TUN/TAP driver packet queuing fixes and improvements

Patch from Harald Roelle <harald.roelle@nm.ifi.lmu.de>

Fixes for the following issues
- "Kicking" packet behavior in case of kernel packet scheduler (! TUN_ONE_QUEUE):
  When the netif queue is stopped because of an overrun of the driver's queue,
  no new packets are delivered to the driver until a new packet arrives, not even
  when in the meantime there's again space in the driver's queue (gained by a
  reading user process). In short, whenever netif queue was stopped, one needs an
  additional packet to "kick" packet delivery to the driver.
  The reason for this is, that the netif queue is started but not woken up, i.e.
  the rest of the kernel is not signaled to resume packet delivery.

- Adjustment of tx queue length by ifconfig has only effect when TUN_ONE_QUEUE
  is set.  Otherwise always constant TUN_READQ_SIZE queue length is used.

- TX queue default length setting is not consistent:
  o TAP dev + TUN_ONE_QUEUE: 1000 (by ether_setup())
  o all other cases: 10

- Default tx queue length is too short in many cases.
  IMHO it should be at least twice as long as the number of fragments needed
  for a maximum sized IP packet at a "typical" MTU size.
  This would ensure that at least one complete IP packet can be delivered
  to the attached user space process, even if the packet's fragments
  are "misaligned" in the buffer and the user process is not scheduled
  in time to read the queue.

Additional modifications:

- To signal that stopping of the queue has occurred, the tx fifo overrun
  counter is increased.

- Implemented ethtool api. Primarily added to have a standard method requesting
  the driver version.
Signed-off-by: Max Krasnyansky <maxk@qualcomm.com>

drivers/net/tun.c

@@ -16,11 +16,22 @@
  */
 
 /*
+ *  Changes:
+ *
+ *  Harald Roelle <harald.roelle@ifi.lmu.de>  2004/04/20
+ *    Fixes in packet dropping, queue length setting and queue wakeup.
+ *    Increased default tx queue length.
+ *    Added ethtool API.
+ *    Minor cleanups
+ *
  *  Daniel Podlejski <underley@underley.eu.org>
  *    Modifications for 2.3.99-pre5 kernel.
  */
 
-#define TUN_VER "1.5"
+#define DRV_NAME	"tun"
+#define DRV_VERSION	"1.6"
+#define DRV_DESCRIPTION	"Universal TUN/TAP device driver"
+#define DRV_COPYRIGHT	"(C) 1999-2004 Max Krasnyansky <maxk@qualcomm.com>"
 
 #include <linux/config.h>
 #include <linux/module.h>
@@ -36,6 +47,7 @@
 #include <linux/netdevice.h>
 #include <linux/etherdevice.h>
 #include <linux/miscdevice.h>
+#include <linux/ethtool.h>
 #include <linux/rtnetlink.h>
 #include <linux/if.h>
 #include <linux/if_arp.h>
@@ -52,6 +64,7 @@ static int debug;
 /* Network device part of the driver */
 
 static LIST_HEAD(tun_dev_list);
+static struct ethtool_ops tun_ethtool_ops;
 
 /* Net device open. */
 static int tun_net_open(struct net_device *dev)
@@ -78,18 +91,24 @@ static int tun_net_xmit(struct sk_buff *skb, struct net_device *dev)
 	if (!tun->attached)
 		goto drop;
 
-	/* Queue packet */
-	if (!(tun->flags & TUN_ONE_QUEUE)) {
-		/* Normal queueing mode.
-		 * Packet scheduler handles dropping. */
-		if (skb_queue_len(&tun->readq) >= TUN_READQ_SIZE)
+	/* Packet dropping */
+	if (skb_queue_len(&tun->readq) >= dev->tx_queue_len) {
+		if (!(tun->flags & TUN_ONE_QUEUE)) {
+			/* Normal queueing mode. */
+			/* Packet scheduler handles dropping of further packets. */
 			netif_stop_queue(dev);
-	} else {
-		/* Single queue mode.
-		 * Driver handles dropping itself. */
-		if (skb_queue_len(&tun->readq) >= dev->tx_queue_len)
+
+			/* We won't see all dropped packets individually, so overrun
+			 * error is more appropriate. */
+			tun->stats.tx_fifo_errors++;
+		} else {
+			/* Single queue mode.
+			 * Driver handles dropping of all packets itself. */
 			goto drop;
+		}
 	}
+
+	/* Queue packet */
 	skb_queue_tail(&tun->readq, skb);
 
 	/* Notify and wake up reader process */
@@ -132,7 +151,7 @@ static void tun_net_init(struct net_device *dev)
 		/* Zero header length */
 		dev->type = ARPHRD_NONE; 
 		dev->flags = IFF_POINTOPOINT | IFF_NOARP | IFF_MULTICAST;
-		dev->tx_queue_len = 10;
+		dev->tx_queue_len = TUN_READQ_SIZE;  /* We prefer our own queue length */
 		break;
 
 	case TUN_TAP_DEV:
@@ -144,6 +163,7 @@ static void tun_net_init(struct net_device *dev)
 		get_random_bytes(dev->dev_addr + sizeof(u16), 4);
 
 		ether_setup(dev);
+		dev->tx_queue_len = TUN_READQ_SIZE;  /* We prefer our own queue length */
 		break;
 	}
 }
@@ -318,7 +338,7 @@ static ssize_t tun_chr_readv(struct file *file, const struct iovec *iv,
 			schedule();
 			continue;
 		}
-		netif_start_queue(tun->dev);
+		netif_wake_queue(tun->dev);
 
 		ret = tun_put_user(tun, skb, (struct iovec *) iv, len);
 
