net: macvtap driver

In order to use macvlan with qemu and other tools that require
a tap file descriptor, the macvtap driver adds a small backend
with a character device with the same interface as the tun
driver, with a minimum set of features.

Macvtap interfaces are created in the same way as macvlan
interfaces using ip link, but the netif is just used as a
handle for configuration and accounting, while the data
goes through the chardev. Each macvtap interface has its
own character device, simplifying permission management
significantly over the generic tun/tap driver.

Cc: Patrick McHardy <kaber@trash.net>
Cc: Stephen Hemminger <shemminger@linux-foundation.org>
Cc: David S. Miller" <davem@davemloft.net>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Or Gerlitz <ogerlitz@voltaire.com>
Cc: netdev@vger.kernel.org
Cc: bridge@lists.linux-foundation.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/Kconfig

@@ -90,6 +90,18 @@ config MACVLAN
 	  To compile this driver as a module, choose M here: the module
 	  will be called macvlan.
 
+config MACVTAP
+	tristate "MAC-VLAN based tap driver (EXPERIMENTAL)"
+	depends on MACVLAN
+	help
+	  This adds a specialized tap character device driver that is based
+	  on the MAC-VLAN network interface, called macvtap. A macvtap device
+	  can be added in the same way as a macvlan device, using 'type
+	  macvlan', and then be accessed through the tap user space interface.
+
+	  To compile this driver as a module, choose M here: the module
+	  will be called macvtap.
+
 config EQUALIZER
 	tristate "EQL (serial line load balancing) support"
 	---help---

drivers/net/Makefile

@@ -169,6 +169,7 @@ obj-$(CONFIG_XEN_NETDEV_FRONTEND) += xen-netfront.o
 obj-$(CONFIG_DUMMY) += dummy.o
 obj-$(CONFIG_IFB) += ifb.o
 obj-$(CONFIG_MACVLAN) += macvlan.o
+obj-$(CONFIG_MACVTAP) += macvtap.o
 obj-$(CONFIG_DE600) += de600.o
 obj-$(CONFIG_DE620) += de620.o
 obj-$(CONFIG_LANCE) += lance.o

