Re: cross namespace interface notification for tun devices

On Mon, Sep 18, 2017 at 8:47 PM, Jason A. Donenfeld [off-list ref] wrote:

The best I've come up with is, in a sleep loop, writing to the tun
device's fd something with a NULL or invalid payload. If the interface
is down, the kernel returns -EIO. If the interface is up, the kernel
returns -EINVAL. This seems to be a reliable distinguisher, but is a
pretty insane way of doing it. And sleep loops are somewhat different
from events too.

Specifically, I'm referring to the horrific hack exemplified in the
attached .c file, in case anybody is curious about the details of what
I'd rather not use.