void tty_ldisc_release(struct tty_struct *tty, struct tty_struct *o_tty)
{
/*
* Prevent flush_to_ldisc() from rescheduling the work for later. Then
* kill any delayed work. As this is the final close it does not
* race with the set_ldisc code path.
*/
tty_lock_pair(tty, o_tty);
tty_ldisc_halt(tty);
tty_ldisc_flush_works(tty);
if (o_tty) {
tty_ldisc_halt(o_tty);
tty_ldisc_flush_works(o_tty);
}
/* This will need doing differently if we need to lock */
tty_ldisc_kill(tty);
if (o_tty)
tty_ldisc_kill(o_tty);
tty_unlock_pair(tty, o_tty);
/* And the memory resources remaining (buffers, termios) will be
disposed of when the kref hits zero */
}
void tty_ldisc_release(struct tty_struct *tty, struct tty_struct *o_tty)
{
/*
* Prevent flush_to_ldisc() from rescheduling the work for later. Then
* kill any delayed work. As this is the final close it does not
* race with the set_ldisc code path.
*/
tty_unlock();
tty_ldisc_halt(tty);
tty_ldisc_flush_works(tty);
tty_lock();
mutex_lock(&tty->ldisc_mutex);
/*
* Now kill off the ldisc
*/
tty_ldisc_close(tty, tty->ldisc);
tty_ldisc_put(tty->ldisc);
/* Force an oops if we mess this up */
tty->ldisc = NULL;
/* Ensure the next open requests the N_TTY ldisc */
tty_set_termios_ldisc(tty, N_TTY);
mutex_unlock(&tty->ldisc_mutex);
/* This will need doing differently if we need to lock */
if (o_tty)
tty_ldisc_release(o_tty, NULL);
/* And the memory resources remaining (buffers, termios) will be
disposed of when the kref hits zero */
}
int tty_set_ldisc(struct tty_struct *tty, int ldisc)
{
int retval;
struct tty_ldisc *o_ldisc, *new_ldisc;
int work, o_work = 0;
struct tty_struct *o_tty;
new_ldisc = tty_ldisc_get(ldisc);
if (IS_ERR(new_ldisc))
return PTR_ERR(new_ldisc);
tty_lock();
/*
* We need to look at the tty locking here for pty/tty pairs
* when both sides try to change in parallel.
*/
o_tty = tty->link; /* o_tty is the pty side or NULL */
/*
* Check the no-op case
*/
if (tty->ldisc->ops->num == ldisc) {
tty_unlock();
tty_ldisc_put(new_ldisc);
return 0;
}
tty_unlock();
/*
* Problem: What do we do if this blocks ?
* We could deadlock here
*/
tty_wait_until_sent(tty, 0);
tty_lock();
mutex_lock(&tty->ldisc_mutex);
/*
* We could be midstream of another ldisc change which has
* dropped the lock during processing. If so we need to wait.
*/
while (test_bit(TTY_LDISC_CHANGING, &tty->flags)) {
mutex_unlock(&tty->ldisc_mutex);
tty_unlock();
wait_event(tty_ldisc_wait,
test_bit(TTY_LDISC_CHANGING, &tty->flags) == 0);
tty_lock();
mutex_lock(&tty->ldisc_mutex);
}
set_bit(TTY_LDISC_CHANGING, &tty->flags);
/*
* No more input please, we are switching. The new ldisc
* will update this value in the ldisc open function
*/
tty->receive_room = 0;
o_ldisc = tty->ldisc;
tty_unlock();
/*
* Make sure we don't change while someone holds a
* reference to the line discipline. The TTY_LDISC bit
* prevents anyone taking a reference once it is clear.
* We need the lock to avoid racing reference takers.
*
* We must clear the TTY_LDISC bit here to avoid a livelock
* with a userspace app continually trying to use the tty in
* parallel to the change and re-referencing the tty.
*/
work = tty_ldisc_halt(tty);
if (o_tty)
o_work = tty_ldisc_halt(o_tty);
/*
* Wait for ->hangup_work and ->buf.work handlers to terminate.
* We must drop the mutex here in case a hangup is also in process.
*/
mutex_unlock(&tty->ldisc_mutex);
tty_ldisc_flush_works(tty);
retval = tty_ldisc_wait_idle(tty);
tty_lock();
mutex_lock(&tty->ldisc_mutex);
/* handle wait idle failure locked */
if (retval) {
tty_ldisc_put(new_ldisc);
goto enable;
}
if (test_bit(TTY_HUPPED, &tty->flags)) {
/* We were raced by the hangup method. It will have stomped
the ldisc data and closed the ldisc down */
clear_bit(TTY_LDISC_CHANGING, &tty->flags);
mutex_unlock(&tty->ldisc_mutex);
tty_ldisc_put(new_ldisc);
tty_unlock();
return -EIO;
}
/* Shutdown the current discipline. */
tty_ldisc_close(tty, o_ldisc);
/* Now set up the new line discipline. */
tty_ldisc_assign(tty, new_ldisc);
tty_set_termios_ldisc(tty, ldisc);
retval = tty_ldisc_open(tty, new_ldisc);
if (retval < 0) {
/* Back to the old one or N_TTY if we can't */
tty_ldisc_put(new_ldisc);
tty_ldisc_restore(tty, o_ldisc);
}
/* At this point we hold a reference to the new ldisc and a
a reference to the old ldisc. If we ended up flipping back
to the existing ldisc we have two references to it */
if (tty->ldisc->ops->num != o_ldisc->ops->num && tty->ops->set_ldisc)
tty->ops->set_ldisc(tty);
tty_ldisc_put(o_ldisc);
enable:
/*
* Allow ldisc referencing to occur again
*/
tty_ldisc_enable(tty);
if (o_tty)
tty_ldisc_enable(o_tty);
/* Restart the work queue in case no characters kick it off. Safe if
already running */
if (work)
schedule_work(&tty->buf.work);
if (o_work)
schedule_work(&o_tty->buf.work);
mutex_unlock(&tty->ldisc_mutex);
tty_unlock();
return retval;
}
