net: sysfs: Implement is_visible for phys_(port_id, port_name, switch_id)

phys_port_id_show, phys_port_name_show and phys_switch_id_show would
return -EOPNOTSUPP if the netdev didn't implement the corresponding
method.

There is no point in creating these files if they are unsupported.

Put these attributes in netdev_phys_group and implement the is_visible
method. make phys_(port_id, port_name, switch_id) invisible if the netdev
dosen't implement the corresponding method.

Signed-off-by: Yajun Deng <[e-mail]>
Reviewed-by: Simon Horman <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

include/linux/netdevice.h

···
 	struct dm_hw_stat_delta __rcu *dm_private;
 #endif
 	struct device		dev;
-	const struct attribute_group *sysfs_groups[4];
+	const struct attribute_group *sysfs_groups[5];
 	const struct attribute_group *sysfs_rx_queue_group;
 
 	const struct rtnl_link_ops *rtnl_link_ops;

net/core/net-sysfs.c

···
 	struct netdev_phys_item_id ppid;
 	ssize_t ret;
 
-	/* The check is also done in dev_get_phys_port_id; this helps returning
-	 * early without hitting the locking section below.
-	 */
-	if (!netdev->netdev_ops->ndo_get_phys_port_id)
-		return -EOPNOTSUPP;
-
 	ret = sysfs_rtnl_lock(&dev->kobj, &attr->attr, netdev);
 	if (ret)
 		return ret;
···
 	struct net_device *netdev = to_net_dev(dev);
 	char name[IFNAMSIZ];
 	ssize_t ret;
-
-	/* The checks are also done in dev_get_phys_port_name; this helps
-	 * returning early without hitting the locking section below.
-	 */
-	if (!netdev->netdev_ops->ndo_get_phys_port_name &&
-	    !netdev->devlink_port)
-		return -EOPNOTSUPP;
 
 	ret = sysfs_rtnl_lock(&dev->kobj, &attr->attr, netdev);
 	if (ret)
···
 	struct netdev_phys_item_id ppid = { };
 	ssize_t ret;
 
-	/* The checks are also done in dev_get_phys_port_name; this helps
-	 * returning early without hitting the locking section below. This works
-	 * because recurse is false when calling dev_get_port_parent_id.
-	 */
-	if (!netdev->netdev_ops->ndo_get_port_parent_id &&
-	    !netdev->devlink_port)
-		return -EOPNOTSUPP;
-
 	ret = sysfs_rtnl_lock(&dev->kobj, &attr->attr, netdev);
 	if (ret)
 		return ret;
···
 	return ret;
 }
 static DEVICE_ATTR_RO(phys_switch_id);
+
+static struct attribute *netdev_phys_attrs[] __ro_after_init = {
+	&dev_attr_phys_port_id.attr,
+	&dev_attr_phys_port_name.attr,
+	&dev_attr_phys_switch_id.attr,
+	NULL,
+};
+
+static umode_t netdev_phys_is_visible(struct kobject *kobj,
+				      struct attribute *attr, int index)
+{
+	struct device *dev = kobj_to_dev(kobj);
+	struct net_device *netdev = to_net_dev(dev);
+
+	if (attr == &dev_attr_phys_port_id.attr) {
+		if (!netdev->netdev_ops->ndo_get_phys_port_id)
+			return 0;
+	} else if (attr == &dev_attr_phys_port_name.attr) {
+		if (!netdev->netdev_ops->ndo_get_phys_port_name &&
+		    !netdev->devlink_port)
+			return 0;
+	} else if (attr == &dev_attr_phys_switch_id.attr) {
+		if (!netdev->netdev_ops->ndo_get_port_parent_id &&
+		    !netdev->devlink_port)
+			return 0;
+	}
+
+	return attr->mode;
+}
+
+static const struct attribute_group netdev_phys_group = {
+	.attrs = netdev_phys_attrs,
+	.is_visible = netdev_phys_is_visible,
+};
 
 static ssize_t threaded_show(struct device *dev,
 			     struct device_attribute *attr, char *buf)
···
 	&dev_attr_tx_queue_len.attr,
 	&dev_attr_gro_flush_timeout.attr,
 	&dev_attr_napi_defer_hard_irqs.attr,
-	&dev_attr_phys_port_id.attr,
-	&dev_attr_phys_port_name.attr,
-	&dev_attr_phys_switch_id.attr,
 	&dev_attr_proto_down.attr,
 	&dev_attr_carrier_up_count.attr,
 	&dev_attr_carrier_down_count.attr,
···
 		groups++;
 
 	*groups++ = &netstat_group;
+	*groups++ = &netdev_phys_group;
 
 	if (wireless_group_needed(ndev))
 		*groups++ = &wireless_group;