[patch 1/6] tty_port: allow a port to be opened with a tty that has no file handle

[John Covici]

I wonder if applications should be allowed to open the tty?  What if
you had a speech dispatcher serial driver or some such?

On Sat, 25 Feb 2017 20:05:43 -0500,
Samuel Thibault wrote:
> 
> Samuel Thibault, on dim. 26 févr. 2017 01:53:42 +0100, wrote:
> > Okash Khawaja, on sam. 25 févr. 2017 19:21:32 +0000, wrote:
> > > Allow access to TTY device from kernel.
> > 
> > When opening the TTY from an application (e.g. echo foo > /dev/ttyS0),
> > we get this:
> > 
> > ttyS ttyS0: tty_open: tty->count(3) != #fd's(2)
> > ttyS ttyS0: tty_release: tty->count(3) != #fd's(2)
> > 
> > This is because the number of files in tty_files doesn't match the
> > open count for tty. spk_ttyio_initialise_ldisc should thus mimic
> > tty_open a bit more: after calling tty_open_by_driver, it should call
> > tty_add_file(tty, NULL); to add an entry in the tty_files list (and why
> > not calling check_tty_count too).  And of course, the converse
> > (tty_del_file) should be called by spk_ttyio_release between the
> > tty_ldisc_flush call and tty_unlock.
> 
> Oops, of course you don't have a filp to give to tty_del_file, so that
> can't work. Ok, let's ignore the issue for now, applications are not
> supposed to open the tty used by speakup anyway (and would get an EIO
> error anyway).
> 
> Samuel
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         John Covici
         covici at ccs.covici.com