From: Jason Wang <jasowang@redhat.com>
Date: Wed, 17 May 2017 12:14:43 +0800
Subject: tun: support receiving skb through msg_control
Patch-mainline: v4.13-rc1
Git-commit: ac77cfd4258fb8174766a92d118436da7f9dabf1
References: bsc#1109837

This patch makes tun_recvmsg() can receive from skb from its caller
through msg_control. Vhost_net will be the first user.

Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
---
 drivers/net/tun.c |   18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1510,9 +1510,8 @@ out:
 
 static ssize_t tun_do_read(struct tun_struct *tun, struct tun_file *tfile,
 			   struct iov_iter *to,
-			   int noblock)
+			   int noblock, struct sk_buff *skb)
 {
-	struct sk_buff *skb;
 	ssize_t ret;
 	int err;
 
@@ -1521,10 +1520,12 @@ static ssize_t tun_do_read(struct tun_st
 	if (!iov_iter_count(to))
 		return 0;
 
-	/* Read frames from ring */
-	skb = tun_ring_recv(tfile, noblock, &err);
-	if (!skb)
-		return err;
+	if (!skb) {
+		/* Read frames from ring */
+		skb = tun_ring_recv(tfile, noblock, &err);
+		if (!skb)
+			return err;
+	}
 
 	ret = tun_put_user(tun, tfile, skb, to);
 	if (unlikely(ret < 0))
@@ -1544,7 +1545,7 @@ static ssize_t tun_chr_read_iter(struct
 
 	if (!tun)
 		return -EBADFD;
-	ret = tun_do_read(tun, tfile, to, file->f_flags & O_NONBLOCK);
+	ret = tun_do_read(tun, tfile, to, file->f_flags & O_NONBLOCK, NULL);
 	ret = min_t(ssize_t, ret, len);
 	if (ret > 0)
 		iocb->ki_pos = ret;
@@ -1646,7 +1647,8 @@ static int tun_recvmsg(struct socket *so
 					 SOL_PACKET, TUN_TX_TIMESTAMP);
 		goto out;
 	}
-	ret = tun_do_read(tun, tfile, &m->msg_iter, flags & MSG_DONTWAIT);
+	ret = tun_do_read(tun, tfile, &m->msg_iter, flags & MSG_DONTWAIT,
+			  m->msg_control);
 	if (ret > (ssize_t)total_len) {
 		m->msg_flags |= MSG_TRUNC;
 		ret = flags & MSG_TRUNC ? ret : total_len;