Linux Ethernet Bridging - Aug 2009 - [Bridge] [PATCH] net/bridge: Add 'hairpin' port forwarding mode

This patch adds a 'hairpin' (also called 'reflective relay')
mode
port configuration to the Linux Ethernet bridge kernel module.
A bridge supporting hairpin forwarding mode can send frames back
out through the port the frame was received on.

Hairpin mode is required to support basic VEPA (Virtual
Ethernet Port Aggregator) capabilities.

You can find additional information on VEPA here:
http://tech.groups.yahoo.com/group/evb/
http://www.ieee802.org/1/files/public/docs2009/new-hudson-vepa_seminar-20090514d.pdf
http://www.internet2.edu/presentations/jt2009jul/20090719-congdon.pdf

An additional patch 'bridge-utils: Add 'hairpin' port forwarding
mode'
is provided to allow configuring hairpin mode from userspace tools.

Signed-off-by: Paul Congdon <paul.congdon at hp.com>
Signed-off-by: Anna Fischer <anna.fischer at hp.com>

---

 net/bridge/br_forward.c  |    3 ++-
 net/bridge/br_if.c       |    1 +
 net/bridge/br_private.h  |    3 +++
 net/bridge/br_sysfs_if.c |   17 +++++++++++++++++
 4 files changed, 23 insertions(+), 1 deletions(-)

diff --git a/net/bridge/br_forward.c b/net/bridge/br_forward.c
index d2c27c8..bc1704a 100644
--- a/net/bridge/br_forward.c
+++ b/net/bridge/br_forward.c
@@ -22,7 +22,8 @@
 static inline int should_deliver(const struct net_bridge_port *p,
 				 const struct sk_buff *skb)
 {
-	return (skb->dev != p->dev && p->state ==
BR_STATE_FORWARDING);
+	return (((p->flags & BR_HAIRPIN_MODE) || skb->dev != p->dev)
&&
+		p->state == BR_STATE_FORWARDING);
 }
 
 static inline unsigned packet_length(const struct sk_buff *skb)
diff --git a/net/bridge/br_if.c b/net/bridge/br_if.c
index eb404dc..e486f1f 100644
--- a/net/bridge/br_if.c
+++ b/net/bridge/br_if.c
@@ -256,6 +256,7 @@ static struct net_bridge_port *new_nbp(struct net_bridge
*br,
 	p->path_cost = port_cost(dev);
 	p->priority = 0x8000 >> BR_PORT_BITS;
 	p->port_no = index;
+	p->flags = 0;
 	br_init_port(p);
 	p->state = BR_STATE_DISABLED;
 	br_stp_port_timer_init(p);
diff --git a/net/bridge/br_private.h b/net/bridge/br_private.h
index d5b5537..8319247 100644
--- a/net/bridge/br_private.h
+++ b/net/bridge/br_private.h
@@ -81,6 +81,9 @@ struct net_bridge_port
 	struct timer_list		message_age_timer;
 	struct kobject			kobj;
 	struct rcu_head			rcu;
+
+	unsigned long 			flags;
+#define BR_HAIRPIN_MODE		0x00000001
 };
 
 struct net_bridge
diff --git a/net/bridge/br_sysfs_if.c b/net/bridge/br_sysfs_if.c
index 4a3cdf8..820643a 100644
--- a/net/bridge/br_sysfs_if.c
+++ b/net/bridge/br_sysfs_if.c
@@ -143,6 +143,22 @@ static ssize_t store_flush(struct net_bridge_port *p,
unsigned long v)
 }
 static BRPORT_ATTR(flush, S_IWUSR, NULL, store_flush);
 
