linux-kernel - Re: TTY: tty

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Message-ID: <4F6F365D.5060703@nod.at>
Date:	Sun, 25 Mar 2012 17:14:37 +0200
From:	Richard Weinberger <richard@....at>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
CC:	Al Viro <viro@...IV.linux.org.uk>, Jiri Slaby <jslaby@...e.cz>,
	linux-kernel@...r.kernel.org, gregkh@...uxfoundation.org,
	Jiri Slaby <jirislaby@...il.com>
Subject: Re: TTY: tty_port questions

Am 25.03.2012 16:51, schrieb Alan Cox:
> On Sat, 24 Mar 2012 23:20:01 +0000
> Al Viro <viro@...IV.linux.org.uk> wrote:
> 
>> On Mon, Mar 12, 2012 at 11:48:32AM +0000, Alan Cox wrote:
>>
>>>>> It will be. In order to fix the tty locking mess we need to shove a lot
>>>>> of stuff whose lifetime is the lifetime of the physical port somewhere
>>>>> else - the tty_port is that structure.
>>>>>
>>>>
>>>> "It will be" in terms of "not now"? ;-)
>>>
>>> As in, it's the very next step on.
>>
>> FWIW, uml console in default config is basically "start xterm for each VC".
>> What do you suggest to do on vhangup() on one of those?
> 
> What posix says must happen. Which is that the running processes get a
> hangup. So a vhangup() would ensure there were no old apps on the UML
> guess talking to the xterm (eg stealing login credentials, or abusing
> TIOCSTI etc).

Looks like Debian's /bin/login is violating POSIX. AFACT it does not
call vhangup() at all.

> The fact it's an xterm isn't really relevant. That's just the physical
> interface and vhangup is about breaking the logical link. The xterm would
> continue, no reason for it to do otherwise I can see ?
> 

As I wrote in my very first mail, if I implement tty_operations->hangup()
a vhangup() closes the current TTY and the shiny new login shell dies because
read/write() returns EIO.

So, the question is whether tty_port is not suitable for consoles or my driver
(see first mail in thread) is broken.

Thanks,
//richard



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