[PATCH net-next V2 3/3] tun: add eBPF based queue selection method

[Jason Wang]

This patch introduces an eBPF based queue selection method based on
the flow steering policy ops. Userspace could load an eBPF program
through TUNSETSTEERINGEBPF. This gives much more flexibility compare
to simple but hard coded policy in kernel.

Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
---
 drivers/net/tun.c           | 79 ++++++++++++++++++++++++++++++++++++++++++++-
 include/uapi/linux/if_tun.h |  2 ++
 2 files changed, 80 insertions(+), 1 deletion(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index ab109ff..4bdde21 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -191,6 +191,20 @@ struct tun_steering_ops {
 			 u32 data);
 };
 
+void tun_steering_xmit_nop(struct tun_struct *tun, struct sk_buff *skb)
+{
+}
+
+u32 tun_steering_pre_rx_nop(struct tun_struct *tun, struct sk_buff *skb)
+{
+	return 0;
+}
+
+void tun_steering_post_rx_nop(struct tun_struct *tun, struct tun_file *tfile,
+			      u32 data)
+{
+}
+
 struct tun_flow_entry {
 	struct hlist_node hash_link;
 	struct rcu_head rcu;
@@ -241,6 +255,7 @@ struct tun_struct {
 	u32 rx_batched;
 	struct tun_pcpu_stats __percpu *pcpu_stats;
 	struct bpf_prog __rcu *xdp_prog;
+	struct bpf_prog __rcu *steering_prog;
 	struct tun_steering_ops *steering_ops;
 };
 
@@ -576,6 +591,19 @@ static u16 tun_automq_select_queue(struct tun_struct *tun, struct sk_buff *skb)
 	return txq;
 }
 
+static u16 tun_ebpf_select_queue(struct tun_struct *tun, struct sk_buff *skb)
+{
+	struct bpf_prog *prog;
+	u16 ret = 0;
+
+	rcu_read_lock();
+	prog = rcu_dereference(tun->steering_prog);
+	if (prog)
+		ret = bpf_prog_run_clear_cb(prog, skb);
+	rcu_read_unlock();
+
+	return ret % tun->numqueues;
+}
 static u16 tun_select_queue(struct net_device *dev, struct sk_buff *skb,
 			    void *accel_priv, select_queue_fallback_t fallback)
 {
@@ -2017,6 +2045,20 @@ static ssize_t tun_chr_read_iter(struct kiocb *iocb, struct iov_iter *to)
 	return ret;
 }
 
+static void __tun_set_steering_ebpf(struct tun_struct *tun,
+				    struct bpf_prog *new)
+{
+	struct bpf_prog *old;
+
+	old = rtnl_dereference(tun->steering_prog);
+	rcu_assign_pointer(tun->steering_prog, new);
+
+	if (old) {
+		synchronize_net();
+		bpf_prog_destroy(old);
+	}
+}
+
 static void tun_free_netdev(struct net_device *dev)
 {
 	struct tun_struct *tun = netdev_priv(dev);
@@ -2025,6 +2067,7 @@ static void tun_free_netdev(struct net_device *dev)
 	free_percpu(tun->pcpu_stats);
 	tun_flow_uninit(tun);
 	security_tun_dev_free_security(tun->security);
+	__tun_set_steering_ebpf(tun, NULL);
 }
 
 static void tun_setup(struct net_device *dev)
@@ -2159,6 +2202,13 @@ static struct tun_steering_ops tun_automq_ops = {
 	.post_rx = tun_automq_post_rx,
 };
 
+static struct tun_steering_ops tun_ebpf_ops = {
+	.select_queue = tun_ebpf_select_queue,
+	.xmit = tun_steering_xmit_nop,
+	.pre_rx = tun_steering_pre_rx_nop,
+	.post_rx = tun_steering_post_rx_nop,
+};
+
 static int tun_flags(struct tun_struct *tun)
 {
 	return tun->flags & (TUN_FEATURES | IFF_PERSIST | IFF_TUN | IFF_TAP);
@@ -2311,6 +2361,7 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
 		tun->filter_attached = false;
 		tun->sndbuf = tfile->socket.sk->sk_sndbuf;
 		tun->rx_batched = 0;
+		RCU_INIT_POINTER(tun->steering_prog, NULL);
 
 		tun->pcpu_stats = netdev_alloc_pcpu_stats(struct tun_pcpu_stats);
 		if (!tun->pcpu_stats) {
@@ -2503,6 +2554,23 @@ static int tun_set_queue(struct file *file, struct ifreq *ifr)
 	return ret;
 }
 
+static int tun_set_steering_ebpf(struct tun_struct *tun, void __user *data)
+{
+	struct bpf_prog *prog;
+	u32 fd;
+
+	if (copy_from_user(&fd, data, sizeof(fd)))
+		return -EFAULT;
+
+	prog = bpf_prog_get_type(fd, BPF_PROG_TYPE_SOCKET_FILTER);
+	if (IS_ERR(prog))
+		return PTR_ERR(prog);
+
+	__tun_set_steering_ebpf(tun, prog);
+
+	return 0;
+}
+
 static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
 			    unsigned long arg, int ifreq_len)
 {
@@ -2785,6 +2853,9 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
 		case TUN_STEERING_AUTOMQ:
 			tun->steering_ops = &tun_automq_ops;
 			break;
+		case TUN_STEERING_EBPF:
+			tun->steering_ops = &tun_ebpf_ops;
+			break;
 		default:
 			ret = -EFAULT;
 		}
@@ -2794,6 +2865,8 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
 		ret = 0;
 		if (tun->steering_ops == &tun_automq_ops)
 			steering = TUN_STEERING_AUTOMQ;
+		else if (tun->steering_ops == &tun_ebpf_ops)
+			steering = TUN_STEERING_EBPF;
 		else
 			BUG();
 		if (copy_to_user(argp, &steering, sizeof(steering)))
@@ -2802,11 +2875,15 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
 
 	case TUNGETSTEERINGFEATURES:
 		ret = 0;
-		steering = TUN_STEERING_AUTOMQ;
+		steering = TUN_STEERING_AUTOMQ | TUN_STEERING_EBPF;
 		if (copy_to_user(argp, &steering, sizeof(steering)))
 			ret = -EFAULT;
 		break;
 
+	case TUNSETSTEERINGEBPF:
+		ret = tun_set_steering_ebpf(tun, argp);
+		break;
+
 	default:
 		ret = -EINVAL;
 		break;
diff --git a/include/uapi/linux/if_tun.h b/include/uapi/linux/if_tun.h
index 109760e..927f7e4 100644
--- a/include/uapi/linux/if_tun.h
+++ b/include/uapi/linux/if_tun.h
@@ -59,6 +59,7 @@
 #define TUNSETSTEERING _IOW('T', 224, unsigned int)
 #define TUNGETSTEERING _IOR('T', 225, unsigned int)
 #define TUNGETSTEERINGFEATURES _IOR('T', 226, unsigned int)
+#define TUNSETSTEERINGEBPF _IOR('T', 227, int)
 
 /* TUNSETIFF ifr flags */
 #define IFF_TUN		0x0001
@@ -112,5 +113,6 @@ struct tun_filter {
 };
 
 #define TUN_STEERING_AUTOMQ 0x01 /* Automatic flow steering */
+#define TUN_STEERING_EBPF   0x02 /* eBPF based flow steering */
 
 #endif /* _UAPI__IF_TUN_H */
-- 
2.7.4