linux-kernel - Re: tty: n_gsm: fix closing multiplexer mode

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Date:   Mon, 22 May 2017 19:16:17 +0100
From:   Alan Cox <gnomes@...rguk.ukuu.org.uk>
To:     Sascha Hauer <s.hauer@...gutronix.de>
Cc:     linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>, kernel@...gutronix.de
Subject: Re: tty: n_gsm: fix closing multiplexer mode

> disconnect frame before initialising multiplex mode. Since it's not so
> nice that userspace has to know the layout of a disconnect frame,
> the second patch introduces a disconnect ioctl which can be issued
> right before closing the physical port during the first session.
> This ioctl is only useful when during the second session it is known
> the the first session has been closed properly, so I'm not sure
> how useful it is to introduce such an ioctl.

I don't think it justifies an ioctl and the likely use case is that the
tty is hung up when the process dies so would already be in N_TTY at the
point anyone tried to clean up.

A more interesting question - and I don't have enough hardware to test
this any more - would be whether we can safely send that sequence if our
initial connects failed a few times so we try disconnect/reconnect.

Alan