tun: export underlying socket

Tun device looks similar to a packet socket
in that both pass complete frames from/to userspace.

This patch fills in enough fields in the socket underlying tun driver
to support sendmsg/recvmsg operations, and message flags
MSG_TRUNC and MSG_DONTWAIT, and exports access to this socket
to modules.  Regular read/write behaviour is unchanged.

This way, code using raw sockets to inject packets
into a physical device, can support injecting
packets into host network stack almost without modification.

First user of this interface will be vhost virtualization
accelerator.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Herbert Xu <herbert@gondor.apana.org.au>
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 82 insertions, 19 deletions

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 2834a01bae24..5adb3d150552 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -144,6 +144,7 @@ static int tun_attach(struct tun_struct *tun, struct file *file)
         err = 0;
         tfile->tun = tun;
         tun->tfile = tfile;
+        tun->socket.file = file;
         dev_hold(tun->dev);
         sock_hold(tun->socket.sk);
         atomic_inc(&tfile->count);
@@ -158,6 +159,7 @@ static void __tun_detach(struct tun_struct *tun)
         /* Detach from net device */
         netif_tx_lock_bh(tun->dev);
         tun->tfile = NULL;
+        tun->socket.file = NULL;
         netif_tx_unlock_bh(tun->dev);
 
         /* Drop read queue */
@@ -387,7 +389,8 @@ static netdev_tx_t tun_net_xmit(struct sk_buff *skb, struct net_device *dev)
         /* Notify and wake up reader process */
         if (tun->flags & TUN_FASYNC)
                 kill_fasync(&tun->fasync, SIGIO, POLL_IN);
-        wake_up_interruptible(&tun->socket.wait);
+        wake_up_interruptible_poll(&tun->socket.wait, POLLIN |
+                                   POLLRDNORM | POLLRDBAND);
         return NETDEV_TX_OK;
 
 drop:
@@ -743,7 +746,7 @@ static __inline__ ssize_t tun_put_user(struct tun_struct *tun,
         len = min_t(int, skb->len, len);
 
         skb_copy_datagram_const_iovec(skb, 0, iv, total, len);
-        total += len;
+        total += skb->len;
 
         tun->dev->stats.tx_packets++;
         tun->dev->stats.tx_bytes += len;
@@ -751,34 +754,23 @@ static __inline__ ssize_t tun_put_user(struct tun_struct *tun,
         return total;
 }
 
-static ssize_t tun_chr_aio_read(struct kiocb *iocb, const struct iovec *iv,
-                            unsigned long count, loff_t pos)
+static ssize_t tun_do_read(struct tun_struct *tun,
+                           struct kiocb *iocb, const struct iovec *iv,
+                           ssize_t len, int noblock)
 {
-        struct file *file = iocb->ki_filp;
-        struct tun_file *tfile = file->private_data;
-        struct tun_struct *tun = __tun_get(tfile);
         DECLARE_WAITQUEUE(wait, current);
         struct sk_buff *skb;
-        ssize_t len, ret = 0;
-
-        if (!tun)
-                return -EBADFD;
+        ssize_t ret = 0;
 
         DBG(KERN_INFO "%s: tun_chr_read\n", tun->dev->name);
 
-        len = iov_length(iv, count);
-        if (len < 0) {
-                ret = -EINVAL;
-                goto out;
-        }
-
         add_wait_queue(&tun->socket.wait, &wait);
         while (len) {
                 current->state = TASK_INTERRUPTIBLE;
 
                 /* Read frames from the queue */
                 if (!(skb=skb_dequeue(&tun->socket.sk->sk_receive_queue))) {
-                        if (file->f_flags & O_NONBLOCK) {
+                        if (noblock) {
                                 ret = -EAGAIN;
                                 break;
                         }
@@ -805,6 +797,27 @@ static ssize_t tun_chr_aio_read(struct kiocb *iocb, const struct iovec *iv,
         current->state = TASK_RUNNING;
         remove_wait_queue(&tun->socket.wait, &wait);
 
