linux-kernel - Re: tty: add 'active' sysfs attribute to tty0 and console device

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Message-ID: <20101116171447.29336514@lxorguk.ukuu.org.uk>
Date:	Tue, 16 Nov 2010 17:14:47 +0000
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Kay Sievers <kay.sievers@...y.org>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	Greg KH <greg@...ah.com>,
	Lennart Poettering <lennart@...ttering.net>,
	Werner Fink <werner@...e.de>, Jiri Slaby <jslaby@...e.cz>
Subject: Re: tty: add 'active' sysfs attribute to tty0 and console device

> > NAK this, its a nonsense interface
> >
> > Seriously what use is an interface that tells you "what the console might
> > have been", this is why we have a proper event tracking interface instead.
> 
> You mean the VT_WAITEVENT? Sleeping ioctls() can't be used. The time
> between the check for the current, and you go to sleep in the ioctl()
> for teh next is a window which isn't covered with such interface.

The only thing you need to add is VT_GETACTIVE, which is fine providing
you know how to use it, but in both cases it is basically useless because
by the time you've asked the question the answer is undefined. You can
only use an interface of this type if you lock against VT changes, which
is how the X interface works if you look at it.

So what are you going to do with the return value from an interface which
provide "what was the console, perhaps, at some point you asked but could
even have been deleted, assigned to a different user, hot unplugged or
moved to another framebuffer device by the time I answer"

What is it for ???

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