[patch 1/8] tty_port: allow a port to be opened with a tty that has no file handle

[Samuel Thibault]

okash.khawaja at gmail.com, on dim. 12 mars 2017 12:16:45 +0000, 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 at gmail.com>

When you receive a

Reviewed-by: Samuel Thibault <samuel.thibault at ens-lyon.org>

do include it in your patch, so that when you re-send the series, it has
it already for people to know that it has been reviewed.

Samuel