drivers/net/macvtap.c

+#include <linux/etherdevice.h>
+#include <linux/if_macvlan.h>
+#include <linux/interrupt.h>
+#include <linux/nsproxy.h>
+#include <linux/compat.h>
+#include <linux/if_tun.h>
+#include <linux/module.h>
+#include <linux/skbuff.h>
+#include <linux/cache.h>
+#include <linux/sched.h>
+#include <linux/types.h>
+#include <linux/init.h>
+#include <linux/wait.h>
+#include <linux/cdev.h>
+#include <linux/fs.h>
+
+#include <net/net_namespace.h>
+#include <net/rtnetlink.h>
+#include <net/sock.h>
+
+/*
+ * A macvtap queue is the central object of this driver, it connects
+ * an open character device to a macvlan interface. There can be
+ * multiple queues on one interface, which map back to queues
+ * implemented in hardware on the underlying device.
+ *
+ * macvtap_proto is used to allocate queues through the sock allocation
+ * mechanism.
+ *
+ * TODO: multiqueue support is currently not implemented, even though
+ * macvtap is basically prepared for that. We will need to add this
+ * here as well as in virtio-net and qemu to get line rate on 10gbit
+ * adapters from a guest.
+ */
+struct macvtap_queue {
+	struct sock sk;
+	struct socket sock;
+	struct macvlan_dev *vlan;
+	struct file *file;
+};
+
+static struct proto macvtap_proto = {
+	.name = "macvtap",
+	.owner = THIS_MODULE,
+	.obj_size = sizeof (struct macvtap_queue),
+};
+
+/*
+ * Minor number matches netdev->ifindex, so need a potentially
+ * large value. This also makes it possible to split the
+ * tap functionality out again in the future by offering it
+ * from other drivers besides macvtap. As long as every device
+ * only has one tap, the interface numbers assure that the
+ * device nodes are unique.
+ */
+static unsigned int macvtap_major;
+#define MACVTAP_NUM_DEVS 65536
+static struct class *macvtap_class;
+static struct cdev macvtap_cdev;
+
+/*
+ * RCU usage:
+ * The macvtap_queue is referenced both from the chardev struct file
+ * and from the struct macvlan_dev using rcu_read_lock.
+ *
+ * We never actually update the contents of a macvtap_queue atomically
+ * with RCU but it is used for race-free destruction of a queue when
+ * either the file or the macvlan_dev goes away. Pointers back to
+ * the dev and the file are implicitly valid as long as the queue
+ * exists.
+ *
+ * The callbacks from macvlan are always done with rcu_read_lock held
+ * already, while in the file_operations, we get it ourselves.
+ *
+ * When destroying a queue, we remove the pointers from the file and
+ * from the dev and then synchronize_rcu to make sure no thread is
+ * still using the queue. There may still be references to the struct
+ * sock inside of the queue from outbound SKBs, but these never
+ * reference back to the file or the dev. The data structure is freed
+ * through __sk_free when both our references and any pending SKBs
+ * are gone.
+ *
+ * macvtap_lock is only used to prevent multiple concurrent open()
+ * calls to assign a new vlan->tap pointer. It could be moved into
+ * the macvlan_dev itself but is extremely rarely used.
+ */
+static DEFINE_SPINLOCK(macvtap_lock);
+
+/*
+ * Choose the next free queue, for now there is only one
+ */
+static int macvtap_set_queue(struct net_device *dev, struct file *file,
+				struct macvtap_queue *q)
+{
+	struct macvlan_dev *vlan = netdev_priv(dev);
+	int err = -EBUSY;
+
+	spin_lock(&macvtap_lock);
+	if (rcu_dereference(vlan->tap))
+		goto out;
+
+	err = 0;
+	q->vlan = vlan;
+	rcu_assign_pointer(vlan->tap, q);
+
+	q->file = file;
+	rcu_assign_pointer(file->private_data, q);
+
+out:
+	spin_unlock(&macvtap_lock);
+	return err;
+}
+
+/*
+ * We must destroy each queue exactly once, when either
