Re: [patch] staging: speakup: safely close tty

From: Okash Khawaja
Date: Tue Jul 11 2017 - 06:39:26 EST


On Mon, Jul 10, 2017 at 12:55:44PM +0100, Alan Cox wrote:
> On Fri, 7 Jul 2017 20:13:01 +0100
> Okash Khawaja <okash.khawaja@xxxxxxxxx> wrote:
> > Speakup opens tty using tty_open_by_driver. When closing, it calls
> > tty_ldisc_release but doesn't close and remove the tty itself. As a
> > result, that tty cannot then be opened from user space. This patch calls
> > tty_release_struct which ensures that tty is safely removed and freed
> > up. It also calls tty_ldisc_release, so speakup doesn't need to call it.
> >
> > This patch also unregisters N_SPEAKUP. It is registered when a speakup
> > module is loaded.
> What happens if after you register it someone assigns that ldisc to
> another tty as well ?
> You should register the ldisc when the relevant module is initialized and
> release it only when the module is unloaded. That way the module ref
> counts will handle cases where someone uses the ldisc with something else.
Sorry if I misunderstood it. That's what we do here.
spk_ttyio_initialise_ldisc is called separately for each module (e.g.
speakup_apollo, speakup_ltlk etc) when it is loaded. spk_ttyio_release
is also called separately for each module when it is unloaded. The ldisc
stays around until the last of the modules is unloaded.

> I'd also btw strongly recommend putting the ldisc and the speakup tty
> driver as different modules.
Sure, that makes sense. I will do that following these patches.