Use net_device_operations structure and netdev_nullify() to allow for

safe dropping of the netdev ref by the driver while other refs still
exist.

Add netdev_irq() method.  Net device open()/close() methods should no
longer enable or disable IRQs.

Remove rx_quota; it wasn't used anywhere and added too much complexity
to implementing correct interrupt-masking behaviour in pxe_undi.c.

8 files changed, 290 insertions, 144 deletions

diff --git a/src/arch/i386/drivers/net/undinet.c b/src/arch/i386/drivers/net/undinet.c
index 46a759cc..3ed0ed64 100644
--- a/src/arch/i386/drivers/net/undinet.c
+++ b/src/arch/i386/drivers/net/undinet.c
@@ -394,7 +394,6 @@ static int undinet_transmit ( struct net_device *netdev,
  * Poll for received packets
  *
  * @v netdev		Network device
- * @v rx_quota		Maximum number of packets to receive
  *
  * Fun, fun, fun.  UNDI drivers don't use polling; they use
  * interrupts.  We therefore cheat and pretend that an interrupt has
@@ -412,7 +411,7 @@ static int undinet_transmit ( struct net_device *netdev,
  * of installing a genuine interrupt service routine and dealing with
  * the wonderful 8259 Programmable Interrupt Controller.  Joy.
  */
-static void undinet_poll ( struct net_device *netdev, unsigned int rx_quota ) {
+static void undinet_poll ( struct net_device *netdev ) {
 	struct undi_nic *undinic = netdev->priv;
 	struct s_PXENV_UNDI_ISR undi_isr;
 	struct io_buffer *iobuf = NULL;
@@ -454,7 +453,7 @@ static void undinet_poll ( struct net_device *netdev, unsigned int rx_quota ) {
 	}
 
 	/* Run through the ISR loop */
-	while ( rx_quota ) {
+	while ( 1 ) {
 		if ( ( rc = undinet_call ( undinic, PXENV_UNDI_ISR, &undi_isr,
 					   sizeof ( undi_isr ) ) ) != 0 )
 			break;
@@ -487,7 +486,6 @@ static void undinet_poll ( struct net_device *netdev, unsigned int rx_quota ) {
 				/* Whole packet received; deliver it */
 				netdev_rx ( netdev, iobuf );
 				iobuf = NULL;
-				--rx_quota;
 				/* Etherboot 5.4 fails to return all packets
 				 * under mild load; pretend it retriggered.
 				 */
@@ -600,6 +598,29 @@ static void undinet_close ( struct net_device *netdev ) {
 }
 
 /**
+ * Enable/disable interrupts
+ *
+ * @v netdev		Net device
+ * @v enable		Interrupts should be enabled
+ */
+static void undinet_irq ( struct net_device *netdev, int enable ) {
+	struct undi_nic *undinic = netdev->priv;
+
+	/* Cannot support interrupts yet */
+	DBGC ( undinic, "UNDINIC %p cannot %s interrupts\n",
+	       undinic, ( enable ? "enable" : "disable" ) );
+}
+
+/** UNDI network device operations */
+static struct net_device_operations undinet_operations = {
+	.open		= undinet_open,
+	.close		= undinet_close,
+	.transmit	= undinet_transmit,
+	.poll		= undinet_poll,
+	.irq   		= undinet_irq,
+};
+
+/**
  * Probe UNDI device
  *
  * @v undi		UNDI device
@@ -622,6 +643,7 @@ int undinet_probe ( struct undi_device *undi ) {
 	netdev = alloc_etherdev ( sizeof ( *undinic ) );
 	if ( ! netdev )
 		return -ENOMEM;
+	netdev_init ( netdev, &undinet_operations );
 	undinic = netdev->priv;
 	undi_set_drvdata ( undi, netdev );
 	netdev->dev = &undi->dev;
@@ -685,12 +707,6 @@ int undinet_probe ( struct undi_device *undi ) {
 		undinic->hacks |= UNDI_HACK_EB54;
 	}
 