+ * the netdev or the file go away.
+ *
+ * Using the spinlock makes sure that we don't get
+ * to the queue again after destroying it.
+ *
+ * synchronize_rcu serializes with the packet flow
+ * that uses rcu_read_lock.
+ */
+static void macvtap_del_queue(struct macvtap_queue **qp)
+{
+	struct macvtap_queue *q;
+
+	spin_lock(&macvtap_lock);
+	q = rcu_dereference(*qp);
+	if (!q) {
+		spin_unlock(&macvtap_lock);
+		return;
+	}
+
+	rcu_assign_pointer(q->vlan->tap, NULL);
+	rcu_assign_pointer(q->file->private_data, NULL);
+	spin_unlock(&macvtap_lock);
+
+	synchronize_rcu();
+	sock_put(&q->sk);
+}
+
+/*
+ * Since we only support one queue, just dereference the pointer.
+ */
+static struct macvtap_queue *macvtap_get_queue(struct net_device *dev,
+					       struct sk_buff *skb)
+{
+	struct macvlan_dev *vlan = netdev_priv(dev);
+
+	return rcu_dereference(vlan->tap);
+}
+
+static void macvtap_del_queues(struct net_device *dev)
+{
+	struct macvlan_dev *vlan = netdev_priv(dev);
+	macvtap_del_queue(&vlan->tap);
+}
+
+static inline struct macvtap_queue *macvtap_file_get_queue(struct file *file)
+{
+	rcu_read_lock_bh();
+	return rcu_dereference(file->private_data);
+}
+
+static inline void macvtap_file_put_queue(void)
+{
+	rcu_read_unlock_bh();
+}
+
+/*
+ * Forward happens for data that gets sent from one macvlan
+ * endpoint to another one in bridge mode. We just take
+ * the skb and put it into the receive queue.
+ */
+static int macvtap_forward(struct net_device *dev, struct sk_buff *skb)
+{
+	struct macvtap_queue *q = macvtap_get_queue(dev, skb);
+	if (!q)
+		return -ENOLINK;
+
+	skb_queue_tail(&q->sk.sk_receive_queue, skb);
+	wake_up(q->sk.sk_sleep);
+	return 0;
+}
+
+/*
+ * Receive is for data from the external interface (lowerdev),
+ * in case of macvtap, we can treat that the same way as
+ * forward, which macvlan cannot.
+ */
+static int macvtap_receive(struct sk_buff *skb)
+{
+	skb_push(skb, ETH_HLEN);
+	return macvtap_forward(skb->dev, skb);
+}
+
+static int macvtap_newlink(struct net *src_net,
+			   struct net_device *dev,
+			   struct nlattr *tb[],
+			   struct nlattr *data[])
+{
+	struct device *classdev;
+	dev_t devt;
+	int err;
+
+	err = macvlan_common_newlink(src_net, dev, tb, data,
+				     macvtap_receive, macvtap_forward);
+	if (err)
+		goto out;
+
+	devt = MKDEV(MAJOR(macvtap_major), dev->ifindex);
+
+	classdev = device_create(macvtap_class, &dev->dev, devt,
+				 dev, "tap%d", dev->ifindex);
+	if (IS_ERR(classdev)) {
+		err = PTR_ERR(classdev);
+		macvtap_del_queues(dev);
+	}
+
+out:
+	return err;
+}
+
+static void macvtap_dellink(struct net_device *dev,
+			    struct list_head *head)
+{
+	device_destroy(macvtap_class,
+		       MKDEV(MAJOR(macvtap_major), dev->ifindex));
+
+	macvtap_del_queues(dev);
+	macvlan_dellink(dev, head);
+}
+
+static struct rtnl_link_ops macvtap_link_ops __read_mostly = {
+	.kind		= "macvtap",
+	.newlink	= macvtap_newlink,
+	.dellink	= macvtap_dellink,
+};
+
+
+static void macvtap_sock_write_space(struct sock *sk)
+{
+	if (!sock_writeable(sk) ||
+	    !test_and_clear_bit(SOCK_ASYNC_NOSPACE, &sk->sk_socket->flags))
+		return;
+
+	if (sk->sk_sleep && waitqueue_active(sk->sk_sleep))
+		wake_up_interruptible_sync(sk->sk_sleep);
+}
+
+static int macvtap_open(struct inode *inode, struct file *file)
+{
+	struct net *net = current->nsproxy->net_ns;
+	struct net_device *dev = dev_get_by_index(net, iminor(inode));
+	struct macvtap_queue *q;
+	int err;
+
+	err = -ENODEV;
+	if (!dev)
+		goto out;
+
+	/* check if this is a macvtap device */
+	err = -EINVAL;
+	if (dev->rtnl_link_ops != &macvtap_link_ops)
+		goto out;
+
+	err = -ENOMEM;
