Date:	Fri, 12 Aug 2011 09:55:20 +0800
From:	Jason Wang <jasowang@...hat.com>
To:	mst@...hat.com, netdev@...r.kernel.org, jasowang@...hat.com,
	linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org, davem@...emloft.net
Cc:	krkumar2@...ibm.com, rusty@...tcorp.com.au, qemu-devel@...gnu.org,
	kvm@...r.kernel.org, mirq-linux@...e.qmqm.pl
Subject: [net-next RFC PATCH 4/7] tuntap: multiqueue support

With the abstraction that each socket were a backend of a
queue for userspace, this patch adds multiqueue support for
tap device by allowing multiple sockets to be attached to a
tap device. Then we could parallize the transmission by put
them into different socket.

As queue related information were stored in private_data of
file new, we could simply implement the multiqueue support
by add an array of pointers to sockets were stored in the
tap device. Then ioctls may be added to manipulate those
pointers for adding or removing queues.

In order to let tx path lockless, NETIF_F_LLTX were used for
multiqueue tap device. And RCU is used for doing
synchronization between packet handling and system calls
such as removing queues.

Currently, multiqueue support is limited for tap , but it's
easy also enable it for tun if we find it was also helpful.

Signed-off-by: Jason Wang <jasowang@...hat.com>
---
 drivers/net/tun.c |  376 ++++++++++++++++++++++++++++++++++-------------------
 1 files changed, 243 insertions(+), 133 deletions(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 4cd292a..8bc6dff 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -108,6 +108,8 @@ struct tap_filter {
 	unsigned char	addr[FLT_EXACT_COUNT][ETH_ALEN];
 };
 
+#define MAX_TAP_QUEUES (NR_CPUS < 16 ? NR_CPUS : 16)
+
 struct tun_file {
 	struct sock sk;
 	struct socket socket;
@@ -115,7 +117,7 @@ struct tun_file {
 	int vnet_hdr_sz;
 	struct tap_filter txflt;
 	atomic_t count;
-	struct tun_struct *tun;
+	struct tun_struct __rcu *tun;
 	struct net *net;
 	struct fasync_struct *fasync;
 	unsigned int flags;
@@ -124,7 +126,8 @@ struct tun_file {
 struct tun_sock;
 
 struct tun_struct {
-	struct tun_file		*tfile;
+	struct tun_file		*tfiles[MAX_TAP_QUEUES];
+	unsigned int            numqueues;
 	unsigned int 		flags;
 	uid_t			owner;
 	gid_t			group;
@@ -139,80 +142,183 @@ struct tun_struct {
 #endif
 };
 
-static int tun_attach(struct tun_struct *tun, struct file *file)
+static DEFINE_SPINLOCK(tun_lock);
+
+/*
+ * get_slot: return a [unused/occupied] slot in tun->tfiles[]:
+ *     - if 'f' is NULL, return the first empty slot;
+ *     - otherwise, return the slot this pointer occupies.
+ */
+static int tun_get_slot(struct tun_struct *tun, struct tun_file *tfile)
 {
-	struct tun_file *tfile = file->private_data;
-	int err;
+	int i;
 
-	ASSERT_RTNL();
+	for (i = 0; i < MAX_TAP_QUEUES; i++) {
+		if (rcu_dereference(tun->tfiles[i]) == tfile)
+			return i;
+	}
 
-	netif_tx_lock_bh(tun->dev);
+       /* Should never happen */
+       BUG_ON(1);
+}
 
-	err = -EINVAL;
-	if (tfile->tun)
-		goto out;
+/*
+ * tun_get_queue(): calculate the queue index
+ *     - if skbs comes from mq nics, we can just borrow
+ *     - if not, calculate from the hash
+ */
+static struct tun_file *tun_get_queue(struct net_device *dev,
+                                     struct sk_buff *skb)
+{
+	struct tun_struct *tun = netdev_priv(dev);
+	struct tun_file *tfile = NULL;
+	int numqueues = tun->numqueues;
+	__u32 rxq;
 
