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I'm creating a script for polling information about network interfaces. For this I get some data from /sysfs.

Everything went fine until I wanted to clarify all possible states of an interface (Which are they btw? I'm aware for now only about up, down and unknown). I went through /usr/src/linux/Documentation/sysfs-rules.txt and found this:

Accessing /sys/class/net/eth0/device is a bug in the application

Is there a reason for this? Could someone explain me if I'm doing something wrong by getting information from /sysfs?

I don't iterate through all interfaces in /sysfs but get all network interfaces with getifaddrs(3). Perhaps there is another method to get iface status? Thanks.

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It's the device link in class directories that you aren't supposed to use. The idea is that /sys/class/net/eth0 is a symbolic link to somewhere under /sys/devices, and the device link merely links to a (grand-)*parent directory; instead of using the device link, you're supposed to walk back to a parent directory if needed.

Accessing files in /sys/class/net/eth0/ is fine.

If you're refering to the operational status found in /sys/class/net/eth0/operstate, there are a few more. The names are defined in net/core/net-sysfs.c and the constants in include/uapi/linux/if.h. They come from RFC 2863.

  • Thanks. I figures out about device link after I posted the question already, but still wanted to hear some thoughts about the rest. – UVV Aug 15 '14 at 10:36

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