[PATCH] net: network device name ifalias support

[PATCH] net: network device name ifalias support

[Stephen Hemminger]

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>

---
Note: this is not IP alias which is something completely different.


--- a/include/linux/if.h	2008-09-22 11:54:10.000000000 -0700
+++ b/include/linux/if.h	2008-09-22 16:22:24.000000000 -0700
@@ -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). */
--- a/include/linux/if_link.h	2008-09-22 11:50:28.000000000 -0700
+++ b/include/linux/if_link.h	2008-09-22 11:54:32.000000000 -0700
@@ -79,6 +79,7 @@ enum
 	IFLA_LINKINFO,
 #define IFLA_LINKINFO IFLA_LINKINFO
 	IFLA_NET_NS_PID,
+	IFLA_IFALIAS,
 	__IFLA_MAX
 };
 
--- a/include/linux/netdevice.h	2008-09-22 11:46:10.000000000 -0700
+++ b/include/linux/netdevice.h	2008-09-22 16:04:24.000000000 -0700
@@ -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,
 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);
--- a/net/core/dev.c	2008-09-22 11:58:17.000000000 -0700
+++ b/net/core/dev.c	2008-09-22 17:26:57.000000000 -0700
@@ -954,6 +954,29 @@ rollback:
 }
 
 /**
+ *	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
  *
--- a/net/core/net-sysfs.c	2008-09-22 12:03:34.000000000 -0700
+++ b/net/core/net-sysfs.c	2008-09-22 17:27:14.000000000 -0700
@@ -209,9 +209,44 @@ static ssize_t store_tx_queue_len(struct
 	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
 
 	BUG_ON(dev->reg_state != NETREG_RELEASED);
 
+	kfree(dev->ifalias);
 	kfree((char *)dev - dev->padded);
 }
 
--- a/net/core/rtnetlink.c	2008-09-22 11:48:30.000000000 -0700
+++ b/net/core/rtnetlink.c	2008-09-22 16:23:56.000000000 -0700
@@ -586,6 +586,7 @@ static inline size_t if_nlmsg_size(const
 {
 	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_bu
 	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
 	[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 
 		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;

Re: [PATCH] net: network device name ifalias support

[David Miller]

From: Stephen Hemminger <shemminger@vyatta.com>
Date: Mon, 22 Sep 2008 17:43:46 -0700

> +	dev->ifalias = krealloc(dev->ifalias, len+1, GFP_KERNEL);
> +	if (!dev->ifalias)
> +		return -ENOMEM;
> +
> +	strlcpy(dev->ifalias, alias, len+1);
> +	return len;

It might be cleaner to use kstrdup() and free the old pointer, if
any, here.

	char *new = kstrdup(alias, GFP_KERNEL);
	if (!new)
		return -ENOMEM;
	kfree(dev->ifalias);
	dev->ifalias = new;
	return len;

That way all of this "len+1" stuff goes away.

Re: [PATCH] net: network device name ifalias support

[Stephen Hemminger]

On Mon, 22 Sep 2008 19:44:23 -0700 (PDT)
David Miller <davem@davemloft.net> wrote:

> From: Stephen Hemminger <shemminger@vyatta.com>
> Date: Mon, 22 Sep 2008 17:43:46 -0700
> 
> > +	dev->ifalias = krealloc(dev->ifalias, len+1, GFP_KERNEL);
> > +	if (!dev->ifalias)
> > +		return -ENOMEM;
> > +
> > +	strlcpy(dev->ifalias, alias, len+1);
> > +	return len;
> 
> It might be cleaner to use kstrdup() and free the old pointer, if
> any, here.
> 
> 	char *new = kstrdup(alias, GFP_KERNEL);
> 	if (!new)
> 		return -ENOMEM;
> 	kfree(dev->ifalias);
> 	dev->ifalias = new;
> 	return len;
> 
> That way all of this "len+1" stuff goes away.

Won't work because input string is not necessarily null-terminated.
In the sysfs case we want there is a trailing newline, and this
way avoids copying once there and then copying again.