-	err = -EBUSY;
-	if (tun->tfile)
+	BUG_ON(!rcu_read_lock_held());
+
+	if (!numqueues)
 		goto out;
 
-	err = 0;
-	tfile->tun = tun;
-	tun->tfile = tfile;
-	netif_carrier_on(tun->dev);
-	dev_hold(tun->dev);
-	sock_hold(&tfile->sk);
-	atomic_inc(&tfile->count);
+	if (likely(skb_rx_queue_recorded(skb))) {
+		rxq = skb_get_rx_queue(skb);
+
+		while (unlikely(rxq >= numqueues))
+			rxq -= numqueues;
+
+		tfile = rcu_dereference(tun->tfiles[rxq]);
+		if (tfile)
+			goto out;
+	}
+
+	/* Check if we can use flow to select a queue */
+	rxq = skb_get_rxhash(skb);
+	if (rxq) {
+		tfile = rcu_dereference(tun->tfiles[rxq % numqueues]);
+		if (tfile)
+			goto out;
+	}
+
+	/* Everything failed - find first available queue */
+	for (rxq = 0; rxq < MAX_TAP_QUEUES; rxq++) {
+		tfile = rcu_dereference(tun->tfiles[rxq]);
+		if (tfile)
+			break;
+	}
 
 out:
-	netif_tx_unlock_bh(tun->dev);
-	return err;
+	return tfile;
 }
 
-static void __tun_detach(struct tun_struct *tun)
+static int tun_detach(struct tun_file *tfile, bool clean)
 {
-	struct tun_file *tfile = tun->tfile;
-	/* Detach from net device */
-	netif_tx_lock_bh(tun->dev);
-	netif_carrier_off(tun->dev);
-	tun->tfile = NULL;
-	netif_tx_unlock_bh(tun->dev);
-
-	/* Drop read queue */
-	skb_queue_purge(&tfile->socket.sk->sk_receive_queue);
-
-	/* Drop the extra count on the net device */
-	dev_put(tun->dev);
-}
+	struct tun_struct *tun;
+	struct net_device *dev = NULL;
+	bool destroy = false;
 
-static void tun_detach(struct tun_struct *tun)
-{
-	rtnl_lock();
-	__tun_detach(tun);
-	rtnl_unlock();
-}
+	spin_lock(&tun_lock);
 
-static struct tun_struct *__tun_get(struct tun_file *tfile)
-{
-	struct tun_struct *tun = NULL;
+	tun = rcu_dereference_protected(tfile->tun,
+					lockdep_is_held(&tun_lock));
+	if (tun) {
+		int index = tun_get_slot(tun, tfile);
+		if (index == -1) {
+			spin_unlock(&tun_lock);
+			return -EINVAL;
+		}
+		dev = tun->dev;
+
+		rcu_assign_pointer(tun->tfiles[index], NULL);
+		rcu_assign_pointer(tfile->tun, NULL);
+		--tun->numqueues;
+		sock_put(&tfile->sk);
 
-	if (atomic_inc_not_zero(&tfile->count))
-		tun = tfile->tun;
+		if (tun->numqueues == 0 && !(tun->flags & TUN_PERSIST))
+			destroy = true;
+	}
+
+	spin_unlock(&tun_lock);
+
+	synchronize_rcu();
+	if (clean)
+		sock_put(&tfile->sk);
 
-	return tun;
+	if (destroy) {
+		rtnl_lock();
+		if (dev->reg_state == NETREG_REGISTERED)
+			unregister_netdevice(dev);
+		rtnl_unlock();
+	}
+
+	return 0;
 }
 
