linux-kernel - Re: RFC: mcu_tty: Trying to open /dev/ttyUSB0 and lock access from a kernel driver

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Message-ID: <20170926000516.7b556e58@alans-desktop>
Date:   Tue, 26 Sep 2017 00:05:16 +0100
From:   Alan Cox <gnomes@...rguk.ukuu.org.uk>
To:     Ulf Samuelsson <linux-kernel@...gii.com>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: RFC: mcu_tty: Trying to open /dev/ttyUSB0 and lock access from
 a kernel driver

On Mon, 25 Sep 2017 15:01:13 +0200
Ulf Samuelsson <linux-kernel@...gii.com> wrote:

> Trying to open /dev/ttyUSB from a kernel driver (which works), but 
> locking the
> serial port so noone else can access it does not work.
> Any advice would be appreciated.

File locks are advisory only.

For the rest of it you might want to take a look at how the gsm mux
driver works (the protocol stuff is scary but you can ignore that end).
It plugs a line discipline into a tty and that muxes out as a collection
of ttys and shows how it's meant to be done.

That also means you have an owning process with the port open that can do
locking on it and/or route any raw read/writes to the master port into
the bit bucket.

Alan