Messages in this thread | | | Date | Thu, 13 Sep 2012 20:41:00 +0400 | From | Cyrill Gorcunov <> | Subject | Re: [RFC] tty: Add get- ioctls to fetch tty status |
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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
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