linux-kernel - Re: [RFC] tty: Add get- ioctls to fetch tty status

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Message-ID: <5064600D.1090506@zytor.com>
Date:	Thu, 27 Sep 2012 07:17:49 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Cyrill Gorcunov <gorcunov@...nvz.org>
CC:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Pavel Emelyanov <xemul@...allels.com>,
	Jiri Slaby <jslaby@...e.cz>
Subject: Re: [RFC] tty: Add get- ioctls to fetch tty status

On 09/27/2012 07:14 AM, Cyrill Gorcunov wrote:
> On Thu, Sep 27, 2012 at 03:14:47PM +0100, Alan Cox wrote:
>>> Alan, Greg, what's opinion? This flags fetching is the same as say fetching
>>> of termios settings, once fetched they can be changed immediately, and it's
>>> up to caller what to do with termios settings. No?
>>
>> I think you need to explain what you expect to be doing with it, and why
>> it is safe in that application.
>
> OK, it seems it was unclear from changelog. We need to know this parameters
> to be able to restore tty connection after checkpoint.
>
> While we easily can fetch termios settings and such, there are few bits which
> are missed to expord. So this patch provides them to user-space.
>

What bothers me (and the same applies to termios) is that you have NO 
idea if your particular process is the "owner" of that tty.  tty users 
use out-of-band protocols, often implicit, to determine which process 
"owns" the tty state.

If you can't guarantee that ALL those processes are stopped and 
checkpointed/restarted, you have a huge problem.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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