+static ssize_t show_hairpin_mode(struct net_bridge_port *p, char *buf)
+{
+	int hairpin_mode = (p->flags & BR_HAIRPIN_MODE) ? 1 : 0;
+	return sprintf(buf, "%d\n", hairpin_mode);
+}
+static ssize_t store_hairpin_mode(struct net_bridge_port *p, unsigned long v)
+{
+	if (v)
+		p->flags |= BR_HAIRPIN_MODE;
+	else
+		p->flags &= ~BR_HAIRPIN_MODE;
+	return 0;
+}
+static BRPORT_ATTR(hairpin_mode, S_IRUGO | S_IWUSR,
+		   show_hairpin_mode, store_hairpin_mode);
+
 static struct brport_attribute *brport_attrs[] = {
 	&brport_attr_path_cost,
 	&brport_attr_priority,
@@ -159,6 +175,7 @@ static struct brport_attribute *brport_attrs[] = {
 	&brport_attr_forward_delay_timer,
 	&brport_attr_hold_timer,
 	&brport_attr_flush,
+	&brport_attr_hairpin_mode,
 	NULL
 };

On Thursday 13 August 2009, Fischer, Anna wrote:
> This patch adds a 'hairpin' (also called 'reflective
relay') mode
> port configuration to the Linux Ethernet bridge kernel module.
> A bridge supporting hairpin forwarding mode can send frames back
> out through the port the frame was received on.
> 
> Hairpin mode is required to support basic VEPA (Virtual
> Ethernet Port Aggregator) capabilities.
> 
> You can find additional information on VEPA here:
> http://tech.groups.yahoo.com/group/evb/
>
http://www.ieee802.org/1/files/public/docs2009/new-hudson-vepa_seminar-20090514d.pdf
> http://www.internet2.edu/presentations/jt2009jul/20090719-congdon.pdf
> 
> An additional patch 'bridge-utils: Add 'hairpin' port
forwarding mode'
> is provided to allow configuring hairpin mode from userspace tools.
> 
> Signed-off-by: Paul Congdon <paul.congdon at hp.com>
> Signed-off-by: Anna Fischer <anna.fischer at hp.com>
Acked-by: Arnd Bergmann <arnd at arndb.de>

> diff --git a/net/bridge/br_if.c b/net/bridge/br_if.c
> index eb404dc..e486f1f 100644
> --- a/net/bridge/br_if.c
> +++ b/net/bridge/br_if.c
> @@ -256,6 +256,7 @@ static struct net_bridge_port *new_nbp(struct
net_bridge *br,
>  	p->path_cost = port_cost(dev);
>  	p->priority = 0x8000 >> BR_PORT_BITS;
>  	p->port_no = index;
> +	p->flags = 0;
>  	br_init_port(p);
>  	p->state = BR_STATE_DISABLED;
>  	br_stp_port_timer_init(p);
Minor nit. this is unnecessary since the structure is allocated with kzalloc.

From: "Fischer, Anna" <anna.fischer at hp.com>
Date: Thu, 13 Aug 2009 16:55:16 +0000
> This patch adds a 'hairpin' (also called 'reflective
relay') mode
> port configuration to the Linux Ethernet bridge kernel module.
> A bridge supporting hairpin forwarding mode can send frames back
> out through the port the frame was received on.
> 
> Hairpin mode is required to support basic VEPA (Virtual
> Ethernet Port Aggregator) capabilities.
> 
> You can find additional information on VEPA here:
> http://tech.groups.yahoo.com/group/evb/
>
http://www.ieee802.org/1/files/public/docs2009/new-hudson-vepa_seminar-20090514d.pdf
> http://www.internet2.edu/presentations/jt2009jul/20090719-congdon.pdf
> 
> An additional patch 'bridge-utils: Add 'hairpin' port
forwarding mode'
> is provided to allow configuring hairpin mode from userspace tools.
> 
> Signed-off-by: Paul Congdon <paul.congdon at hp.com>
> Signed-off-by: Anna Fischer <anna.fischer at hp.com>
Applied to net-next-2.6

Do we need to add this to block Spanning Tree from being enabled
with hairpin mode? I am not sure what the exact usage of hairpin
mode and if it is possible to create loops and get STP confusion.

For comment only, do not apply as is.


