[C] [PATCH] tun: implement carrier change

[Kai-Heng Feng]

From: Nicolas Dichtel <nicolas.dichtel at 6wind.com>

BugLink: https://bugs.launchpad.net/bugs/1806392

The userspace may need to control the carrier state.

Signed-off-by: Nicolas Dichtel <nicolas.dichtel at 6wind.com>
Signed-off-by: Didier Pallard <didier.pallard at 6wind.com>
Signed-off-by: David S. Miller <davem at davemloft.net>
(cherry picked from commit 26d31925cd5ea4b5b168ed538b0326d63ccbb384)
Signed-off-by: Kai-Heng Feng <kai.heng.feng at canonical.com>
---
 drivers/net/tun.c           | 27 ++++++++++++++++++++++++++-
 include/uapi/linux/if_tun.h |  1 +
 2 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 546081993ecf..694a27da7278 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1274,6 +1274,21 @@ static int tun_xdp(struct net_device *dev, struct netdev_bpf *xdp)
 	}
 }
 
+static int tun_net_change_carrier(struct net_device *dev, bool new_carrier)
+{
+	if (new_carrier) {
+		struct tun_struct *tun = netdev_priv(dev);
+
+		if (!tun->numqueues)
+			return -EPERM;
+
+		netif_carrier_on(dev);
+	} else {
+		netif_carrier_off(dev);
+	}
+	return 0;
+}
+
 static const struct net_device_ops tun_netdev_ops = {
 	.ndo_uninit		= tun_net_uninit,
 	.ndo_open		= tun_net_open,
@@ -1286,6 +1301,7 @@ static const struct net_device_ops tun_netdev_ops = {
 #endif
 	.ndo_set_rx_headroom	= tun_set_headroom,
 	.ndo_get_stats64	= tun_net_get_stats64,
+	.ndo_change_carrier	= tun_net_change_carrier,
 };
 
 static void __tun_xdp_flush_tfile(struct tun_file *tfile)
@@ -1371,6 +1387,7 @@ static const struct net_device_ops tap_netdev_ops = {
 	.ndo_get_stats64	= tun_net_get_stats64,
 	.ndo_bpf		= tun_xdp,
 	.ndo_xdp_xmit		= tun_xdp_xmit,
+	.ndo_change_carrier	= tun_net_change_carrier,
 };
 
 static void tun_flow_init(struct tun_struct *tun)
@@ -2872,12 +2889,12 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
 	struct net *net = sock_net(&tfile->sk);
 	struct tun_struct *tun;
 	void __user* argp = (void __user*)arg;
+	unsigned int ifindex, carrier;
 	struct ifreq ifr;
 	kuid_t owner;
 	kgid_t group;
 	int sndbuf;
 	int vnet_hdr_sz;
-	unsigned int ifindex;
 	int le;
 	int ret;
 	bool do_notify = false;
@@ -3161,6 +3178,14 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
 		ret = tun_set_ebpf(tun, &tun->filter_prog, argp);
 		break;
 
+	case TUNSETCARRIER:
+		ret = -EFAULT;
+		if (copy_from_user(&carrier, argp, sizeof(carrier)))
+			goto unlock;
+
+		ret = tun_net_change_carrier(tun->dev, (bool)carrier);
+		break;
+
 	default:
 		ret = -EINVAL;
 		break;
diff --git a/include/uapi/linux/if_tun.h b/include/uapi/linux/if_tun.h
index ee432cd3018c..23a6753b37df 100644
--- a/include/uapi/linux/if_tun.h
+++ b/include/uapi/linux/if_tun.h
@@ -59,6 +59,7 @@
 #define TUNGETVNETBE _IOR('T', 223, int)
 #define TUNSETSTEERINGEBPF _IOR('T', 224, int)
 #define TUNSETFILTEREBPF _IOR('T', 225, int)
+#define TUNSETCARRIER _IOW('T', 226, int)
 
 /* TUNSETIFF ifr flags */
 #define IFF_TUN		0x0001
-- 
2.17.1