readable format.
 	/**
 	 * Hash multicast address
 	 *
-	 * @v af	Address family
-	 * @v net_addr	Network-layer address
-	 * @v ll_addr	Link-layer address to fill in
-	 * @ret rc	Return status code
+	 * @v af		Address family
+	 * @v net_addr		Network-layer address
+	 * @v ll_addr		Link-layer address to fill in
+	 * @ret rc		Return status code
 	 */
 	int ( * mc_hash ) ( unsigned int af, const void *net_addr,
 			    void *ll_addr );
+	/**
+	 * Generate Ethernet-compatible compressed link-layer address
+	 *
+	 * @v ll_addr		Link-layer address
+	 * @v eth_addr		Ethernet-compatible address to fill in
+	 */
+	int ( * eth_addr ) ( const void *ll_addr, void *eth_addr );
 	/** Link-layer protocol
 	 *
 	 * This is an ARPHRD_XXX constant, in network byte order.

src/net/80211/net80211.c

 	.init_addr = eth_init_addr,
 	.ntoa = eth_ntoa,
 	.mc_hash = eth_mc_hash,
+	.eth_addr = eth_eth_addr,
 	.ll_proto = htons ( ARPHRD_ETHER ),	/* "encapsulated Ethernet" */
 	.hw_addr_len = ETH_ALEN,
 	.ll_addr_len = ETH_ALEN,

src/net/ethernet.c

 	}
 }
 
+/**
+ * Generate Ethernet-compatible compressed link-layer address
+ *
+ * @v ll_addr		Link-layer address
+ * @v eth_addr		Ethernet-compatible address to fill in
+ */
+int eth_eth_addr ( const void *ll_addr, void *eth_addr ) {
+	memcpy ( eth_addr, ll_addr, ETH_ALEN );
+	return 0;
+}
+
 /** Ethernet protocol */
 struct ll_protocol ethernet_protocol __ll_protocol = {
 	.name		= "Ethernet",
 	.init_addr	= eth_init_addr,
 	.ntoa		= eth_ntoa,
 	.mc_hash	= eth_mc_hash,
+	.eth_addr	= eth_eth_addr,
 };
 
 /**