-static struct tun_struct *tun_get(struct file *file)
+static void tun_detach_all(struct net_device *dev)
 {
-	return __tun_get(file->private_data);
+	struct tun_struct *tun = netdev_priv(dev);
+	struct tun_file *tfile, *tfile_list[MAX_TAP_QUEUES];
+	int i, j = 0;
+
+	spin_lock(&tun_lock);
+
+	for (i = 0; i < MAX_TAP_QUEUES && tun->numqueues; i++) {
+		tfile = rcu_dereference_protected(tun->tfiles[i],
+						lockdep_is_held(&tun_lock));
+		if (tfile) {
+			wake_up_all(&tfile->wq.wait);
+			tfile_list[i++] = tfile;
+			rcu_assign_pointer(tun->tfiles[i], NULL);
+			rcu_assign_pointer(tfile->tun, NULL);
+			--tun->numqueues;
+		}
+	}
+	BUG_ON(tun->numqueues != 0);
+	spin_unlock(&tun_lock);
+
+	synchronize_rcu();
+	for(--j; j >= 0; j--)
+		sock_put(&tfile_list[j]->sk);
 }
 
-static void tun_put(struct tun_struct *tun)
+static int tun_attach(struct tun_struct *tun, struct file *file)
 {
-	struct tun_file *tfile = tun->tfile;
+	struct tun_file *tfile = file->private_data;
+	int err, index;
+
+	ASSERT_RTNL();
+
+	spin_lock(&tun_lock);
 
-	if (atomic_dec_and_test(&tfile->count))
-		tun_detach(tfile->tun);
+	err = -EINVAL;
+	if (rcu_dereference_protected(tfile->tun, lockdep_is_held(&tun_lock)))
+		goto out;
+
+	err = -EBUSY;
+	if (!(tun->flags & TUN_TAP_MQ) &&
+		rcu_dereference_protected(tun->tfiles[0],
+					lockdep_is_held(&tun_lock))) {
+		/* Multiqueue is only for TAP */
+		goto out;
+	}
+
+	if (tun->numqueues == MAX_TAP_QUEUES)
+		goto out;
+
+	err = 0;
+	index = tun_get_slot(tun, NULL);
+	BUG_ON(index == -1);
+	rcu_assign_pointer(tfile->tun, tun);
+	rcu_assign_pointer(tun->tfiles[index], tfile);
+	sock_hold(&tfile->sk);
+	tun->numqueues++;
+
+	if (tun->numqueues == 1)
+		netif_carrier_on(tun->dev);
+
+	/* device is allowed to go away first, so no need to hold extra refcnt.	 */
+out:
+	spin_unlock(&tun_lock);
+	return err;
 }
 
 /* TAP filtering */
@@ -332,16 +438,7 @@ static const struct ethtool_ops tun_ethtool_ops;
 /* Net device detach from fd. */
 static void tun_net_uninit(struct net_device *dev)
 {
-	struct tun_struct *tun = netdev_priv(dev);
-	struct tun_file *tfile = tun->tfile;
-
-	/* Inform the methods they need to stop using the dev.
-	 */
-	if (tfile) {
-		wake_up_all(&tfile->wq.wait);
-		if (atomic_dec_and_test(&tfile->count))
-			__tun_detach(tun);
-	}
+	tun_detach_all(dev);
 }
 
 /* Net device open. */
@@ -361,10 +458,10 @@ static int tun_net_close(struct net_device *dev)
 /* Net device start xmit */
 static netdev_tx_t tun_net_xmit(struct sk_buff *skb, struct net_device *dev)
 {
-	struct tun_struct *tun = netdev_priv(dev);
-	struct tun_file *tfile = tun->tfile;
+	struct tun_file *tfile = NULL;
 
-	tun_debug(KERN_INFO, tun, "tun_net_xmit %d\n", skb->len);
+	rcu_read_lock();
+	tfile = tun_get_queue(dev, skb);
 
