Re: [PATCH] net-sysfs: Report link speed as signed integer

Jiri Pirko [off-list ref] writes:

Mon, Jun 02, 2014 at 04:25:15PM CEST, mprivozn@redhat.com wrote:

quoted

The link speed is available at /sys/class/net/$nic/speed.
However, the speed is printed in unsigned integer format. This
makes userspace applications read an incorrect value (which
moreover changes through several architectures) while in fact
'-1' should be reported.

Before the change:
 # cat /sys/class/net/eth0/speed
 4294967295

After the change:
 # cat /sys/class/net/eth0/speed
 -1

Signed-off-by: Michal Privoznik <redacted>
---
net/core/net-sysfs.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
index 1cac29e..99afdea 100644
--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c

@@ -173,7 +173,7 @@ static ssize_t speed_show(struct device *dev,

	if (netif_running(netdev)) {
		struct ethtool_cmd cmd;
		if (!__ethtool_get_settings(netdev, &cmd))
-			ret = sprintf(buf, fmt_udec, ethtool_cmd_speed(&cmd));
+			ret = sprintf(buf, fmt_dec, ethtool_cmd_speed(&cmd));

I wonder why this should be signed. What -1 means? What driver reports
this?

I believe many drivers will do this when the speed is unknown, e.g
because the link is down.  For example:

bjorn@nemi:~$ grep . /sys/class/net/eth0/speed
4294967295
bjorn@nemi:~$ ls -l /sys/class/net/eth0/device/driver
lrwxrwxrwx 1 root root 0 Jun  2 10:48 /sys/class/net/eth0/device/driver -> ../../../bus/pci/drivers/e1000e
bjorn@nemi:~$ ethtool eth0
Settings for eth0:
        Supported ports: [ TP ]
        Supported link modes:   10baseT/Half 10baseT/Full 
                                100baseT/Half 100baseT/Full 
                                1000baseT/Full 
        Supported pause frame use: No
        Supports auto-negotiation: Yes
        Advertised link modes:  10baseT/Half 10baseT/Full 
                                100baseT/Half 100baseT/Full 
                                1000baseT/Full 
        Advertised pause frame use: No
        Advertised auto-negotiation: Yes
        Speed: Unknown!
        Duplex: Unknown! (255)
        Port: Twisted Pair
        PHYAD: 2
        Transceiver: internal
        Auto-negotiation: on
        MDI-X: Unknown
Cannot get wake-on-lan settings: Operation not permitted
        Current message level: 0x00000007 (7)
                               drv probe link
        Link detected: no



Bjørn