hv_netvsc: propogate Hyper-V friendly name into interface alias

This patch implement the 'Device Naming' feature of the Hyper-V
network device API. In Hyper-V on the host through the GUI or PowerShell
it is possible to enable the device naming feature which causes
the host to make available to the guest the name of the device.
This shows up in the RNDIS protocol as the friendly name.

The name has no particular meaning and is limited to 256 characters.
The value can only be set via PowerShell on the host, but could
be scripted for mass deployments. The default value is the
string 'Network Adapter' and since that is the same for all devices
and useless, the driver ignores it.

In Windows, the value goes into a registry key for use in SNMP
ifAlias. For Linux, this patch puts the value in the network
device alias property; where it is visible in ip tools and SNMP.

The host provided ifAlias is just a suggestion, and can be
overridden by later ip commands.

Also requires exporting dev_set_alias in netdev core.

Signed-off-by: Stephen Hemminger <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/net/hyperv/rndis_filter.c

···
 #include <linux/nls.h>
 #include <linux/vmalloc.h>
 #include <linux/rtnetlink.h>
+#include <linux/ucs2_string.h>
 
 #include "hyperv_net.h"
 #include "netvsc_trace.h"
···
 	return ret;
 }
 
+static void rndis_get_friendly_name(struct net_device *net,
+				    struct rndis_device *rndis_device,
+				    struct netvsc_device *net_device)
+{
+	ucs2_char_t wname[256];
+	unsigned long len;
+	u8 ifalias[256];
+	u32 size;
+
+	size = sizeof(wname);
+	if (rndis_filter_query_device(rndis_device, net_device,
+				      RNDIS_OID_GEN_FRIENDLY_NAME,
+				      wname, &size) != 0)
+		return;
+
+	/* Convert Windows Unicode string to UTF-8 */
+	len = ucs2_as_utf8(ifalias, wname, sizeof(ifalias));
+
+	/* ignore the default value from host */
+	if (strcmp(ifalias, "Network Adapter") != 0)
+		dev_set_alias(net, ifalias, len);
+}
+
 struct netvsc_device *rndis_filter_device_add(struct hv_device *dev,
 				      struct netvsc_device_info *device_info)
 {
···
 		goto err_dev_remv;
 
 	memcpy(device_info->mac_adr, rndis_device->hw_mac_adr, ETH_ALEN);
+
+	/* Get friendly name as ifalias*/
+	if (!net->ifalias)
+		rndis_get_friendly_name(net, rndis_device, net_device);
 
 	/* Query and set hardware capabilities */
 	ret = rndis_netdev_set_hwcaps(rndis_device, net_device);

net/core/dev.c

···
 
 	return len;
 }
+EXPORT_SYMBOL(dev_set_alias);
 
 /**
  *	dev_get_alias - get ifalias of a device