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Date: Thu, 13 Sep 2012 17:25:07 +0100
From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: LKML <linux-kernel@vger.kernel.org>, "H. Peter Anvin" <hpa@zytor.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Pavel Emelyanov <xemul@parallels.com>
Subject: Re: [RFC] tty: Add get- ioctls to fetch tty status
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On Thu, 13 Sep 2012 16:54:01 +0400
Cyrill Gorcunov <gorcunov@openvz.org> wrote:

> On Thu, Sep 13, 2012 at 01:51:31PM +0100, Alan Cox wrote:
> > > +static int pty_get_lock(struct tty_struct *tty, int __user *arg)
> > > +{
> > > +	int locked = test_bit(TTY_PTY_LOCK, &tty->flags);
> > > +	if (put_user(locked, arg))
> > > +		return -EFAULT;
> > 
> > Now explain exactly how this doesn't race with another thread chanigng
> > the lock setting ?
> 
> It's the same as to set/clear this bit, isn't it? Please correct me
> if I'm wrong.

So by the time you've finished the test bit and returned it to user space
the answer may have changed ?

> > The other comment I have is that it might be better put these in now
> > there are sysfs patches for the tty layer bouncing about to provide the
> > needed infrastructure ?
> 
> Alan, could you please point me where these patches are living, so I would
> take a look and check them out

linux-serial or check tty-next as I think Greg has now merged the test
patch.