net: network device name ifalias support

This patch add support for keeping an additional character alias
associated with an network interface. This is useful for maintaining
the SNMP ifAlias value which is a user defined value. Routers use this
to hold information like which circuit or line it is connected to. It
is just an arbitrary text label on the network device.

There are two exposed interfaces with this patch, the value can be
read/written either via netlink or sysfs.

This could be maintained just by the snmp daemon, but it is more
generally useful for other management tools, and the kernel is good
place to act as an agreed upon interface to store it.
Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/if.h

@@ -24,6 +24,7 @@
 #include <linux/compiler.h>		/* for "__user" et al           */
 
 #define	IFNAMSIZ	16
+#define	IFALIASZ	256
 #include <linux/hdlc/ioctl.h>
 
 /* Standard interface flags (netdevice->flags). */

include/linux/if_link.h

@@ -79,6 +79,7 @@ enum
 	IFLA_LINKINFO,
 #define IFLA_LINKINFO IFLA_LINKINFO
 	IFLA_NET_NS_PID,
+	IFLA_IFALIAS,
 	__IFLA_MAX
 };
 

include/linux/netdevice.h

@@ -471,6 +471,8 @@ struct net_device
 	char			name[IFNAMSIZ];
 	/* device name hash chain */
 	struct hlist_node	name_hlist;
+	/* snmp alias */
+	char 			*ifalias;
 
 	/*
 	 *	I/O specific fields
@@ -1224,6 +1226,7 @@ extern int		dev_ethtool(struct net *net, struct ifreq *);
 extern unsigned		dev_get_flags(const struct net_device *);
 extern int		dev_change_flags(struct net_device *, unsigned);
 extern int		dev_change_name(struct net_device *, char *);
+extern int		dev_set_alias(struct net_device *, const char *, size_t);
 extern int		dev_change_net_namespace(struct net_device *,
 						 struct net *, const char *);
 extern int		dev_set_mtu(struct net_device *, int);

net/core/dev.c

@@ -953,6 +953,29 @@ rollback:
 	return err;
 }
 
+/**
+ *	dev_set_alias - change ifalias of a device
+ *	@dev: device
+ *	@alias: name up to IFALIASZ
+ *
+ *	Set ifalias for a device,
+ */
+int dev_set_alias(struct net_device *dev, const char *alias, size_t len)
+{
+	ASSERT_RTNL();
+
+	if (len >= IFALIASZ)
+		return -EINVAL;
+
+	dev->ifalias = krealloc(dev->ifalias, len+1, GFP_KERNEL);
+	if (!dev->ifalias)
+		return -ENOMEM;
+
+	strlcpy(dev->ifalias, alias, len+1);
+	return len;
+}
+
+
 /**
  *	netdev_features_change - device changes features
  *	@dev: device to cause notification

net/core/net-sysfs.c

@@ -209,9 +209,44 @@ static ssize_t store_tx_queue_len(struct device *dev,
 	return netdev_store(dev, attr, buf, len, change_tx_queue_len);
 }
 
+static ssize_t store_ifalias(struct device *dev, struct device_attribute *attr,
+			     const char *buf, size_t len)
+{
+	struct net_device *netdev = to_net_dev(dev);
+	size_t count = len;
+	ssize_t ret;
+
+	if (!capable(CAP_NET_ADMIN))
+		return -EPERM;
+
+	/* ignore trailing newline */
+	if (len >  0 && buf[len - 1] == '\n')
+		--count;
+
+	rtnl_lock();
+	ret = dev_set_alias(netdev, buf, count);
+	rtnl_unlock();
+
+	return ret < 0 ? ret : len;
+}
+
+static ssize_t show_ifalias(struct device *dev,
+			    struct device_attribute *attr, char *buf)
+{
+	const struct net_device *netdev = to_net_dev(dev);
+	ssize_t ret = 0;
+
+	rtnl_lock();
+	if (netdev->ifalias)
+		ret = sprintf(buf, "%s\n", netdev->ifalias);
+	rtnl_unlock();
+	return ret;
+}
+
 static struct device_attribute net_class_attributes[] = {
 	__ATTR(addr_len, S_IRUGO, show_addr_len, NULL),
 	__ATTR(dev_id, S_IRUGO, show_dev_id, NULL),
+	__ATTR(ifalias, S_IRUGO | S_IWUSR, show_ifalias, store_ifalias),
 	__ATTR(iflink, S_IRUGO, show_iflink, NULL),
 	__ATTR(ifindex, S_IRUGO, show_ifindex, NULL),
 	__ATTR(features, S_IRUGO, show_features, NULL),
@@ -418,6 +453,7 @@ static void netdev_release(struct device *d)
 
 	BUG_ON(dev->reg_state != NETREG_RELEASED);
 
+	kfree(dev->ifalias);
 	kfree((char *)dev - dev->padded);
 }
 

net/core/rtnetlink.c

@@ -586,6 +586,7 @@ static inline size_t if_nlmsg_size(const struct net_device *dev)
 {
 	return NLMSG_ALIGN(sizeof(struct ifinfomsg))
 	       + nla_total_size(IFNAMSIZ) /* IFLA_IFNAME */
+	       + nla_total_size(IFALIASZ) /* IFLA_IFALIAS */
 	       + nla_total_size(IFNAMSIZ) /* IFLA_QDISC */
 	       + nla_total_size(sizeof(struct rtnl_link_ifmap))
 	       + nla_total_size(sizeof(struct rtnl_link_stats))
@@ -640,6 +641,9 @@ static int rtnl_fill_ifinfo(struct sk_buff *skb, struct net_device *dev,
 	if (txq->qdisc_sleeping)
 		NLA_PUT_STRING(skb, IFLA_QDISC, txq->qdisc_sleeping->ops->id);
 
+	if (dev->ifalias)
+		NLA_PUT_STRING(skb, IFLA_IFALIAS, dev->ifalias);
+
 	if (1) {
 		struct rtnl_link_ifmap map = {
 			.mem_start   = dev->mem_start,
@@ -713,6 +717,7 @@ const struct nla_policy ifla_policy[IFLA_MAX+1] = {
 	[IFLA_LINKMODE]		= { .type = NLA_U8 },
 	[IFLA_LINKINFO]		= { .type = NLA_NESTED },
 	[IFLA_NET_NS_PID]	= { .type = NLA_U32 },
+	[IFLA_IFALIAS]	        = { .type = NLA_STRING, .len = IFALIASZ-1 },
 };
 
 static const struct nla_policy ifla_info_policy[IFLA_INFO_MAX+1] = {
@@ -853,6 +858,14 @@ static int do_setlink(struct net_device *dev, struct ifinfomsg *ifm,
 		modified = 1;
 	}
 
+	if (tb[IFLA_IFALIAS]) {
+		err = dev_set_alias(dev, nla_data(tb[IFLA_IFALIAS]),
+				    nla_len(tb[IFLA_IFALIAS]));
+		if (err < 0)
+			goto errout;
+		modified = 1;
+	}
+
 	if (tb[IFLA_BROADCAST]) {
 		nla_memcpy(dev->broadcast, tb[IFLA_BROADCAST], dev->addr_len);
 		send_addr_notify = 1;