+        return ret;
+}
+
+static ssize_t tun_chr_aio_read(struct kiocb *iocb, const struct iovec *iv,
+                            unsigned long count, loff_t pos)
+{
+        struct file *file = iocb->ki_filp;
+        struct tun_file *tfile = file->private_data;
+        struct tun_struct *tun = __tun_get(tfile);
+        ssize_t len, ret;
+
+        if (!tun)
+                return -EBADFD;
+        len = iov_length(iv, count);
+        if (len < 0) {
+                ret = -EINVAL;
+                goto out;
+        }
+
+        ret = tun_do_read(tun, iocb, iv, len, file->f_flags & O_NONBLOCK);
+        ret = min_t(ssize_t, ret, len);
 out:
         tun_put(tun);
         return ret;
@@ -847,7 +860,8 @@ static void tun_sock_write_space(struct sock *sk)
                 return;
 
         if (sk->sk_sleep && waitqueue_active(sk->sk_sleep))
-                wake_up_interruptible_sync(sk->sk_sleep);
+                wake_up_interruptible_sync_poll(sk->sk_sleep, POLLOUT |
+                                                POLLWRNORM | POLLWRBAND);
 
         tun = tun_sk(sk)->tun;
         kill_fasync(&tun->fasync, SIGIO, POLL_OUT);
@@ -858,6 +872,37 @@ static void tun_sock_destruct(struct sock *sk)
         free_netdev(tun_sk(sk)->tun->dev);
 }
 
+static int tun_sendmsg(struct kiocb *iocb, struct socket *sock,
+                       struct msghdr *m, size_t total_len)
+{
+        struct tun_struct *tun = container_of(sock, struct tun_struct, socket);
+        return tun_get_user(tun, m->msg_iov, total_len,
+                            m->msg_flags & MSG_DONTWAIT);
+}
+
+static int tun_recvmsg(struct kiocb *iocb, struct socket *sock,
+                       struct msghdr *m, size_t total_len,
+                       int flags)
+{
+        struct tun_struct *tun = container_of(sock, struct tun_struct, socket);
+        int ret;
+        if (flags & ~(MSG_DONTWAIT|MSG_TRUNC))
+                return -EINVAL;
+        ret = tun_do_read(tun, iocb, m->msg_iov, total_len,
+                          flags & MSG_DONTWAIT);
+        if (ret > total_len) {
+                m->msg_flags |= MSG_TRUNC;
+                ret = flags & MSG_TRUNC ? ret : total_len;
+        }
+        return ret;
+}
+
+/* Ops structure to mimic raw sockets with tun */
+static const struct proto_ops tun_socket_ops = {
+        .sendmsg = tun_sendmsg,
+        .recvmsg = tun_recvmsg,
+};
+
 static struct proto tun_proto = {
         .name           = "tun",
         .owner          = THIS_MODULE,
@@ -986,6 +1031,7 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
                         goto err_free_dev;
 
                 init_waitqueue_head(&tun->socket.wait);
+                tun->socket.ops = &tun_socket_ops;
                 sock_init_data(&tun->socket, sk);
                 sk->sk_write_space = tun_sock_write_space;
                 sk->sk_sndbuf = INT_MAX;
@@ -1525,6 +1571,23 @@ static void tun_cleanup(void)
         rtnl_link_unregister(&tun_link_ops);
 }
 
+/* Get an underlying socket object from tun file.  Returns error unless file is
+ * attached to a device.  The returned object works like a packet socket, it
+ * can be used for sock_sendmsg/sock_recvmsg.  The caller is responsible for
+ * 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;
+        if (file->f_op != &tun_fops)
+                return ERR_PTR(-EINVAL);
+        tun = tun_get(file);
+        if (!tun)
+                return ERR_PTR(-EBADFD);
+        tun_put(tun);
+        return &tun->socket;
+}
+EXPORT_SYMBOL_GPL(tun_get_socket);
+
 module_init(tun_init);
 module_exit(tun_cleanup);
 MODULE_DESCRIPTION(DRV_DESCRIPTION);