+	q = (struct macvtap_queue *)sk_alloc(net, AF_UNSPEC, GFP_KERNEL,
+					     &macvtap_proto);
+	if (!q)
+		goto out;
+
+	init_waitqueue_head(&q->sock.wait);
+	q->sock.type = SOCK_RAW;
+	q->sock.state = SS_CONNECTED;
+	sock_init_data(&q->sock, &q->sk);
+	q->sk.sk_allocation = GFP_ATOMIC; /* for now */
+	q->sk.sk_write_space = macvtap_sock_write_space;
+
+	err = macvtap_set_queue(dev, file, q);
+	if (err)
+		sock_put(&q->sk);
+
+out:
+	if (dev)
+		dev_put(dev);
+
+	return err;
+}
+
+static int macvtap_release(struct inode *inode, struct file *file)
+{
+	macvtap_del_queue((struct macvtap_queue **)&file->private_data);
+	return 0;
+}
+
+static unsigned int macvtap_poll(struct file *file, poll_table * wait)
+{
+	struct macvtap_queue *q = macvtap_file_get_queue(file);
+	unsigned int mask = POLLERR;
+
+	if (!q)
+		goto out;
+
+	mask = 0;
+	poll_wait(file, &q->sock.wait, wait);
+
+	if (!skb_queue_empty(&q->sk.sk_receive_queue))
+		mask |= POLLIN | POLLRDNORM;
+
+	if (sock_writeable(&q->sk) ||
+	    (!test_and_set_bit(SOCK_ASYNC_NOSPACE, &q->sock.flags) &&
+	     sock_writeable(&q->sk)))
+		mask |= POLLOUT | POLLWRNORM;
+
+out:
+	macvtap_file_put_queue();
+	return mask;
+}
+
+/* Get packet from user space buffer */
+static ssize_t macvtap_get_user(struct macvtap_queue *q,
+				const struct iovec *iv, size_t count,
+				int noblock)
+{
+	struct sk_buff *skb;
+	size_t len = count;
+	int err;
+
+	if (unlikely(len < ETH_HLEN))
+		return -EINVAL;
+
+	skb = sock_alloc_send_skb(&q->sk, NET_IP_ALIGN + len, noblock, &err);
+
+	if (!skb) {
+		macvlan_count_rx(q->vlan, 0, false, false);
+		return err;
+	}
+
+	skb_reserve(skb, NET_IP_ALIGN);
+	skb_put(skb, count);
+
+	if (skb_copy_datagram_from_iovec(skb, 0, iv, 0, len)) {
+		macvlan_count_rx(q->vlan, 0, false, false);
+		kfree_skb(skb);
+		return -EFAULT;
+	}
+
+	skb_set_network_header(skb, ETH_HLEN);
+
+	macvlan_start_xmit(skb, q->vlan->dev);
+
+	return count;
+}
+
+static ssize_t macvtap_aio_write(struct kiocb *iocb, const struct iovec *iv,
+				 unsigned long count, loff_t pos)
+{
+	struct file *file = iocb->ki_filp;
+	ssize_t result = -ENOLINK;
+	struct macvtap_queue *q = macvtap_file_get_queue(file);
+
+	if (!q)
+		goto out;
+
+	result = macvtap_get_user(q, iv, iov_length(iv, count),
+			      file->f_flags & O_NONBLOCK);
+out:
+	macvtap_file_put_queue();
+	return result;
+}
+
+/* Put packet to the user space buffer */
+static ssize_t macvtap_put_user(struct macvtap_queue *q,
+				const struct sk_buff *skb,
+				const struct iovec *iv, int len)
+{
+	struct macvlan_dev *vlan = q->vlan;
+	int ret;
+
+	len = min_t(int, skb->len, len);
+
+	ret = skb_copy_datagram_const_iovec(skb, 0, iv, 0, len);
+
+	macvlan_count_rx(vlan, len, ret == 0, 0);
+
+	return ret ? ret : len;
+}
+
+static ssize_t macvtap_aio_read(struct kiocb *iocb, const struct iovec *iv,
+				unsigned long count, loff_t pos)
+{
+	struct file *file = iocb->ki_filp;
+	struct macvtap_queue *q = macvtap_file_get_queue(file);
+
+	DECLARE_WAITQUEUE(wait, current);
+	struct sk_buff *skb;
+	ssize_t len, ret = 0;
+
+	if (!q) {
+		ret = -ENOLINK;
+		goto out;
+	}
+
+	len = iov_length(iv, count);
+	if (len < 0) {
+		ret = -EINVAL;
+		goto out;
+	}
+
+	add_wait_queue(q->sk.sk_sleep, &wait);
+	while (len) {
+		current->state = TASK_INTERRUPTIBLE;
+
+		/* Read frames from the queue */
+		skb = skb_dequeue(&q->sk.sk_receive_queue);
+		if (!skb) {
+			if (file->f_flags & O_NONBLOCK) {
+				ret = -EAGAIN;
+				break;
+			}
+			if (signal_pending(current)) {
+				ret = -ERESTARTSYS;
+				break;
+			}
+			/* Nothing to read, let's sleep */
+			schedule();
+			continue;
+		}
+		ret = macvtap_put_user(q, skb, iv, len);
+		kfree_skb(skb);