-	/* Point to NIC specific routines */
-	netdev->open	 = undinet_open;
-	netdev->close	 = undinet_close;
-	netdev->transmit = undinet_transmit;
-	netdev->poll	 = undinet_poll;
-
 	/* Register network device */
 	if ( ( rc = register_netdev ( netdev ) ) != 0 )
 		goto err_register;
@@ -716,6 +732,7 @@ int undinet_probe ( struct undi_device *undi ) {
 	undinet_call ( undinic, PXENV_STOP_UNDI, &stop_undi,
 		       sizeof ( stop_undi ) );
  err_start_undi:
+	netdev_nullify ( netdev );
 	netdev_put ( netdev );
 	undi_set_drvdata ( undi, NULL );
 	return rc;
@@ -751,6 +768,7 @@ void undinet_remove ( struct undi_device *undi ) {
 	undi->flags &= ~UNDI_FL_STARTED;
 
 	/* Free network device */
+	netdev_nullify ( netdev );
 	netdev_put ( netdev );
 
 	DBGC ( undinic, "UNDINIC %p removed\n", undinic );
diff --git a/src/drivers/net/legacy.c b/src/drivers/net/legacy.c
index 2d4633d4..6ae2fbec 100644
--- a/src/drivers/net/legacy.c
+++ b/src/drivers/net/legacy.c
@@ -36,13 +36,10 @@ static int legacy_transmit ( struct net_device *netdev, struct io_buffer *iobuf
 	return 0;
 }
 
-static void legacy_poll ( struct net_device *netdev, unsigned int rx_quota ) {
+static void legacy_poll ( struct net_device *netdev ) {
 	struct nic *nic = netdev->priv;
 	struct io_buffer *iobuf;
 
-	if ( ! rx_quota )
-		return;
-
 	iobuf = alloc_iob ( ETH_FRAME_LEN );
 	if ( ! iobuf )
 		return;
@@ -57,19 +54,29 @@ static void legacy_poll ( struct net_device *netdev, unsigned int rx_quota ) {
 	}
 }
 
-static int legacy_open ( struct net_device *netdev ) {
-	struct nic *nic = netdev->priv;
-
-	nic->nic_op->irq ( nic, ENABLE );
+static int legacy_open ( struct net_device *netdev __unused ) {
+	/* Nothing to do */
 	return 0;
 }
 
-static void legacy_close ( struct net_device *netdev ) {
+static void legacy_close ( struct net_device *netdev __unused ) {
+	/* Nothing to do */
+}
+
+static void legacy_irq ( struct net_device *netdev __unused, int enable ) {
 	struct nic *nic = netdev->priv;
 
-	nic->nic_op->irq ( nic, DISABLE );
+	nic->nic_op->irq ( nic, ( enable ? ENABLE : DISABLE ) );
 }
 
+static struct net_device_operations legacy_operations = {
+	.open		= legacy_open,
+	.close		= legacy_close,
+	.transmit	= legacy_transmit,
+	.poll		= legacy_poll,
+	.irq   		= legacy_irq,
+};
+
 int legacy_probe ( void *hwdev,
 		   void ( * set_drvdata ) ( void *hwdev, void *priv ),
 		   struct device *dev,
@@ -84,27 +91,21 @@ int legacy_probe ( void *hwdev,
 	netdev = alloc_etherdev ( 0 );
 	if ( ! netdev )
 		return -ENOMEM;
+	netdev_init ( netdev, &legacy_operations );
 	netdev->priv = &nic;
 	memset ( &nic, 0, sizeof ( nic ) );
 	set_drvdata ( hwdev, netdev );
 	netdev->dev = dev;
 
-	netdev->open = legacy_open;
-	netdev->close = legacy_close;
-	netdev->transmit = legacy_transmit;
-	netdev->poll = legacy_poll;
 	nic.node_addr = netdev->ll_addr;
 
 	if ( ! probe ( &nic, hwdev ) ) {
-		netdev_put ( netdev );
-		return -ENODEV;
+		rc = -ENODEV;
+		goto err_probe;
 	}
 
-	if ( ( rc = register_netdev ( netdev ) ) != 0 ) {
-		disable ( &nic, hwdev );
-		netdev_put ( netdev );
-		return rc;
-	}
+	if ( ( rc = register_netdev ( netdev ) ) != 0 )
+		goto err_register;
 
