netdev - Re: cross namespace interface notification for tun devices

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Message-ID: <CAHmME9pACTes07b3=JKgh8GOCOX4w64EwxrGmGbSRGQtssNHMQ@mail.gmail.com>
Date:   Tue, 19 Sep 2017 03:24:05 +0200
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Netdev <netdev@...r.kernel.org>
Cc:     Mathias <mathias@...l-andersen.dk>
Subject: Re: cross namespace interface notification for tun devices

On Mon, Sep 18, 2017 at 8:47 PM, Jason A. Donenfeld <Jason@...c4.com> 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.

View attachment "tuntest.c" of type "text/x-csrc" (1373 bytes)