Re: TTY: tty_port questions

[Richard Weinberger]

On 11.03.2012 12:01, Richard Weinberger wrote:
> Am 11.03.2012 00:21, schrieb Richard Weinberger:
> > Am 10.03.2012 23:51, schrieb Jiri Slaby:
> > > On 03/10/2012 11:26 PM, Richard Weinberger wrote:
> > > > Hi!
> > >
> > > > While moving UML's console driver to tty_port some strange things
> > > > happened. So, I have a few questions. :-)
> > >
> > > > The original driver did not implement tty_operations->hangup(). If
> > > > I implement it and call tty_port_hangup(), as Alan suggested, the
> > > > login fails on all TTYs except tty0. It fails because the opened
> > > > TTY returns EIO upon read()/write() after /bin/login called
> > > > vhangup().
> > >
> > > > The call chain is: vhangup() ->  tty_vhangup_self() ->  tty_vhangup()
> > > > ->  __tty_hangup()
> > >
> > > > Within __tty_hangup() something happens that I don't fully
> > > > understand:
> > >
> > > > if (cons_filp) { if (tty->ops->close) for (n = 0; n<  closecount;
> > > > n++) tty->ops->close(tty, cons_filp); } else if (tty->ops->hangup)
> > > > (tty->ops->hangup)(tty);
> > >
> > > > Login on tty0 works because cons_filp is not NULL and
> > > > tty->ops->close() is called. On the other hand login fails on every
> > > > other TTY because cons_filp remains NULL and the TTY hangs up.
> > >
> > > > Is there something missing in my hangup function?
> > >
> > > > If I omit tty_operations->hangup() and leave it, like the old
> > > > driver, NULL non-tty0 TTYs cannot be opened. (getty terminates
> > > > immediately because it cannot open any TTY.) open() retuns -EIO
> > > > because the TTY_CLOSING is set in tty->flags.
> > >
> > > > How can this be?
> > >
> > > Hmm, it looks like some process is sitting on a TTY which was hung.
> > > And the system offers this hung TTY to others on further opens. Could
> > > you check that there is no process with open TTY after the vhangup?
> >
> > "lsof | grep tty" does not show anything else than tty0. :-\
>
> BTW: When I start the kernel with /bin/sh as init, opening and writing to any TTY works fine.
> It looks like Fedora 16's userspace does something that makes the TTYs unhappy.
>
> Thanks,
> //richard

Another question, what is the purpose of tty_port->console?
It seems to have no user.

Is tty_port really the right thing for a console driver like in the UML 
case?

Thanks,
//richard
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