 	/* Do not remove this message */
 	printf ( "WARNING: Using legacy NIC wrapper on %s\n",
@@ -112,6 +113,13 @@ int legacy_probe ( void *hwdev,
 
 	legacy_registered = 1;
 	return 0;
+
+ err_register:
+	disable ( &nic, hwdev );
+ err_probe:
+	netdev_nullify ( netdev );
+	netdev_put ( netdev );
+	return rc;
 }
 
 void legacy_remove ( void *hwdev,
@@ -122,6 +130,7 @@ void legacy_remove ( void *hwdev,
 
 	unregister_netdev ( netdev );
 	disable ( nic, hwdev );
+	netdev_nullify ( netdev );
 	netdev_put ( netdev );
 	legacy_registered = 0;
 }
diff --git a/src/drivers/net/pnic.c b/src/drivers/net/pnic.c
index 38b4af6d..b431ec52 100644
--- a/src/drivers/net/pnic.c
+++ b/src/drivers/net/pnic.c
@@ -112,35 +112,34 @@ static int pnic_api_check ( uint16_t api_version ) {
 /**************************************************************************
 POLL - Wait for a frame
 ***************************************************************************/
-static void pnic_poll ( struct net_device *netdev, unsigned int rx_quota ) {
+static void pnic_poll ( struct net_device *netdev ) {
 	struct pnic *pnic = netdev->priv;
 	struct io_buffer *iobuf;
 	uint16_t length;
 	uint16_t qlen;
 
 	/* Fetch all available packets */
-	while ( rx_quota ) {
+	while ( 1 ) {
 		if ( pnic_command ( pnic, PNIC_CMD_RECV_QLEN, NULL, 0,
 				    &qlen, sizeof ( qlen ), NULL )
 		     != PNIC_STATUS_OK )
-			break;
+			return;
 		if ( qlen == 0 )
-			break;
+			return;
 		iobuf = alloc_iob ( ETH_FRAME_LEN );
 		if ( ! iobuf ) {
 			DBG ( "could not allocate buffer\n" );
 			netdev_rx_err ( netdev, NULL, -ENOMEM );
-			break;
+			return;
 		}
 		if ( pnic_command ( pnic, PNIC_CMD_RECV, NULL, 0,
 				    iobuf->data, ETH_FRAME_LEN, &length )
 		     != PNIC_STATUS_OK ) {
 			netdev_rx_err ( netdev, iobuf, -EIO );
-			break;
+			return;
 		}
 		iob_put ( iobuf, length );
 		netdev_rx ( netdev, iobuf );
-		--rx_quota;
 	}
 }
 
@@ -164,30 +163,41 @@ static int pnic_transmit ( struct net_device *netdev, struct io_buffer *iobuf )
 /**************************************************************************
 OPEN - Open network device
 ***************************************************************************/
-static int pnic_open ( struct net_device *netdev ) {
-	struct pnic *pnic = netdev->priv;
-	static const uint8_t enable = 1;
-
-	/* Enable interrupts */
-	pnic_command ( pnic, PNIC_CMD_MASK_IRQ, &enable,
-		       sizeof ( enable ), NULL, 0, NULL );
-	
+static int pnic_open ( struct net_device *netdev __unused ) {
+	/* Nothing to do */
 	return 0;
 }
 
 /**************************************************************************
 CLOSE - Close network device
 ***************************************************************************/
-static void pnic_close ( struct net_device *netdev ) {
-	struct pnic *pnic = netdev->priv;
-	static const uint8_t disable = 0;
+static void pnic_close ( struct net_device *netdev __unused ) {
+	/* Nothing to do */
+}
 
-	/* Disable interrupts */
-	pnic_command ( pnic, PNIC_CMD_MASK_IRQ, &disable,
-		       sizeof ( disable ), NULL, 0, NULL );
+/**************************************************************************
+IRQ - Enable/disable interrupts
+***************************************************************************/
+static void pnic_irq ( struct net_device *netdev, int enable ) {
+	struct pnic *pnic = netdev->priv;
+	uint8_t mask = ( enable ? 1 : 0 );
+	
+	pnic_command ( pnic, PNIC_CMD_MASK_IRQ, &mask, sizeof ( mask ),
+		       NULL, 0, NULL );
 }
 