 	/* Drop packet if interface is not attached */
 	if (!tfile)
@@ -381,7 +478,7 @@ static netdev_tx_t tun_net_xmit(struct sk_buff *skb, struct net_device *dev)
 		goto drop;
 
 	if (skb_queue_len(&tfile->socket.sk->sk_receive_queue) >= dev->tx_queue_len) {
-		if (!(tun->flags & TUN_ONE_QUEUE)) {
+		if (!(tfile->flags & TUN_ONE_QUEUE) && !(tfile->flags && TUN_TAP_MQ)) {
 			/* Normal queueing mode. */
 			/* Packet scheduler handles dropping of further packets. */
 			netif_stop_queue(dev);
@@ -390,7 +487,7 @@ static netdev_tx_t tun_net_xmit(struct sk_buff *skb, struct net_device *dev)
 			 * error is more appropriate. */
 			dev->stats.tx_fifo_errors++;
 		} else {
-			/* Single queue mode.
+			/* Single queue mode or multi queue mode.
 			 * Driver handles dropping of all packets itself. */
 			goto drop;
 		}
@@ -408,9 +505,11 @@ static netdev_tx_t tun_net_xmit(struct sk_buff *skb, struct net_device *dev)
 		kill_fasync(&tfile->fasync, SIGIO, POLL_IN);
 	wake_up_interruptible_poll(&tfile->wq.wait, POLLIN |
 				   POLLRDNORM | POLLRDBAND);
+	rcu_read_unlock();
 	return NETDEV_TX_OK;
 
 drop:
+	rcu_read_unlock();
 	dev->stats.tx_dropped++;
 	kfree_skb(skb);
 	return NETDEV_TX_OK;
@@ -526,16 +625,22 @@ static void tun_net_init(struct net_device *dev)
 static unsigned int tun_chr_poll(struct file *file, poll_table * wait)
 {
 	struct tun_file *tfile = file->private_data;
-	struct tun_struct *tun = __tun_get(tfile);
+	struct tun_struct *tun = NULL;
 	struct sock *sk;
 	unsigned int mask = 0;
 
-	if (!tun)
+	if (!tfile)
 		return POLLERR;
 
-	sk = tfile->socket.sk;
+	rcu_read_lock();
+	tun = rcu_dereference(tfile->tun);
+	if (!tun) {
+		rcu_read_unlock();
+		return POLLERR;
+	}
+	rcu_read_unlock();
 
-	tun_debug(KERN_INFO, tun, "tun_chr_poll\n");
+	sk = &tfile->sk;
 
 	poll_wait(file, &tfile->wq.wait, wait);
 
@@ -547,10 +652,12 @@ static unsigned int tun_chr_poll(struct file *file, poll_table * wait)
 	     sock_writeable(sk)))
 		mask |= POLLOUT | POLLWRNORM;
 
-	if (tun->dev->reg_state != NETREG_REGISTERED)
+	rcu_read_lock();
+	tun = rcu_dereference(tfile->tun);
+	if (!tun || tun->dev->reg_state != NETREG_REGISTERED)
 		mask = POLLERR;
+	rcu_read_unlock();
 
-	tun_put(tun);
 	return mask;
 }
 
@@ -706,8 +813,10 @@ static ssize_t tun_get_user(struct tun_file *tfile,
 		skb_shinfo(skb)->gso_segs = 0;
 	}
 
-	tun = __tun_get(tfile);
+	rcu_read_lock();
+	tun = rcu_dereference(tfile->tun);
 	if (!tun) {
+		rcu_read_unlock();
 		return -EBADFD;
 	}
 
@@ -722,7 +831,7 @@ static ssize_t tun_get_user(struct tun_file *tfile,
 
 	tun->dev->stats.rx_packets++;
 	tun->dev->stats.rx_bytes += len;
-	tun_put(tun);
+	rcu_read_unlock();
 
 	netif_rx_ni(skb);
 