@@ -354,6 +374,7 @@ static void tun_setup(struct net_device *dev)
 	dev->hard_start_xmit = tun_net_xmit;
 	dev->stop = tun_net_close;
 	dev->get_stats = tun_net_stats;
+	dev->ethtool_ops = &tun_ethtool_ops;
 	dev->destructor = free_netdev;
 }
 
@@ -608,12 +629,97 @@ static struct miscdevice tun_miscdev = {
 	.devfs_name = "net/tun",
 };
 
+/* ethtool interface */
+
+static int tun_get_settings(struct net_device *dev, struct ethtool_cmd *cmd)
+{
+	cmd->supported		= 0;
+	cmd->advertising	= 0;
+	cmd->speed		= SPEED_10;
+	cmd->duplex		= DUPLEX_FULL;
+	cmd->port		= PORT_TP;
+	cmd->phy_address	= 0;
+	cmd->transceiver	= XCVR_INTERNAL;
+	cmd->autoneg		= AUTONEG_DISABLE;
+	cmd->maxtxpkt		= 0;
+	cmd->maxrxpkt		= 0;
+	return 0;
+}
+
+static void tun_get_drvinfo(struct net_device *dev, struct ethtool_drvinfo *info)
+{
+	struct tun_struct *tun = netdev_priv(dev);
+
+	strcpy(info->driver, DRV_NAME);
+	strcpy(info->version, DRV_VERSION);
+	strcpy(info->fw_version, "N/A");
+
+	switch (tun->flags & TUN_TYPE_MASK) {
+	case TUN_TUN_DEV:
+		strcpy(info->bus_info, "tun");
+		break;
+	case TUN_TAP_DEV:
+		strcpy(info->bus_info, "tap");
+		break;
+	}
+}
+
+static u32 tun_get_msglevel(struct net_device *dev)
+{
+#ifdef TUN_DEBUG
+	struct tun_struct *tun = netdev_priv(dev);
+	return tun->debug;
+#else
+	return -EOPNOTSUPP;
+#endif
+}
+
+static void tun_set_msglevel(struct net_device *dev, u32 value)
+{
+#ifdef TUN_DEBUG
+	struct tun_struct *tun = netdev_priv(dev);
+	tun->debug = value;
+#endif
+}
+
+static u32 tun_get_link(struct net_device *dev)
+{
+	struct tun_struct *tun = netdev_priv(dev);
+	return tun->attached;
+}
+
+static u32 tun_get_rx_csum(struct net_device *dev)
+{
+	struct tun_struct *tun = netdev_priv(dev);
+	return (tun->flags & TUN_NOCHECKSUM) == 0;
+}
+
+static int tun_set_rx_csum(struct net_device *dev, u32 data)
+{
+	struct tun_struct *tun = netdev_priv(dev);
+	if (data)
+		tun->flags &= ~TUN_NOCHECKSUM;
+	else
+		tun->flags |= TUN_NOCHECKSUM;
+	return 0;
+}
+
+static struct ethtool_ops tun_ethtool_ops = {
+	.get_settings	= tun_get_settings,
+	.get_drvinfo	= tun_get_drvinfo,
+	.get_msglevel	= tun_get_msglevel,
+	.set_msglevel	= tun_set_msglevel,
+	.get_link	= tun_get_link,
+	.get_rx_csum	= tun_get_rx_csum,
+	.set_rx_csum	= tun_set_rx_csum
+};
+
 int __init tun_init(void)
 {
 	int ret = 0;
 
-	printk(KERN_INFO "Universal TUN/TAP device driver %s " 
-	       "(C)1999-2002 Maxim Krasnyansky\n", TUN_VER);
+	printk(KERN_INFO "tun: %s, %s\n", DRV_DESCRIPTION, DRV_VERSION);
+	printk(KERN_INFO "tun: %s\n", DRV_COPYRIGHT);
 
 	ret = misc_register(&tun_miscdev);
 	if (ret)
@@ -638,5 +744,7 @@ void tun_cleanup(void)
 
 module_init(tun_init);
 module_exit(tun_cleanup);
+MODULE_DESCRIPTION(DRV_DESCRIPTION);
+MODULE_AUTHOR(DRV_COPYRIGHT);
 MODULE_LICENSE("GPL");
 MODULE_ALIAS_MISCDEV(TUN_MINOR);

include/linux/if_tun.h

@@ -53,7 +53,7 @@ struct tun_struct {
 #endif /* __KERNEL__ */
 
 /* Read queue size */
-#define TUN_READQ_SIZE	10
+#define TUN_READQ_SIZE	500
 
 /* TUN device flags */
 #define TUN_TUN_DEV 	0x0001