 /**************************************************************************
+OPERATIONS TABLE
+***************************************************************************/
+static struct net_device_operations pnic_operations = {
+	.open		= pnic_open,
+	.close		= pnic_close,
+	.transmit	= pnic_transmit,
+	.poll		= pnic_poll,
+	.irq   		= pnic_irq,
+};
+
+/**************************************************************************
 DISABLE - Turn off ethernet interface
 ***************************************************************************/
 static void pnic_remove ( struct pci_device *pci ) {
@@ -196,6 +206,7 @@ static void pnic_remove ( struct pci_device *pci ) {
 
 	unregister_netdev ( netdev );
 	pnic_command ( pnic, PNIC_CMD_RESET, NULL, 0, NULL, 0, NULL );
+	netdev_nullify ( netdev );
 	netdev_put ( netdev );
 }
 
@@ -214,6 +225,7 @@ static int pnic_probe ( struct pci_device *pci,
 	netdev = alloc_etherdev ( sizeof ( *pnic ) );
 	if ( ! netdev )
 		return -ENOMEM;
+	netdev_init ( netdev, &pnic_operations );
 	pnic = netdev->priv;
 	pci_set_drvdata ( pci, netdev );
 	netdev->dev = &pci->dev;
@@ -238,12 +250,6 @@ static int pnic_probe ( struct pci_device *pci,
 	status = pnic_command ( pnic, PNIC_CMD_READ_MAC, NULL, 0,
 				netdev->ll_addr, ETH_ALEN, NULL );
 
-	/* Point to NIC specific routines */
-	netdev->open	 = pnic_open;
-	netdev->close	 = pnic_close;
-	netdev->poll	 = pnic_poll;
-	netdev->transmit = pnic_transmit;
-
 	/* Register network device */
 	if ( ( rc = register_netdev ( netdev ) ) != 0 )
 		goto err;
@@ -252,6 +258,7 @@ static int pnic_probe ( struct pci_device *pci,
 
  err:
 	/* Free net device */
+	netdev_nullify ( netdev );
 	netdev_put ( netdev );
 	return rc;
 }
diff --git a/src/drivers/net/rtl8139.c b/src/drivers/net/rtl8139.c
index 54bda07f..8b40918f 100644
--- a/src/drivers/net/rtl8139.c
+++ b/src/drivers/net/rtl8139.c
@@ -302,12 +302,6 @@ static struct nvo_fragment rtl_nvo_fragments[] = {
  */
 static void rtl_reset ( struct rtl8139_nic *rtl ) {
 
-	/* Disable interrupts.  May not be necessary, but datasheet
-	 * doesn't say that the reset command also resets the
-	 * interrupt mask.
-	 */
-	outw ( 0, rtl->ioaddr + IntrMask );
-
 	/* Reset chip */
 	outb ( CmdReset, rtl->ioaddr + ChipCmd );
 	mdelay ( 10 );
@@ -346,9 +340,6 @@ static int rtl_open ( struct net_device *netdev ) {
 	outl ( ( ( TX_DMA_BURST << 8 ) | ( TX_IPG << 24 ) ),
 	       rtl->ioaddr + TxConfig );
 
-	/* Enable interrupts */
-	outw ( ( ROK | RER | TOK | TER ), rtl->ioaddr + IntrMask );
-
 	return 0;
 }
 
@@ -400,13 +391,12 @@ static int rtl_transmit ( struct net_device *netdev, struct io_buffer *iobuf ) {
 	return 0;
 }
 
-/** 
+/**
  * Poll for received packets
  *
  * @v netdev	Network device
- * @v rx_quota	Maximum number of packets to receive
  */
-static void rtl_poll ( struct net_device *netdev, unsigned int rx_quota ) {
+static void rtl_poll ( struct net_device *netdev ) {
 	struct rtl8139_nic *rtl = netdev->priv;
 	unsigned int status;
 	unsigned int tsad;
@@ -433,7 +423,7 @@ static void rtl_poll ( struct net_device *netdev, unsigned int rx_quota ) {
 	}
 
