Re: [PATCH] Cygwin: pinfo: Align CTTY behavior to the statement of POSIX.

[Takashi Yano <takashi.yano@nifty.ne.jp>]

On Tue, 20 Dec 2022 19:14:35 +0100
Corinna Vinschen wrote:
> Hi Takashi,
> 
> On Dec 20 21:41, Takashi Yano wrote:
> > POSIX states "A terminal may be the controlling terminal for at most
> > one session."
> > https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap11.html
> > 
> > However, in cygwin, multiple sessions could be associated with the
> > same TTY. This patch aligns CTTY behavior to the statement of POSIX.
> > 
> > Signed-off-by: Takashi Yano <takashi.yano@nifty.ne.jp>
> > ---
> >  winsup/cygwin/fhandler/termios.cc | 6 +++++-
> >  winsup/cygwin/mm/cygheap.cc       | 2 ++
> >  winsup/cygwin/pinfo.cc            | 4 +++-
> >  3 files changed, 10 insertions(+), 2 deletions(-)
> 
> Do you want to handle this as bug (3.4) or extension (3.5)?

I think this is bug fix (3.4).

> > diff --git a/winsup/cygwin/pinfo.cc b/winsup/cygwin/pinfo.cc
> > index e086ab9a8..749a4064c 100644
> > --- a/winsup/cygwin/pinfo.cc
> > +++ b/winsup/cygwin/pinfo.cc
> > @@ -528,7 +528,9 @@ _pinfo::set_ctty (fhandler_termios *fh, int flags)
> >  {
> >    tty_min& tc = *fh->tc ();
> >    debug_printf ("old %s, ctty device number %y, tc.ntty device number %y flags & O_NOCTTY %y", __ctty (), ctty, tc.ntty, flags & O_NOCTTY);
> > -  if (fh && (ctty <= 0 || ctty == tc.ntty) && !(flags & O_NOCTTY))
> > +  if (tc.getsid () && tc.getsid () != pid)
> > +    ; /* Do not attach if another session already attached to the CTTY. */
> 
> I'm sure I'm missing something, but I'm a bit puzzled about the
> 
>   tc.getsid () != pid
> 
> test here.  If that's not the case, this process is the process group
> leader and already has a controlling tty, isn't it?

You are right. But, it seems that set_cttt() procedure other
than setting pinfo::ctty and cygpeap->ctty is necessary even
in that case. So, I revised the patch. Please see v2 patch.

-- 
Takashi Yano <takashi.yano@nifty.ne.jp>