+		break;
+	}
+
+	current->state = TASK_RUNNING;
+	remove_wait_queue(q->sk.sk_sleep, &wait);
+
+out:
+	macvtap_file_put_queue();
+	return ret;
+}
+
+/*
+ * provide compatibility with generic tun/tap interface
+ */
+static long macvtap_ioctl(struct file *file, unsigned int cmd,
+			  unsigned long arg)
+{
+	struct macvtap_queue *q;
+	void __user *argp = (void __user *)arg;
+	struct ifreq __user *ifr = argp;
+	unsigned int __user *up = argp;
+	unsigned int u;
+	char devname[IFNAMSIZ];
+
+	switch (cmd) {
+	case TUNSETIFF:
+		/* ignore the name, just look at flags */
+		if (get_user(u, &ifr->ifr_flags))
+			return -EFAULT;
+		if (u != (IFF_TAP | IFF_NO_PI))
+			return -EINVAL;
+		return 0;
+
+	case TUNGETIFF:
+		q = macvtap_file_get_queue(file);
+		if (!q)
+			return -ENOLINK;
+		memcpy(devname, q->vlan->dev->name, sizeof(devname));
+		macvtap_file_put_queue();
+
+		if (copy_to_user(&ifr->ifr_name, q->vlan->dev->name, IFNAMSIZ) ||
+		    put_user((TUN_TAP_DEV | TUN_NO_PI), &ifr->ifr_flags))
+			return -EFAULT;
+		return 0;
+
+	case TUNGETFEATURES:
+		if (put_user((IFF_TAP | IFF_NO_PI), up))
+			return -EFAULT;
+		return 0;
+
+	case TUNSETSNDBUF:
+		if (get_user(u, up))
+			return -EFAULT;
+
+		q = macvtap_file_get_queue(file);
+		q->sk.sk_sndbuf = u;
+		macvtap_file_put_queue();
+		return 0;
+
+	case TUNSETOFFLOAD:
+		/* let the user check for future flags */
+		if (arg & ~(TUN_F_CSUM | TUN_F_TSO4 | TUN_F_TSO6 |
+			  TUN_F_TSO_ECN | TUN_F_UFO))
+			return -EINVAL;
+
+		/* TODO: add support for these, so far we don't
+			 support any offload */
+		if (arg & (TUN_F_CSUM | TUN_F_TSO4 | TUN_F_TSO6 |
+			 TUN_F_TSO_ECN | TUN_F_UFO))
+			return -EINVAL;
+
+		return 0;
+
+	default:
+		return -EINVAL;
+	}
+}
+
+#ifdef CONFIG_COMPAT
+static long macvtap_compat_ioctl(struct file *file, unsigned int cmd,
+				 unsigned long arg)
+{
+	return macvtap_ioctl(file, cmd, (unsigned long)compat_ptr(arg));
+}
+#endif
+
+static const struct file_operations macvtap_fops = {
+	.owner		= THIS_MODULE,
+	.open		= macvtap_open,
+	.release	= macvtap_release,
+	.aio_read	= macvtap_aio_read,
+	.aio_write	= macvtap_aio_write,
+	.poll		= macvtap_poll,
+	.llseek		= no_llseek,
+	.unlocked_ioctl	= macvtap_ioctl,
+#ifdef CONFIG_COMPAT
+	.compat_ioctl	= macvtap_compat_ioctl,
+#endif
+};
+
+static int macvtap_init(void)
+{
+	int err;
+
+	err = alloc_chrdev_region(&macvtap_major, 0,
+				MACVTAP_NUM_DEVS, "macvtap");
+	if (err)
+		goto out1;
+
+	cdev_init(&macvtap_cdev, &macvtap_fops);
+	err = cdev_add(&macvtap_cdev, macvtap_major, MACVTAP_NUM_DEVS);
+	if (err)
+		goto out2;
+
+	macvtap_class = class_create(THIS_MODULE, "macvtap");
+	if (IS_ERR(macvtap_class)) {
+		err = PTR_ERR(macvtap_class);
+		goto out3;
+	}
+
+	err = macvlan_link_register(&macvtap_link_ops);
+	if (err)
+		goto out4;
+
+	return 0;
+
+out4:
+	class_unregister(macvtap_class);
+out3:
+	cdev_del(&macvtap_cdev);
+out2:
+	unregister_chrdev_region(macvtap_major, MACVTAP_NUM_DEVS);
+out1:
+	return err;
+}
+module_init(macvtap_init);
+
+static void macvtap_exit(void)
+{
+	rtnl_link_unregister(&macvtap_link_ops);
+	class_unregister(macvtap_class);
+	cdev_del(&macvtap_cdev);
+	unregister_chrdev_region(macvtap_major, MACVTAP_NUM_DEVS);
+}
+module_exit(macvtap_exit);
+
+MODULE_ALIAS_RTNL_LINK("macvtap");
+MODULE_AUTHOR("Arnd Bergmann <arnd@arndb.de>");
+MODULE_LICENSE("GPL");

include/linux/if_macvlan.h

@@ -34,6 +34,7 @@ struct macvlan_dev {
 	enum macvlan_mode	mode;
 	int (*receive)(struct sk_buff *skb);
 	int (*forward)(struct net_device *dev, struct sk_buff *skb);
+	struct macvtap_queue	*tap;
 };
 
 static inline void macvlan_count_rx(const struct macvlan_dev *vlan,