 	/* Handle received packets */
-	while ( rx_quota && ! ( inw ( rtl->ioaddr + ChipCmd ) & RxBufEmpty ) ){
+	while ( ! ( inw ( rtl->ioaddr + ChipCmd ) & RxBufEmpty ) ) {
 		rx_status = * ( ( uint16_t * )
 				( rtl->rx.ring + rtl->rx.offset ) );
 		rx_len = * ( ( uint16_t * )
@@ -461,7 +451,6 @@ static void rtl_poll ( struct net_device *netdev, unsigned int rx_quota ) {
 				 rtl->rx.ring, wrapped_len );
 
 			netdev_rx ( netdev, rx_iob );
-			rx_quota--;
 		} else {
 			DBG ( "RX bad packet (status %#04x len %d)\n",
 			      rx_status, rx_len );
@@ -474,6 +463,28 @@ static void rtl_poll ( struct net_device *netdev, unsigned int rx_quota ) {
 }
 
 /**
+ * Enable/disable interrupts
+ *
+ * @v netdev	Network device
+ * @v enable	Interrupts should be enabled
+ */
+static void rtl_irq ( struct net_device *netdev, int enable ) {
+	struct rtl8139_nic *rtl = netdev->priv;
+	
+	outw ( ( enable ? ( ROK | RER | TOK | TER ) : 0 ),
+	       rtl->ioaddr + IntrMask );
+}
+
+/** RTL8139 net device operations */
+static struct net_device_operations rtl_operations = {
+	.open		= rtl_open,
+	.close		= rtl_close,
+	.transmit	= rtl_transmit,
+	.poll		= rtl_poll,
+	.irq		= rtl_irq,
+};
+
+/**
  * Probe PCI device
  *
  * @v pci	PCI device
@@ -490,6 +501,7 @@ static int rtl_probe ( struct pci_device *pci,
 	netdev = alloc_etherdev ( sizeof ( *rtl ) );
 	if ( ! netdev )
 		return -ENOMEM;
+	netdev_init ( netdev, &rtl_operations );
 	rtl = netdev->priv;
 	pci_set_drvdata ( pci, netdev );
 	netdev->dev = &pci->dev;
@@ -504,12 +516,6 @@ static int rtl_probe ( struct pci_device *pci,
 	rtl_init_eeprom ( rtl );
 	nvs_read ( &rtl->eeprom.nvs, EE_MAC, netdev->ll_addr, ETH_ALEN );
 	
-	/* Point to NIC specific routines */
-	netdev->open	 = rtl_open;
-	netdev->close	 = rtl_close;
-	netdev->transmit = rtl_transmit;
-	netdev->poll	 = rtl_poll;
-
 	/* Register network device */
 	if ( ( rc = register_netdev ( netdev ) ) != 0 )
 		goto err_register_netdev;
@@ -526,6 +532,7 @@ static int rtl_probe ( struct pci_device *pci,
 	unregister_netdev ( netdev );
  err_register_netdev:
 	rtl_reset ( rtl );
+	netdev_nullify ( netdev );
 	netdev_put ( netdev );
 	return rc;
 }
@@ -543,6 +550,7 @@ static void rtl_remove ( struct pci_device *pci ) {
 		nvo_unregister ( &rtl->nvo );
 	unregister_netdev ( netdev );
 	rtl_reset ( rtl );
+	netdev_nullify ( netdev );
 	netdev_put ( netdev );
 }
 
diff --git a/src/include/gpxe/netdevice.h b/src/include/gpxe/netdevice.h
index d6b9a1be..d82c6d8f 100644
--- a/src/include/gpxe/netdevice.h
+++ b/src/include/gpxe/netdevice.h
@@ -128,41 +128,8 @@ struct ll_protocol {
 	const uint8_t *ll_broadcast;
 };
 
