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>

1 files changed, 581 insertions, 0 deletions

diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
new file mode 100644
index 000000000000..ad1f6ef89308
--- /dev/null
+++ b/drivers/net/macvtap.c
@@ -0,0 +1,581 @@
+#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");