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:   Tue, 14 Mar 2017 06:12:47 +0800
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     okash.khawaja@...il.com
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 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.

thanks,

greg k-h