--- a/net/bridge/br_ioctl.c	2009-08-14 14:28:19.917690805 -0700
+++ b/net/bridge/br_ioctl.c	2009-08-14 14:29:54.078271361 -0700
@@ -259,8 +259,7 @@ static int old_dev_ioctl(struct net_devi
 		if (!capable(CAP_NET_ADMIN))
 			return -EPERM;
 
-		br_stp_set_enabled(br, args[1]);
-		return 0;
+		return br_stp_set_enabled(br, args[1]);
 
 	case BRCTL_SET_BRIDGE_PRIORITY:
 		if (!capable(CAP_NET_ADMIN))
--- a/net/bridge/br_stp_if.c	2009-08-14 14:24:30.022315573 -0700
+++ b/net/bridge/br_stp_if.c	2009-08-14 14:35:25.819566113 -0700
@@ -160,17 +160,26 @@ static void br_stp_stop(struct net_bridg
 	br->stp_enabled = BR_NO_STP;
 }
 
-void br_stp_set_enabled(struct net_bridge *br, unsigned long val)
+int br_stp_set_enabled(struct net_bridge *br, unsigned long val)
 {
 	ASSERT_RTNL();
 
 	if (val) {
+		struct net_bridge_port *p;
+		list_for_each_entry_rcu(p, &br->port_list, list) {
+			if (p->flags & BR_HAIRPIN_MODE)
+				return -EINVAL;
+		}
+
+
 		if (br->stp_enabled == BR_NO_STP)
 			br_stp_start(br);
 	} else {
 		if (br->stp_enabled != BR_NO_STP)
 			br_stp_stop(br);
 	}
+
+	return 0;
 }
 
 /* called under bridge lock */
--- a/net/bridge/br_sysfs_br.c	2009-08-14 14:24:36.874256194 -0700
+++ b/net/bridge/br_sysfs_br.c	2009-08-14 14:33:26.025441102 -0700
@@ -164,6 +164,7 @@ static ssize_t store_stp_state(struct de
 	struct net_bridge *br = to_bridge(d);
 	char *endp;
 	unsigned long val;
+	int ret;
 
 	if (!capable(CAP_NET_ADMIN))
 		return -EPERM;
@@ -174,10 +175,11 @@ static ssize_t store_stp_state(struct de
 
 	if (!rtnl_trylock())
 		return restart_syscall();
-	br_stp_set_enabled(br, val);
+
+	ret = br_stp_set_enabled(br, val);
 	rtnl_unlock();
 
-	return len;
+	return (ret == 0) ? len : ret;
 }
 static DEVICE_ATTR(stp_state, S_IRUGO | S_IWUSR, show_stp_state,
 		   store_stp_state);
--- a/net/bridge/br_sysfs_if.c	2009-08-14 14:24:36.888356879 -0700
+++ b/net/bridge/br_sysfs_if.c	2009-08-14 14:34:55.339272738 -0700
@@ -150,10 +150,13 @@ static ssize_t show_hairpin_mode(struct 
 }
 static ssize_t store_hairpin_mode(struct net_bridge_port *p, unsigned long v)
 {
-	if (v)
+	if (!v)
+		p->flags &= ~BR_HAIRPIN_MODE;
+	else if (p->br->stp_enabled == BR_NO_STP)
 		p->flags |= BR_HAIRPIN_MODE;
 	else
-		p->flags &= ~BR_HAIRPIN_MODE;
+		return -EINVAL;
+
 	return 0;
 }
 static BRPORT_ATTR(hairpin_mode, S_IRUGO | S_IWUSR,
--- a/net/bridge/br_private.h	2009-08-14 14:34:05.263278817 -0700
+++ b/net/bridge/br_private.h	2009-08-14 14:34:15.717297908 -0700
@@ -218,7 +218,7 @@ extern void br_become_designated_port(st
 /* br_stp_if.c */
 extern void br_stp_enable_bridge(struct net_bridge *br);
 extern void br_stp_disable_bridge(struct net_bridge *br);
-extern void br_stp_set_enabled(struct net_bridge *br, unsigned long val);
+extern int br_stp_set_enabled(struct net_bridge *br, unsigned long val);
 extern void br_stp_enable_port(struct net_bridge_port *p);
 extern void br_stp_disable_port(struct net_bridge_port *p);
 extern void br_stp_recalculate_bridge_id(struct net_bridge *br);