@@ -732,16 +841,17 @@ err_free:
 	count = -EINVAL;
 	kfree_skb(skb);
 err:
-	tun = __tun_get(tfile);
+	rcu_read_lock();
+	tun = rcu_dereference(tfile->tun);
 	if (!tun) {
+		rcu_read_unlock();
 		return -EBADFD;
 	}
-
 	if (drop)
 		tun->dev->stats.rx_dropped++;
 	if (error)
 		tun->dev->stats.rx_frame_errors++;
-	tun_put(tun);
+	rcu_read_unlock();
 	return count;
 }
 
@@ -834,12 +944,13 @@ static ssize_t tun_put_user(struct tun_file *tfile,
 	skb_copy_datagram_const_iovec(skb, 0, iv, total, len);
 	total += skb->len;
 
-	tun = __tun_get(tfile);
+	rcu_read_lock();
+	tun = rcu_dereference(tfile->tun);
 	if (tun) {
 		tun->dev->stats.tx_packets++;
 		tun->dev->stats.tx_bytes += len;
-		tun_put(tun);
 	}
+	rcu_read_unlock();
 
 	return total;
 }
@@ -869,28 +980,31 @@ static ssize_t tun_do_read(struct tun_file *tfile,
 				break;
 			}
 
-			tun = __tun_get(tfile);
+			rcu_read_lock();
+			tun = rcu_dereference(tfile->tun);
 			if (!tun) {
-				ret = -EIO;
+				ret = -EBADFD;
+				rcu_read_unlock();
 				break;
 			}
 			if (tun->dev->reg_state != NETREG_REGISTERED) {
 				ret = -EIO;
-				tun_put(tun);
+				rcu_read_unlock();
 				break;
 			}
-			tun_put(tun);
+			rcu_read_unlock();
 
 			/* Nothing to read, let's sleep */
 			schedule();
 			continue;
 		}
 
-		tun = __tun_get(tfile);
+		rcu_read_lock();
+		tun = rcu_dereference(tfile->tun);
 		if (tun) {
 			netif_wake_queue(tun->dev);
-			tun_put(tun);
 		}
+		rcu_read_unlock();
 
 		ret = tun_put_user(tfile, skb, iv, len);
 		kfree_skb(skb);
@@ -1030,6 +1144,9 @@ static int tun_flags(struct tun_struct *tun)
 	if (tun->flags & TUN_VNET_HDR)
 		flags |= IFF_VNET_HDR;
 
+	if (tun->flags & TUN_TAP_MQ)
+		flags |= IFF_MULTI_QUEUE;
+
 	return flags;
 }
 
@@ -1109,6 +1226,10 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
 			/* TAP device */
 			flags |= TUN_TAP_DEV;
 			name = "tap%d";
+			if (ifr->ifr_flags & IFF_MULTI_QUEUE) {
+				flags |= TUN_TAP_MQ;
+				name = "mqtap%d";
+			}
 		} else
 			return -EINVAL;
 
@@ -1134,6 +1255,8 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
 		dev->hw_features = NETIF_F_SG | NETIF_F_FRAGLIST |
 			TUN_USER_FEATURES;
 		dev->features = dev->hw_features;
+		if (ifr->ifr_flags & IFF_MULTI_QUEUE)
+			dev->features |= NETIF_F_LLTX;
 
 		err = register_netdevice(tun->dev);
 		if (err < 0)
@@ -1166,6 +1289,11 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
 	else
 		tun->flags &= ~TUN_VNET_HDR;
 
+	if (ifr->ifr_flags & IFF_MULTI_QUEUE)
+		tun->flags |= TUN_TAP_MQ;
+	else
+		tun->flags &= ~TUN_TAP_MQ;
+
 	/* Cache flags from tun device */
 	tfile->flags = tun->flags;
 	/* Make sure persistent devices do not get stuck in
@@ -1256,38 +1384,39 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
 				(unsigned int __user*)argp);
 	}
 
