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>

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 2834a01..5adb3d1 100644 (file)
--- 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);

diff --git a/include/linux/if_tun.h b/include/linux/if_tun.h
index 3f5fd52..404abe0 100644 (file)
--- a/include/linux/if_tun.h
+++ b/include/linux/if_tun.h
@@ -86,4 +86,18 @@ struct tun_filter {
        __u8   addr[0][ETH_ALEN];
 };
 
+#ifdef __KERNEL__
+#if defined(CONFIG_TUN) || defined(CONFIG_TUN_MODULE)
+struct socket *tun_get_socket(struct file *);
+#else
+#include <linux/err.h>
+#include <linux/errno.h>
+struct file;
+struct socket;
+static inline struct socket *tun_get_socket(struct file *f)
+{
+       return ERR_PTR(-EINVAL);
+}
+#endif /* CONFIG_TUN */
+#endif /* __KERNEL__ */
 #endif /* __IF_TUN_H */