From: Cyrill Gorcunov <gorcunov@openvz.org>
To: Alan Cox <alan@lxorguk.ukuu.org.uk>
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
Date: Thu, 13 Sep 2012 20:41:00 +0400 [thread overview]
Message-ID: <20120913164100.GN19956@moon> (raw)
In-Reply-To: <20120913172507.5039e3c6@pyramind.ukuu.org.uk>
On Thu, Sep 13, 2012 at 05:25:07PM +0100, Alan Cox wrote:
> 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?
Yes. Btw, as far as I see the same applies to lock bit on its own. One
process may lock it while another process may unlock it right after that.
> > > 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.
Ah, thanks a lot, Alan, I'll take a look!
Cyrill
next prev parent reply other threads:[~2012-09-13 16:41 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-09-13 9:56 [RFC] tty: Add get- ioctls to fetch tty status Cyrill Gorcunov
2012-09-13 11:46 ` Jiri Slaby
2012-09-13 11:51 ` Cyrill Gorcunov
2012-09-13 12:51 ` Alan Cox
2012-09-13 12:54 ` Cyrill Gorcunov
2012-09-13 16:25 ` Alan Cox
2012-09-13 16:41 ` Cyrill Gorcunov [this message]
2012-09-22 18:06 ` Cyrill Gorcunov
2012-09-22 20:07 ` Greg Kroah-Hartman
2012-09-22 20:11 ` Cyrill Gorcunov
2012-09-22 21:52 ` Cyrill Gorcunov
2012-09-23 1:09 ` Greg Kroah-Hartman
2012-09-23 6:40 ` Cyrill Gorcunov
2012-09-23 14:46 ` H. Peter Anvin
2012-09-23 15:21 ` Cyrill Gorcunov
2012-09-24 14:14 ` Cyrill Gorcunov
2012-09-27 14:05 ` Cyrill Gorcunov
2012-09-27 14:14 ` Alan Cox
2012-09-27 14:14 ` Cyrill Gorcunov
2012-09-27 14:17 ` H. Peter Anvin
2012-09-27 14:21 ` Cyrill Gorcunov
2012-09-27 14:43 ` H. Peter Anvin
2012-09-27 14:48 ` Cyrill Gorcunov
2012-09-27 15:05 ` H. Peter Anvin
2012-09-27 15:13 ` Alan Cox
2012-09-27 15:23 ` Cyrill Gorcunov
2012-09-27 16:00 ` Alan Cox
2012-09-27 16:06 ` Cyrill Gorcunov
2012-09-27 15:47 ` Cyrill Gorcunov
2012-09-22 23:15 ` Alan Cox
2012-09-23 1:43 ` Eric W. Biederman
2012-09-23 6:40 ` Cyrill Gorcunov
2012-09-23 14:44 ` H. Peter Anvin
2012-09-23 15:22 ` Cyrill Gorcunov
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