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

From: Greg Kroah-Hartman
Date: Mon Mar 13 2017 - 18:13:15 EST

On Mon, Mar 13, 2017 at 10:05:52PM +0000, okash.khawaja@xxxxxxxxx wrote:
> Allow access to TTY device from kernel. This is based on Alan Cox's patch
> ( at,
> 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@xxxxxxxxx>
> Reviewed-by: Samuel Thibault <samuel.thibault@xxxxxxxxxxxx>

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.


greg k-h