ethtool: Report link-down while interface is down

While an interface is down, many implementations of
ethtool_ops::get_link, including the default, ethtool_op_get_link(),
will report the last link state seen while the interface was up.  In
general the current physical link state is not available if the
interface is down.

Define ETHTOOL_GLINK to reflect whether the interface *and* any
physical port have a working link, and consistently return 0 when the
interface is down.
Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/ethtool.h

@@ -691,7 +691,9 @@ struct ethtool_ops {
 #define ETHTOOL_GMSGLVL		0x00000007 /* Get driver message level */
 #define ETHTOOL_SMSGLVL		0x00000008 /* Set driver msg level. */
 #define ETHTOOL_NWAY_RST	0x00000009 /* Restart autonegotiation. */
-#define ETHTOOL_GLINK		0x0000000a /* Get link status (ethtool_value) */
+/* Get link status for host, i.e. whether the interface *and* the
+ * physical port (if there is one) are up (ethtool_value). */
+#define ETHTOOL_GLINK		0x0000000a
 #define ETHTOOL_GEEPROM		0x0000000b /* Get EEPROM data */
 #define ETHTOOL_SEEPROM		0x0000000c /* Set EEPROM data. */
 #define ETHTOOL_GCOALESCE	0x0000000e /* Get coalesce config */

net/core/ethtool.c

@@ -891,6 +891,20 @@ static int ethtool_nway_reset(struct net_device *dev)
 	return dev->ethtool_ops->nway_reset(dev);
 }
 
+static int ethtool_get_link(struct net_device *dev, char __user *useraddr)
+{
+	struct ethtool_value edata = { .cmd = ETHTOOL_GLINK };
+
+	if (!dev->ethtool_ops->get_link)
+		return -EOPNOTSUPP;
+
+	edata.data = netif_running(dev) && dev->ethtool_ops->get_link(dev);
+
+	if (copy_to_user(useraddr, &edata, sizeof(edata)))
+		return -EFAULT;
+	return 0;
+}
+
 static int ethtool_get_eeprom(struct net_device *dev, void __user *useraddr)
 {
 	struct ethtool_eeprom eeprom;
@@ -1530,8 +1544,7 @@ int dev_ethtool(struct net *net, struct ifreq *ifr)
 		rc = ethtool_nway_reset(dev);
 		break;
 	case ETHTOOL_GLINK:
-		rc = ethtool_get_value(dev, useraddr, ethcmd,
-				       dev->ethtool_ops->get_link);
+		rc = ethtool_get_link(dev, useraddr);
 		break;
 	case ETHTOOL_GEEPROM:
 		rc = ethtool_get_eeprom(dev, useraddr);