-/**
- * Network device statistics
- *
- */
-struct net_device_stats {
-	/** Count of successfully completed transmissions */
-	unsigned int tx_ok;
-	/** Count of transmission errors */
-	unsigned int tx_err;
-	/** Count of successfully received packets */
-	unsigned int rx_ok;
-	/** Count of reception errors */
-	unsigned int rx_err;
-};
-
-/**
- * A network device
- *
- * This structure represents a piece of networking hardware.  It has
- * properties such as a link-layer address and methods for
- * transmitting and receiving raw packets.
- *
- * Note that this structure must represent a generic network device,
- * not just an Ethernet device.
- */
-struct net_device {
-	/** Reference counter */
-	struct refcnt refcnt;
-	/** List of network devices */
-	struct list_head list;
-	/** Name of this network device */
-	char name[8];
-	/** Underlying hardware device */
-	struct device *dev;
-
+/** Network device operations */
+struct net_device_operations {
 	/** Open network device
 	 *
 	 * @v netdev	Network device
@@ -199,20 +166,62 @@ struct net_device {
 	 * This method is guaranteed to be called only when the device
 	 * is open.
 	 */
-	int ( * transmit ) ( struct net_device *netdev, struct io_buffer *iobuf );
-	/** Poll for received packet
+	int ( * transmit ) ( struct net_device *netdev,
+			     struct io_buffer *iobuf );
+	/** Poll for completed and received packets
 	 *
 	 * @v netdev	Network device
-	 * @v rx_quota	Maximum number of packets to receive
 	 *
-	 * This method should cause the hardware to check for received
-	 * packets.  Any received packets should be delivered via
-	 * netdev_rx(), up to a maximum of @c rx_quota packets.
+	 * This method should cause the hardware to check for
+	 * completed transmissions and received packets.  Any received
+	 * packets should be delivered via netdev_rx().
 	 *
 	 * This method is guaranteed to be called only when the device
 	 * is open.
 	 */
-	void ( * poll ) ( struct net_device *netdev, unsigned int rx_quota );
+	void ( * poll ) ( struct net_device *netdev );
+	/** Enable or disable interrupts
+	 *
+	 * @v netdev	Network device
+	 * @v enable	Interrupts should be enabled
+	 */
+	void ( * irq ) ( struct net_device *netdev, int enable );
+};
+
+/** Network device statistics */
+struct net_device_stats {
+	/** Count of successfully completed transmissions */
+	unsigned int tx_ok;
+	/** Count of transmission errors */
+	unsigned int tx_err;
+	/** Count of successfully received packets */
+	unsigned int rx_ok;
+	/** Count of reception errors */
+	unsigned int rx_err;
+};
+
+/**
+ * A network device
+ *
+ * This structure represents a piece of networking hardware.  It has
+ * properties such as a link-layer address and methods for
+ * transmitting and receiving raw packets.
+ *
+ * Note that this structure must represent a generic network device,
+ * not just an Ethernet device.
+ */
+struct net_device {
+	/** Reference counter */
+	struct refcnt refcnt;
+	/** List of network devices */
+	struct list_head list;
+	/** Name of this network device */
+	char name[8];
+	/** Underlying hardware device */
+	struct device *dev;
+
+	/** Network device operations */
+	struct net_device_operations *op;
 
 	/** Link-layer protocol */
 	struct ll_protocol *ll_protocol;
@@ -248,6 +257,30 @@ struct net_device {
 #define __net_protocol __table ( struct net_protocol, net_protocols, 01 )
 
 extern struct list_head net_devices;
+extern struct net_device_operations null_netdev_operations;
+
+/**
+ * Initialise a network device
+ *
+ * @v netdev		Network device
+ * @v op		Network device operations
+ */
+static inline void netdev_init ( struct net_device *netdev,
+				 struct net_device_operations *op ) {
+	netdev->op = op;
+}
+
+/**
+ * Stop using a network device
+ *
+ * @v netdev		Network device
+ *
+ * Drivers should call this method immediately before the final call
+ * to netdev_put().
+ */
+static inline void netdev_nullify ( struct net_device *netdev ) {
+	netdev->op = &null_netdev_operations;
+}
 
