linux-kernel - Re: [patch 1/7] tty_port: allow a port to be opened with a tty that has no file handle

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Date:   Mon, 13 Mar 2017 22:38:47 +0000
From:   Okash Khawaja <okash.khawaja@...il.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Jiri Slaby <jslaby@...e.com>,
        Samuel Thibault <samuel.thibault@...-lyon.org>,
        linux-kernel@...r.kernel.org, devel@...verdev.osuosl.org,
        Kirk Reiser <kirk@...sers.ca>, speakup@...ux-speakup.org,
        alan@...ux.intel.com, Chris Brannon <chris@...-brannons.com>
Subject: Re: [patch 1/7] tty_port: allow a port to be opened with a tty that
 has no file handle

On Tue, Mar 14, 2017 at 06:12:47AM +0800, Greg Kroah-Hartman wrote:
> On Mon, Mar 13, 2017 at 10:05:52PM +0000, okash.khawaja@...il.com wrote:
> > Allow access to TTY device from kernel. This is based on Alan Cox's patch
> > (http://www.mail-archive.com/linux-kernel at vger.kernel.org/msg1215095.html),
> > with description quoted below.
> > 
> > "tty_port: allow a port to be opened with a tty that has no file handle
> > 
> > Let us create tty objects entirely in kernel space.
> > 
> > With this a kernel created non file backed tty object could be used to handle
> > data, and set terminal modes. Not all ldiscs can cope with this as N_TTY in
> > particular has to work back to the fs/tty layer.
> > 
> > The tty_port code is however otherwise clean of file handles as far as I can
> > tell as is the low level tty port write path used by the ldisc, the
> > configuration low level interfaces and most of the ldiscs.
> > 
> > Currently you don't have any exposure to see tty hangups because those are
> > built around the file layer. However a) it's a fixed port so you probably
> > don't care about that b) if you do we can add a callback and c) you almost
> > certainly don't want the userspace tear down/rebuild behaviour anyway.
> > 
> > This should however be sufficient if we wanted for example to enumerate all
> > the bluetooth bound fixed ports via ACPI and make them directly available.
> > 
> > It doesn't deal with the case of a user opening a port that's also kernel
> > opened and that would need some locking out (so it returned EBUSY if bound
> > to a kernel device of some kind). That needs resolving along with how you
> > "up" or "down" your new bluetooth device, or enumerate it while providing
> > the existing tty API to avoid regressions (and to debug)."
> > 
> > Signed-off-by: Okash Khawaja <okash.khawaja@...il.com>
> > 
> > Reviewed-by: Samuel Thibault <samuel.thibault@...-lyon.org>
> 
> You do know this is already in 4.11-rc1, right?  Please rebase your
> patch set on 4.11-rc2 at the least and resend.

Didn't realise that! Will resend