linux-kernel - Re: [PATCH] net-sysfs: Report link speed only when possible

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Date:	Fri, 6 Jun 2014 10:57:33 +0200
From:	Jiri Pirko <jiri@...nulli.us>
To:	Michal Privoznik <mprivozn@...hat.com>
Cc:	davem@...emloft.net, gregkh@...uxfoundation.org,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH] net-sysfs: Report link speed only when possible

Fri, Jun 06, 2014 at 10:40:30AM CEST, mprivozn@...hat.com wrote:
>The link speed is available at /sys/class/net/$nic/speed.
>However, in some cases, depending on the driver, if the link is
>not plugged, -1 is reported (this is the case of e1000e for
>instance). To make things worse, the value is printed out as an

Actually, SPEED_UNKNOWN is also -1
So e1000e is not any exception.


>unsigned integer, so you'll get this shady number which you can't
>evaluate correctly. This is actually a regression in 3.X kernels
>as the commit that broke things is 8ae6daca. With this change,
>you'll get -EINVAL whenever a -1 is to be printed out.
>
>Before the change:
>  # cat /sys/class/net/eth0/speed
>  4294967295
>
>After the change:
>  # cat /sys/class/net/eth0/speed
>  cat: /sys/class/net/eth0/speed: Invalid argument
>
>Signed-off-by: Michal Privoznik <mprivozn@...hat.com>
>---
> net/core/net-sysfs.c | 9 +++++++--
> 1 file changed, 7 insertions(+), 2 deletions(-)
>
>diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
>index 1cac29e..ce4b298 100644
>--- a/net/core/net-sysfs.c
>+++ b/net/core/net-sysfs.c
>@@ -172,8 +172,13 @@ 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));
>+		if (!__ethtool_get_settings(netdev, &cmd)) {
>+			__u32 speed = ethtool_cmd_speed(&cmd);
>+
>+			if (speed != (__u32) -1)

Just rather use SPEED_UNKNOWN instead of -1 here.


>+				ret = sprintf(buf, fmt_udec,
>+					      ethtool_cmd_speed(&cmd));
>+		}
> 	}
> 	rtnl_unlock();
> 	return ret;
>-- 
>2.0.0
>
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