 /**
  * Get printable network device hardware address
@@ -300,13 +333,14 @@ extern void netdev_tx_complete_next_err ( struct net_device *netdev, int rc );
 extern void netdev_rx ( struct net_device *netdev, struct io_buffer *iobuf );
 extern void netdev_rx_err ( struct net_device *netdev,
 			    struct io_buffer *iobuf, int rc );
-extern int netdev_poll ( struct net_device *netdev, unsigned int rx_quota );
+extern void netdev_poll ( struct net_device *netdev );
 extern struct io_buffer * netdev_rx_dequeue ( struct net_device *netdev );
 extern struct net_device * alloc_netdev ( size_t priv_size );
 extern int register_netdev ( struct net_device *netdev );
 extern int netdev_open ( struct net_device *netdev );
 extern void netdev_close ( struct net_device *netdev );
 extern void unregister_netdev ( struct net_device *netdev );
+extern void netdev_irq ( struct net_device *netdev, int enable );
 extern struct net_device * find_netdev ( const char *name );
 extern struct net_device * find_netdev_by_location ( unsigned int bus_type,
 						     unsigned int location );
diff --git a/src/interface/pxe/pxe_undi.c b/src/interface/pxe/pxe_undi.c
index cc23de70..f19dfcc5 100644
--- a/src/interface/pxe/pxe_undi.c
+++ b/src/interface/pxe/pxe_undi.c
@@ -69,7 +69,13 @@ void pxe_set_netdev ( struct net_device *netdev ) {
  * @ret rc		Return status code
  */
 static int pxe_netdev_open ( void ) {
-	return netdev_open ( pxe_netdev );
+	int rc;
+
+	if ( ( rc = netdev_open ( pxe_netdev ) ) != 0 )
+		return rc;
+
+	netdev_irq ( pxe_netdev, 1 );
+	return 0;
 }
 
 /**
@@ -77,6 +83,7 @@ static int pxe_netdev_open ( void ) {
  *
  */
 static void pxe_netdev_close ( void ) {
+	netdev_irq ( pxe_netdev, 0 );
 	netdev_close ( pxe_netdev );
 	undi_tx_count = 0;
 }
@@ -543,14 +550,13 @@ PXENV_EXIT_t pxenv_undi_isr ( struct s_PXENV_UNDI_ISR *undi_isr ) {
 		/* Call poll().  This should acknowledge the device
 		 * interrupt and queue up any received packet.
 		 */
-		if ( netdev_poll ( pxe_netdev, -1U ) ) {
-			/* Packet waiting in queue */
-			DBG ( " OURS" );
-			undi_isr->FuncFlag = PXENV_UNDI_ISR_OUT_OURS;
-		} else {
-			DBG ( " NOT_OURS" );
-			undi_isr->FuncFlag = PXENV_UNDI_ISR_OUT_NOT_OURS;
-		}
+		netdev_poll ( pxe_netdev );
+
+		/* Disable interrupts to avoid interrupt storm */
+		netdev_irq ( pxe_netdev, 0 );
+
+		/* Always say it was ours for the sake of simplicity */
+		undi_isr->FuncFlag = PXENV_UNDI_ISR_OUT_OURS;
 		break;
 	case PXENV_UNDI_ISR_IN_PROCESS :
 	case PXENV_UNDI_ISR_IN_GET_NEXT :
@@ -570,6 +576,8 @@ PXENV_EXIT_t pxenv_undi_isr ( struct s_PXENV_UNDI_ISR *undi_isr ) {
 		if ( ! iobuf ) {
 			/* No more packets remaining */
 			undi_isr->FuncFlag = PXENV_UNDI_ISR_OUT_DONE;
+			/* Re-enable interrupts */
+			netdev_irq ( pxe_netdev, 1 );
 			break;
 		}
 
diff --git a/src/net/netdevice.c b/src/net/netdevice.c
index d72392ca..460de89c 100644
--- a/src/net/netdevice.c
+++ b/src/net/netdevice.c
@@ -68,7 +68,7 @@ int netdev_tx ( struct net_device *netdev, struct io_buffer *iobuf ) {
 		goto err;
 	}
 		
