[virtio] Use host-specified MTU when available

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/drivers/net/virtio-net.c

 	QUEUE_NB
 };
 
-enum {
-	/** Max number of pending rx packets */
-	NUM_RX_BUF = 8,
-
-	/** Max Ethernet frame length, including FCS and VLAN tag */
-	RX_BUF_SIZE = 1522,
-};
+/** Max number of pending rx packets */
+#define NUM_RX_BUF 8
 
 struct virtnet_nic {
 	/** Base pio register address */
  */
 static void virtnet_refill_rx_virtqueue ( struct net_device *netdev ) {
 	struct virtnet_nic *virtnet = netdev->priv;
+	size_t len = ( netdev->max_pkt_len + 4 /* VLAN */ );
 
 	while ( virtnet->rx_num_iobufs < NUM_RX_BUF ) {
 		struct io_buffer *iobuf;
 
 		/* Try to allocate a buffer, stop for now if out of memory */
-		iobuf = alloc_iob ( RX_BUF_SIZE );
+		iobuf = alloc_iob ( len );
 		if ( ! iobuf )
 			break;
 
 		list_add ( &iobuf->list, &virtnet->rx_iobufs );
 
 		/* Mark packet length until we know the actual size */
-		iob_put ( iobuf, RX_BUF_SIZE );
+		iob_put ( iobuf, len );
 
 		virtnet_enqueue_iob ( netdev, RX_INDEX, iobuf );
 		virtnet->rx_num_iobufs++;
 
 	/* Driver is ready */
 	features = vp_get_features ( ioaddr );
-	vp_set_features ( ioaddr, features & ( 1 << VIRTIO_NET_F_MAC ) );
+	vp_set_features ( ioaddr, features & ( ( 1 << VIRTIO_NET_F_MAC ) |
+					       ( 1 << VIRTIO_NET_F_MTU ) ) );
 	vp_set_status ( ioaddr, VIRTIO_CONFIG_S_DRIVER | VIRTIO_CONFIG_S_DRIVER_OK );
 	return 0;
 }
 	}
 	vpm_set_features ( &virtnet->vdev, features & (
 		( 1ULL << VIRTIO_NET_F_MAC ) |
+		( 1ULL << VIRTIO_NET_F_MTU ) |
 		( 1ULL << VIRTIO_F_VERSION_1 ) |
 		( 1ULL << VIRTIO_F_ANY_LAYOUT ) ) );
 	vpm_add_status ( &virtnet->vdev, VIRTIO_CONFIG_S_FEATURES_OK );
 		virtnet->rx_num_iobufs--;
 
 		/* Update iobuf length */
-		iob_unput ( iobuf, RX_BUF_SIZE );
+		iob_unput ( iobuf, iob_len ( iobuf ) );
 		iob_put ( iobuf, len - sizeof ( struct virtio_net_hdr ) );
 
 		DBGC2 ( virtnet, "VIRTIO-NET %p rx complete iobuf %p len %zd\n",
 	struct net_device *netdev;
 	struct virtnet_nic *virtnet;
 	u32 features;
+	u16 mtu;
 	int rc;
 
 	/* Allocate and hook up net device */
 	adjust_pci_device ( pci );
 	vp_reset ( ioaddr );
 
-	/* Load MAC address */
+	/* Load MAC address and MTU */
 	features = vp_get_features ( ioaddr );
 	if ( features & ( 1 << VIRTIO_NET_F_MAC ) ) {
 		vp_get ( ioaddr, offsetof ( struct virtio_net_config, mac ),
 		DBGC ( virtnet, "VIRTIO-NET %p mac=%s\n", virtnet,
 		       eth_ntoa ( netdev->hw_addr ) );
 	}
+	if ( features & ( 1ULL << VIRTIO_NET_F_MTU ) ) {
+		vp_get ( ioaddr, offsetof ( struct virtio_net_config, mtu ),
+			 &mtu, sizeof ( mtu ) );
+		DBGC ( virtnet, "VIRTIO-NET %p mtu=%d\n", virtnet, mtu );
+		netdev->max_pkt_len = ( mtu + ETH_HLEN );
+	}
 
 	/* Register network device */
 	if ( ( rc = register_netdev ( netdev ) ) != 0 )
 	struct net_device *netdev;
 	struct virtnet_nic *virtnet;
 	u64 features;
+	u16 mtu;
 	int rc, common, isr, notify, config, device;
 
 	common = virtio_pci_find_capability ( pci, VIRTIO_PCI_CAP_COMMON_CFG );
 	vpm_add_status ( &virtnet->vdev, VIRTIO_CONFIG_S_ACKNOWLEDGE );
 	vpm_add_status ( &virtnet->vdev, VIRTIO_CONFIG_S_DRIVER );
 
-	/* Load MAC address */
+	/* Load MAC address and MTU */
 	if ( device ) {
 		features = vpm_get_features ( &virtnet->vdev );
 		if ( features & ( 1ULL << VIRTIO_NET_F_MAC ) ) {
 			DBGC ( virtnet, "VIRTIO-NET %p mac=%s\n", virtnet,
 			       eth_ntoa ( netdev->hw_addr ) );
 		}
+		if ( features & ( 1ULL << VIRTIO_NET_F_MTU ) ) {
+			vpm_get ( &virtnet->vdev,
+				  offsetof ( struct virtio_net_config, mtu ),
+				  &mtu, sizeof ( mtu ) );
+			DBGC ( virtnet, "VIRTIO-NET %p mtu=%d\n", virtnet,
+			       mtu );
+			netdev->max_pkt_len = ( mtu + ETH_HLEN );
+		}
 	}
 
 	/* We need a valid MAC address */

src/drivers/net/virtio-net.h

 /* The feature bitmap for virtio net */
 #define VIRTIO_NET_F_CSUM       0       /* Host handles pkts w/ partial csum */
 #define VIRTIO_NET_F_GUEST_CSUM 1       /* Guest handles pkts w/ partial csum */
+#define VIRTIO_NET_F_MTU        3       /* Initial MTU advice */
 #define VIRTIO_NET_F_MAC        5       /* Host has given MAC address. */
 #define VIRTIO_NET_F_GSO        6       /* Host handles pkts w/ any GSO type */
 #define VIRTIO_NET_F_GUEST_TSO4 7       /* Guest can handle TSOv4 in. */
 {
    /* The config defining mac address (if VIRTIO_NET_F_MAC) */
    u8 mac[6];
+   /* See VIRTIO_NET_F_STATUS and VIRTIO_NET_S_* above */
+   u16 status;
+   /* Maximum number of each of transmit and receive queues;
+    * see VIRTIO_NET_F_MQ and VIRTIO_NET_CTRL_MQ.
+    * Legal values are between 1 and 0x8000
+    */
+   u16 max_virtqueue_pairs;
+   /* Default maximum transmit unit advice */
+   u16 mtu;
 } __attribute__((packed));
 
 /* This is the first element of the scatter-gather list.  If you don't