net-sysfs: expose physical switch id for particular device

Signed-off-by: Jiri Pirko <jiri@resnulli.us>
Reviewed-by: Thomas Graf <tgraf@suug.ch>
Acked-by: John Fastabend <john.r.fastabend@intel.com>
Acked-by: Andy Gospodarek <gospo@cumulusnetworks.com>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/ABI/testing/sysfs-class-net

@@ -216,3 +216,11 @@ Contact:	netdev@vger.kernel.org
 Description:
 		Indicates the interface protocol type as a decimal value. See
 		include/uapi/linux/if_arp.h for all possible values.
+
+What:		/sys/class/net/<iface>/phys_switch_id
+Date:		November 2014
+KernelVersion:	3.19
+Contact:	netdev@vger.kernel.org
+Description:
+		Indicates the unique physical switch identifier of a switch this
+		port belongs to, as a string.

net/core/net-sysfs.c

@@ -12,6 +12,7 @@
 #include <linux/capability.h>
 #include <linux/kernel.h>
 #include <linux/netdevice.h>
+#include <net/switchdev.h>
 #include <linux/if_arp.h>
 #include <linux/slab.h>
 #include <linux/nsproxy.h>
@@ -416,6 +417,28 @@ static ssize_t phys_port_id_show(struct device *dev,
 }
 static DEVICE_ATTR_RO(phys_port_id);
 
+static ssize_t phys_switch_id_show(struct device *dev,
+				   struct device_attribute *attr, char *buf)
+{
+	struct net_device *netdev = to_net_dev(dev);
+	ssize_t ret = -EINVAL;
+
+	if (!rtnl_trylock())
+		return restart_syscall();
+
+	if (dev_isalive(netdev)) {
+		struct netdev_phys_item_id ppid;
+
+		ret = netdev_switch_parent_id_get(netdev, &ppid);
+		if (!ret)
+			ret = sprintf(buf, "%*phN\n", ppid.id_len, ppid.id);
+	}
+	rtnl_unlock();
+
+	return ret;
+}
+static DEVICE_ATTR_RO(phys_switch_id);
+
 static struct attribute *net_class_attrs[] = {
 	&dev_attr_netdev_group.attr,
 	&dev_attr_type.attr,
@@ -441,6 +464,7 @@ static struct attribute *net_class_attrs[] = {
 	&dev_attr_tx_queue_len.attr,
 	&dev_attr_gro_flush_timeout.attr,
 	&dev_attr_phys_port_id.attr,
+	&dev_attr_phys_switch_id.attr,
 	NULL,
 };
 ATTRIBUTE_GROUPS(net_class);