-	if ( ( rc = netdev->transmit ( netdev, iobuf ) ) != 0 )
+	if ( ( rc = netdev->op->transmit ( netdev, iobuf ) ) != 0 )
 		goto err;
 
 	return 0;
@@ -187,22 +187,18 @@ void netdev_rx_err ( struct net_device *netdev,
 }
 
 /**
- * Poll for packet on network device
+ * Poll for completed and received packets on network device
  *
  * @v netdev		Network device
- * @v rx_quota		Maximum number of packets to receive
- * @ret True		There are packets present in the receive queue
- * @ret False		There are no packets present in the receive queue
  *
- * Polls the network device for received packets.  Any received
- * packets will be added to the RX packet queue via netdev_rx().
+ * Polls the network device for completed transmissions and received
+ * packets.  Any received packets will be added to the RX packet queue
+ * via netdev_rx().
  */
-int netdev_poll ( struct net_device *netdev, unsigned int rx_quota ) {
+void netdev_poll ( struct net_device *netdev ) {
 
 	if ( netdev->state & NETDEV_OPEN )
-		netdev->poll ( netdev, rx_quota );
-
-	return ( ! list_empty ( &netdev->rx_queue ) );
+		netdev->op->poll ( netdev );
 }
 
 /**
@@ -317,7 +313,7 @@ int netdev_open ( struct net_device *netdev ) {
 	DBGC ( netdev, "NETDEV %p opening\n", netdev );
 
 	/* Open the device */
-	if ( ( rc = netdev->open ( netdev ) ) != 0 )
+	if ( ( rc = netdev->op->open ( netdev ) ) != 0 )
 		return rc;
 
 	/* Mark as opened */
@@ -339,7 +335,7 @@ void netdev_close ( struct net_device *netdev ) {
 	DBGC ( netdev, "NETDEV %p closing\n", netdev );
 
 	/* Close the device */
-	netdev->close ( netdev );
+	netdev->op->close ( netdev );
 
 	/* Flush TX and RX queues */
 	netdev_tx_flush ( netdev );
@@ -367,6 +363,15 @@ void unregister_netdev ( struct net_device *netdev ) {
 	DBGC ( netdev, "NETDEV %p unregistered\n", netdev );
 }
 
+/** Enable or disable interrupts
+ *
+ * @v netdev		Network device
+ * @v enable		Interrupts should be enabled
+ */
+void netdev_irq ( struct net_device *netdev, int enable ) {
+	netdev->op->irq ( netdev, enable );
+}
+
 /**
  * Get network device by name
  *
@@ -462,7 +467,7 @@ static void net_step ( struct process *process __unused ) {
 	list_for_each_entry ( netdev, &net_devices, list ) {
 
 		/* Poll for new packets */
-		netdev_poll ( netdev, -1U );
+		netdev_poll ( netdev );
 
 		/* Process at most one received packet.  Give priority
 		 * to getting packets out of the NIC over processing
diff --git a/src/net/nullnet.c b/src/net/nullnet.c
new file mode 100644
index 00000000..4b6ba4c1
--- /dev/null
+++ b/src/net/nullnet.c
@@ -0,0 +1,57 @@
+/*
+ * Copyright (C) 2006 Michael Brown <mbrown@fensystems.co.uk>.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+#include <stdint.h>
+#include <gpxe/iobuf.h>
+#include <gpxe/netdevice.h>
+
+/** @file
+ *
+ * Null network device
+ *
+ */
+
+static int null_open ( struct net_device *netdev __unused ) {
+	return -ENODEV;
+};
+
+static void null_close ( struct net_device *netdev __unused ) {
+	/* Do nothing */
+};
+
+static int null_transmit ( struct net_device *netdev __unused,
+			   struct io_buffer *iobuf __unused ) {
+	return -ENODEV;
+};
+
+static void null_poll ( struct net_device *netdev __unused ) {
+	/* Do nothing */
+}
+
+static void null_irq ( struct net_device *netdev __unused,
+		       int enable __unused ) {
+	/* Do nothing */
+}
+
+struct net_device_operations null_netdev_operations = {
+	.open		= null_open,
+	.close		= null_close,
+	.transmit	= null_transmit,
+	.poll		= null_poll,
+	.irq   		= null_irq,
+};