bridge: Add a default_pvid sysfs attribute

This patch allows the user to set and retrieve default_pvid
value. A new value can only be stored when vlan filtering
is disabled.

Signed-off-by: Vladislav Yasevich <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/bridge/br_private.h

···
 #ifdef CONFIG_BRIDGE_VLAN_FILTERING
 	u8				vlan_enabled;
 	__be16				vlan_proto;
+	u16				default_pvid;
 	struct net_port_vlans __rcu	*vlan_info;
 #endif
 };
···
 int br_vlan_filter_toggle(struct net_bridge *br, unsigned long val);
 int br_vlan_set_proto(struct net_bridge *br, unsigned long val);
 void br_vlan_init(struct net_bridge *br);
+int br_vlan_set_default_pvid(struct net_bridge *br, unsigned long val);
 int nbp_vlan_add(struct net_bridge_port *port, u16 vid, u16 flags);
 int nbp_vlan_delete(struct net_bridge_port *port, u16 vid);
 void nbp_vlan_flush(struct net_bridge_port *port);

net/bridge/br_sysfs_br.c

···
 	return store_bridge_parm(d, buf, len, br_vlan_set_proto);
 }
 static DEVICE_ATTR_RW(vlan_protocol);
+
+static ssize_t default_pvid_show(struct device *d,
+				 struct device_attribute *attr,
+				 char *buf)
+{
+	struct net_bridge *br = to_bridge(d);
+	return sprintf(buf, "%d\n", br->default_pvid);
+}
+
+static ssize_t default_pvid_store(struct device *d,
+				  struct device_attribute *attr,
+				  const char *buf, size_t len)
+{
+	return store_bridge_parm(d, buf, len, br_vlan_set_default_pvid);
+}
+static DEVICE_ATTR_RW(default_pvid);
 #endif
 
 static struct attribute *bridge_attrs[] = {
···
 #ifdef CONFIG_BRIDGE_VLAN_FILTERING
 	&dev_attr_vlan_filtering.attr,
 	&dev_attr_vlan_protocol.attr,
+	&dev_attr_default_pvid.attr,
 #endif
 	NULL
 };

net/bridge/br_vlan.c

···
 	goto unlock;
 }
 
+int br_vlan_set_default_pvid(struct net_bridge *br, unsigned long val)
+{
+	u16 pvid = val;
+	int err = 0;
+
+	if (!val || val >= VLAN_VID_MASK)
+		return -EINVAL;
+
+	if (!rtnl_trylock())
+		return restart_syscall();
+
+	if (pvid == br->default_pvid)
+		goto unlock;
+
+	/* Only allow default pvid change when filtering is disabled */
+	if (br->vlan_enabled) {
+		pr_info_once("Please disable vlan filtering to change default_pvid\n");
+		err = -EPERM;
+		goto unlock;
+	}
+
+	br->default_pvid = pvid;
+
+unlock:
+	rtnl_unlock();
+	return err;
+}
+
 void br_vlan_init(struct net_bridge *br)
 {
 	br->vlan_proto = htons(ETH_P_8021Q);
+	br->default_pvid = 1;
 }
 
 /* Must be protected by RTNL.