-	rtnl_lock();
-
-	tun = __tun_get(tfile);
-	if (cmd == TUNSETIFF && !tun) {
+	ret = 0;
+	if (cmd == TUNSETIFF) {
+		rtnl_lock();
 		ifr.ifr_name[IFNAMSIZ-1] = '\0';
-
 		ret = tun_set_iff(tfile->net, file, &ifr);
-
+		rtnl_unlock();
 		if (ret)
-			goto unlock;
-
+			return ret;
 		if (copy_to_user(argp, &ifr, ifreq_len))
-			ret = -EFAULT;
-		goto unlock;
+			return -EFAULT;
+		return ret;
 	}
 
+	rtnl_lock();
+
+	rcu_read_lock();
+
 	ret = -EBADFD;
+	tun = rcu_dereference(tfile->tun);
 	if (!tun)
 		goto unlock;
 
-	tun_debug(KERN_INFO, tun, "tun_chr_ioctl cmd %d\n", cmd);
 
-	ret = 0;
-	switch (cmd) {
+	switch(cmd) {
 	case TUNGETIFF:
 		ret = tun_get_iff(current->nsproxy->net_ns, tun, &ifr);
+		rcu_read_unlock();
 		if (ret)
-			break;
+			goto out;
 
 		if (copy_to_user(argp, &ifr, ifreq_len))
 			ret = -EFAULT;
-		break;
+		goto out;
 
 	case TUNSETNOCSUM:
 		/* Disable/Enable checksum */
@@ -1349,9 +1478,10 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
 		/* Get hw address */
 		memcpy(ifr.ifr_hwaddr.sa_data, tun->dev->dev_addr, ETH_ALEN);
 		ifr.ifr_hwaddr.sa_family = tun->dev->type;
+		rcu_read_unlock();
 		if (copy_to_user(argp, &ifr, ifreq_len))
 			ret = -EFAULT;
-		break;
+		goto out;
 
 	case SIOCSIFHWADDR:
 		/* Set hw address */
@@ -1367,9 +1497,9 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
 	}
 
 unlock:
+	rcu_read_unlock();
+out:
 	rtnl_unlock();
-	if (tun)
-		tun_put(tun);
 	return ret;
 }
 
@@ -1541,31 +1671,8 @@ static int tun_chr_open(struct inode *inode, struct file * file)
 static int tun_chr_close(struct inode *inode, struct file *file)
 {
 	struct tun_file *tfile = file->private_data;
-	struct tun_struct *tun;
-
-	tun = __tun_get(tfile);
-	if (tun) {
-		struct net_device *dev = tun->dev;
-
-		tun_debug(KERN_INFO, tun, "tun_chr_close\n");
-
-		__tun_detach(tun);
-
-		/* If desirable, unregister the netdevice. */
-		if (!(tun->flags & TUN_PERSIST)) {
-			rtnl_lock();
-			if (dev->reg_state == NETREG_REGISTERED)
-				unregister_netdevice(dev);
-			rtnl_unlock();
-		}
-
-		/* drop the reference that netdevice holds */
-		sock_put(&tfile->sk);
-
-	}
 
-	/* drop the reference that file holds */
-	sock_put(&tfile->sk);
+	tun_detach(tfile, true);
 
 	return 0;
 }
@@ -1693,14 +1800,17 @@ static void tun_cleanup(void)
  * holding a reference to the file for as long as the socket is in use. */
 struct socket *tun_get_socket(struct file *file)
 {
-	struct tun_struct *tun;
+	struct tun_struct *tun = NULL;
 	struct tun_file *tfile = file->private_data;
 	if (file->f_op != &tun_fops)
 		return ERR_PTR(-EINVAL);
-	tun = tun_get(file);
-	if (!tun)
+	rcu_read_lock();
+	tun = rcu_dereference(tfile->tun);
+	if (!tun) {
+		rcu_read_unlock();
 		return ERR_PTR(-EBADFD);
-	tun_put(tun);
+	}
+	rcu_read_unlock();
 	return &tfile->socket;
 }
 EXPORT_SYMBOL_GPL(tun_get_socket);

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