[PATCH net-next] net-sysfs: restore behavior for not running devices

[Eric Dumazet <edumazet@google.com>]

modprobe dummy dumdummies=1

Old behavior :

$ cat /sys/class/net/dummy0/carrier
cat: /sys/class/net/dummy0/carrier: Invalid argument

After blamed commit, an empty string is reported.

$ cat /sys/class/net/dummy0/carrier
$

In this commit, I restore the old behavior for carrier,
speed and duplex attributes.

Fixes: 79c61899b5ee ("net-sysfs: remove rtnl_trylock from device attributes")
Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 net/core/net-sysfs.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
index 3fe2c521e5740436687f09c572754c5d071038f4..f61c1d829811941671981a395fc4cbc57cf48d23 100644
--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c
@@ -313,12 +313,13 @@ static ssize_t carrier_show(struct device *dev,
 			    struct device_attribute *attr, char *buf)
 {
 	struct net_device *netdev = to_net_dev(dev);
-	int ret = -EINVAL;
+	int ret;
 
 	ret = sysfs_rtnl_lock(&dev->kobj, &attr->attr, netdev);
 	if (ret)
 		return ret;
 
+	ret = -EINVAL;
 	if (netif_running(netdev)) {
 		/* Synchronize carrier state with link watch,
 		 * see also rtnl_getlink().
@@ -349,6 +350,7 @@ static ssize_t speed_show(struct device *dev,
 	if (ret)
 		return ret;
 
+	ret = -EINVAL;
 	if (netif_running(netdev)) {
 		struct ethtool_link_ksettings cmd;
 
@@ -376,6 +378,7 @@ static ssize_t duplex_show(struct device *dev,
 	if (ret)
 		return ret;
 
+	ret = -EINVAL;
 	if (netif_running(netdev)) {
 		struct ethtool_link_ksettings cmd;
 
-- 
2.48.1.601.g30ceb7b040-goog