tuntap: add ioctl to attach or detach a file form tuntap device

Sometimes usespace may need to active/deactive a queue, this could be done by
detaching and attaching a file from tuntap device.

This patch introduces a new ioctls - TUNSETQUEUE which could be used to do
this. Flag IFF_ATTACH_QUEUE were introduced to do attaching while
IFF_DETACH_QUEUE were introduced to do the detaching.
Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/tun.c

@@ -195,6 +195,15 @@ static u16 tun_select_queue(struct net_device *dev, struct sk_buff *skb)
 	return txq;
 }
 
+static inline bool tun_not_capable(struct tun_struct *tun)
+{
+	const struct cred *cred = current_cred();
+
+	return ((uid_valid(tun->owner) && !uid_eq(cred->euid, tun->owner)) ||
+		  (gid_valid(tun->group) && !in_egroup_p(tun->group))) &&
+		!capable(CAP_NET_ADMIN);
+}
+
 static void tun_set_real_num_queues(struct tun_struct *tun)
 {
 	netif_set_real_num_tx_queues(tun->dev, tun->numqueues);
@@ -1310,8 +1319,6 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
 
 	dev = __dev_get_by_name(net, ifr->ifr_name);
 	if (dev) {
-		const struct cred *cred = current_cred();
-
 		if (ifr->ifr_flags & IFF_TUN_EXCL)
 			return -EBUSY;
 		if ((ifr->ifr_flags & IFF_TUN) && dev->netdev_ops == &tun_netdev_ops)
@@ -1321,9 +1328,7 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
 		else
 			return -EINVAL;
 
-		if (((uid_valid(tun->owner) && !uid_eq(cred->euid, tun->owner)) ||
-		     (gid_valid(tun->group) && !in_egroup_p(tun->group))) &&
-		    !capable(CAP_NET_ADMIN))
+		if (tun_not_capable(tun))
 			return -EPERM;
 		err = security_tun_dev_attach(tfile->socket.sk);
 		if (err < 0)
@@ -1530,6 +1535,40 @@ static void tun_set_sndbuf(struct tun_struct *tun)
 	}
 }
 
+static int tun_set_queue(struct file *file, struct ifreq *ifr)
+{
+	struct tun_file *tfile = file->private_data;
+	struct tun_struct *tun;
+	struct net_device *dev;
+	int ret = 0;
+
+	rtnl_lock();
+
+	if (ifr->ifr_flags & IFF_ATTACH_QUEUE) {
+		dev = __dev_get_by_name(tfile->net, ifr->ifr_name);
+		if (!dev) {
+			ret = -EINVAL;
+			goto unlock;
+		}
+
+		tun = netdev_priv(dev);
+		if (dev->netdev_ops != &tap_netdev_ops &&
+			dev->netdev_ops != &tun_netdev_ops)
+			ret = -EINVAL;
+		else if (tun_not_capable(tun))
+			ret = -EPERM;
+		else
+			ret = tun_attach(tun, file);
+	} else if (ifr->ifr_flags & IFF_DETACH_QUEUE)
+		__tun_detach(tfile, false);
+	else
+		ret = -EINVAL;
+
+unlock:
+	rtnl_unlock();
+	return ret;
+}
+
 static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
 			    unsigned long arg, int ifreq_len)
 {
@@ -1543,7 +1582,7 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
 	int vnet_hdr_sz;
 	int ret;
 
-	if (cmd == TUNSETIFF || _IOC_TYPE(cmd) == 0x89) {
+	if (cmd == TUNSETIFF || cmd == TUNSETQUEUE || _IOC_TYPE(cmd) == 0x89) {
 		if (copy_from_user(&ifr, argp, ifreq_len))
 			return -EFAULT;
 	} else {
@@ -1554,9 +1593,10 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
 		 * This is needed because we never checked for invalid flags on
 		 * TUNSETIFF. */
 		return put_user(IFF_TUN | IFF_TAP | IFF_NO_PI | IFF_ONE_QUEUE |
-				IFF_VNET_HDR,
+				IFF_VNET_HDR | IFF_MULTI_QUEUE,
 				(unsigned int __user*)argp);
-	}
+	} else if (cmd == TUNSETQUEUE)
+		return tun_set_queue(file, &ifr);
 
 	ret = 0;
 	rtnl_lock();

include/uapi/linux/if_tun.h

@@ -54,6 +54,7 @@
 #define TUNDETACHFILTER _IOW('T', 214, struct sock_fprog)
 #define TUNGETVNETHDRSZ _IOR('T', 215, int)
 #define TUNSETVNETHDRSZ _IOW('T', 216, int)
+#define TUNSETQUEUE  _IOW('T', 217, int)
 
 /* TUNSETIFF ifr flags */
 #define IFF_TUN		0x0001
@@ -63,6 +64,8 @@
 #define IFF_VNET_HDR	0x4000
 #define IFF_TUN_EXCL	0x8000
 #define IFF_MULTI_QUEUE 0x0100
+#define IFF_ATTACH_QUEUE 0x0200
+#define IFF_DETACH_QUEUE 0x0400
 
 /* Features for GSO (TUNSETOFFLOAD). */
 #define TUN_F_CSUM	0x01	/* You can hand me unchecksummed packets. */