Re: [PATCH] net: network device name ifalias support

[David Miller]

From: Stephen Hemminger <shemminger@vyatta.com>
Date: Mon, 22 Sep 2008 20:47:18 -0700

> On Mon, 22 Sep 2008 19:44:23 -0700 (PDT)
> David Miller <davem@davemloft.net> wrote:
> 
> > It might be cleaner to use kstrdup() and free the old pointer, if
> > any, here.
> > 
> > 	char *new = kstrdup(alias, GFP_KERNEL);
> > 	if (!new)
> > 		return -ENOMEM;
> > 	kfree(dev->ifalias);
> > 	dev->ifalias = new;
> > 	return len;
> > 
> > That way all of this "len+1" stuff goes away.
> 
> Won't work because input string is not necessarily null-terminated.
> In the sysfs case we want there is a trailing newline, and this
> way avoids copying once there and then copying again.

Ok, fair enough.  I've applied your original patch to net-next-2.6,
thanks!

[PATCH net-next]: net: remove ifalias on empty given alias

[Oliver Hartkopp]

[-- Attachment #1: Type: text/plain, Size: 430 bytes --]

This patch removes the potentially allocated ifalias when the (new) 
given alias is empty.

E.g. when setting

echo "" > /sys/class/net/eth0/ifalias

Signed-off-by: Oliver Hartkopp <oliver@hartkopp.net>
---

Hello Stephen,

this patch allows to 'remove' or reset the ifalias by giving an empty alias.
The patch is tested.
Btw. ifalias is a nice idea also for CAN bus people to 'name' a given 
CAN bus.

Thanks & regards,
Oliver



[-- Attachment #2: empty_ifalias.patch --]
[-- Type: text/x-patch, Size: 466 bytes --]

diff --git a/net/core/dev.c b/net/core/dev.c
index e913905..a90737f 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -967,6 +967,14 @@ int dev_set_alias(struct net_device *dev, const char *alias, size_t len)
 	if (len >= IFALIASZ)
 		return -EINVAL;
 
+	if (!len) {
+		if (dev->ifalias) {
+			kfree(dev->ifalias);
+			dev->ifalias = NULL;
+		}
+		return 0;
+	}
+
 	dev->ifalias = krealloc(dev->ifalias, len+1, GFP_KERNEL);
 	if (!dev->ifalias)
 		return -ENOMEM;

Re: [PATCH net-next]: net: remove ifalias on empty given alias

[Stephen Hemminger]

On Tue, 23 Sep 2008 21:52:08 +0200
Oliver Hartkopp <oliver@hartkopp.net> wrote:

> This patch removes the potentially allocated ifalias when the (new) 
> given alias is empty.
> 
> E.g. when setting
> 
> echo "" > /sys/class/net/eth0/ifalias
> 
> Signed-off-by: Oliver Hartkopp <oliver@hartkopp.net>
> ---
> 
> Hello Stephen,
> 
> this patch allows to 'remove' or reset the ifalias by giving an empty alias.
> The patch is tested.
> Btw. ifalias is a nice idea also for CAN bus people to 'name' a given 
> CAN bus.
> 
> Thanks & regards,
> Oliver
> 
> 

Acked-by: Stephen Hemminger <shemminger@vyatta.com>

Also, udev could put a default value in based on the slot information it has.

Re: [PATCH net-next]: net: remove ifalias on empty given alias

[David Miller]

From: Stephen Hemminger <shemminger@vyatta.com>
Date: Tue, 23 Sep 2008 13:14:52 -0700

> On Tue, 23 Sep 2008 21:52:08 +0200
> Oliver Hartkopp <oliver@hartkopp.net> wrote:
> 
> > This patch removes the potentially allocated ifalias when the (new) 
> > given alias is empty.
> > 
> > E.g. when setting
> > 
> > echo "" > /sys/class/net/eth0/ifalias
> > 
> > Signed-off-by: Oliver Hartkopp <oliver@hartkopp.net>
> > ---
> > 
> > Hello Stephen,
> > 
> > this patch allows to 'remove' or reset the ifalias by giving an empty alias.
> > The patch is tested.
> > Btw. ifalias is a nice idea also for CAN bus people to 'name' a given 
> > CAN bus.
> > 
> > Thanks & regards,
> > Oliver
> > 
> > 
> 
> Acked-by: Stephen Hemminger <shemminger@vyatta.com>
> 
> Also, udev could put a default value in based on the slot information it has.

I've applied Oliver's patch.