/**
* tty_ldisc_change - change line discipline
* @tty: tty to change
* @disc: new line discipine number
*
* Change the line discipline of the tty. The tty must have an old
* ldisc attached to, we must handle it properly. Sandix implement
* it quite simple, but please look at linux, see how complex it is!
* XXX tty shoud be locked
*/
int tty_ldisc_change(struct tty_struct *tty, int disc)
{
int ret;
struct tty_ldisc *old_ldisc, *new_ldisc;
BUG_ON(!tty->ldisc);
if (tty->ldisc->ops->num == disc)
return 0;
tty_lock(tty);
new_ldisc = tty_ldisc_get(tty, disc);
if (IS_ERR(new_ldisc)) {
tty_unlock(tty);
return PTR_ERR(new_ldisc);
}
old_ldisc = tty->ldisc;
/* Close the old one */
tty_ldisc_close(tty, old_ldisc);
/* Set up the new one */
tty->ldisc = new_ldisc;
tty_set_termios_ldisc(tty, disc);
ret = tty_ldisc_open(tty, new_ldisc);
if (ret) {
/* Back to the old one or N_TTY */
tty_ldisc_put(new_ldisc);
tty_ldisc_restore(tty, old_ldisc);
}
/*
* At this point we hold a reference to the new ldisc and a
* reference to the old ldisc, or we hold two references to
* the old ldisc (if it was restored as part of error cleanup
* above). In either case, releasing a single reference from
* the old ldisc is correct.
*/
tty_ldisc_put(old_ldisc);
tty_unlock(tty);
return ret;
}
int tty_set_ldisc(struct tty_struct *tty, int ldisc)
{
int retval;
struct tty_ldisc o_ldisc, new_ldisc;
int work;
unsigned long flags;
struct tty_struct *o_tty;
restart:
/* This is a bit ugly for now but means we can break the 'ldisc
is part of the tty struct' assumption later */
retval = tty_ldisc_get(ldisc, &new_ldisc);
if (retval)
return retval;
/*
* Problem: What do we do if this blocks ?
*/
tty_wait_until_sent(tty, 0);
if (tty->ldisc.ops->num == ldisc) {
tty_ldisc_put(new_ldisc.ops);
return 0;
}
/*
* 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;
o_tty = tty->link;
/*
* 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.
*/
clear_bit(TTY_LDISC, &tty->flags);
if (o_tty)
clear_bit(TTY_LDISC, &o_tty->flags);
spin_lock_irqsave(&tty_ldisc_lock, flags);
if (tty->ldisc.refcount || (o_tty && o_tty->ldisc.refcount)) {
if (tty->ldisc.refcount) {
/* Free the new ldisc we grabbed. Must drop the lock
first. */
spin_unlock_irqrestore(&tty_ldisc_lock, flags);
tty_ldisc_put(new_ldisc.ops);
/*
* There are several reasons we may be busy, including
* random momentary I/O traffic. We must therefore
* retry. We could distinguish between blocking ops
* and retries if we made tty_ldisc_wait() smarter.
* That is up for discussion.
*/
if (wait_event_interruptible(tty_ldisc_wait, tty->ldisc.refcount == 0) < 0)
return -ERESTARTSYS;
goto restart;
}
if (o_tty && o_tty->ldisc.refcount) {
spin_unlock_irqrestore(&tty_ldisc_lock, flags);
tty_ldisc_put(o_tty->ldisc.ops);
if (wait_event_interruptible(tty_ldisc_wait, o_tty->ldisc.refcount == 0) < 0)
return -ERESTARTSYS;
goto restart;
}
}
/*
* If the TTY_LDISC bit is set, then we are racing against
* another ldisc change
*/
if (test_bit(TTY_LDISC_CHANGING, &tty->flags)) {
struct tty_ldisc *ld;
spin_unlock_irqrestore(&tty_ldisc_lock, flags);
tty_ldisc_put(new_ldisc.ops);
ld = tty_ldisc_ref_wait(tty);
tty_ldisc_deref(ld);
goto restart;
}
/*
* This flag is used to avoid two parallel ldisc changes. Once
* open and close are fine grained locked this may work better
* as a mutex shared with the open/close/hup paths
*/
set_bit(TTY_LDISC_CHANGING, &tty->flags);
if (o_tty)
set_bit(TTY_LDISC_CHANGING, &o_tty->flags);
spin_unlock_irqrestore(&tty_ldisc_lock, flags);
/*
* From this point on we know nobody has an ldisc
* usage reference, nor can they obtain one until
* we say so later on.
*/
work = cancel_delayed_work(&tty->buf.work);
/*
* Wait for ->hangup_work and ->buf.work handlers to terminate
* MUST NOT hold locks here.
*/
flush_scheduled_work();
/* Shutdown the current discipline. */
if (o_ldisc.ops->close)
(o_ldisc.ops->close)(tty);
/* Now set up the new line discipline. */
tty_ldisc_assign(tty, &new_ldisc);
tty_set_termios_ldisc(tty, ldisc);
if (new_ldisc.ops->open)
retval = (new_ldisc.ops->open)(tty);
if (retval < 0) {
tty_ldisc_put(new_ldisc.ops);
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.ops);
/*
* Allow ldisc referencing to occur as soon as the driver
* ldisc callback completes.
*/
tty_ldisc_enable(tty);
if (o_tty)
tty_ldisc_enable(o_tty);
/* Restart it in case no characters kick it off. Safe if
already running */
if (work)
schedule_delayed_work(&tty->buf.work, 1);
return retval;
}
int tty_set_ldisc(struct tty_struct *tty, int ldisc)
{
int retval;
struct tty_ldisc *old_ldisc, *new_ldisc;
struct tty_struct *o_tty = tty->link;
new_ldisc = tty_ldisc_get(tty, ldisc);
if (IS_ERR(new_ldisc))
return PTR_ERR(new_ldisc);
retval = tty_ldisc_lock_pair_timeout(tty, o_tty, 5 * HZ);
if (retval) {
tty_ldisc_put(new_ldisc);
return retval;
}
/*
* Check the no-op case
*/
if (tty->ldisc->ops->num == ldisc) {
tty_ldisc_enable_pair(tty, o_tty);
tty_ldisc_put(new_ldisc);
return 0;
}
old_ldisc = tty->ldisc;
tty_lock(tty);
if (test_bit(TTY_HUPPING, &tty->flags) ||
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 */
tty_ldisc_enable_pair(tty, o_tty);
tty_ldisc_put(new_ldisc);
tty_unlock(tty);
return -EIO;
}
/* Shutdown the old discipline. */
tty_ldisc_close(tty, old_ldisc);
/* Now set up the new line discipline. */
tty->ldisc = 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, old_ldisc);
}
if (tty->ldisc->ops->num != old_ldisc->ops->num && tty->ops->set_ldisc)
tty->ops->set_ldisc(tty);
/* At this point we hold a reference to the new ldisc and a
reference to the old ldisc, or we hold two references to
the old ldisc (if it was restored as part of error cleanup
above). In either case, releasing a single reference from
the old ldisc is correct. */
tty_ldisc_put(old_ldisc);
/*
* Allow ldisc referencing to occur again
*/
tty_ldisc_enable_pair(tty, o_tty);
/* Restart the work queue in case no characters kick it off. Safe if
already running */
schedule_work(&tty->port->buf.work);
if (o_tty)
schedule_work(&o_tty->port->buf.work);
tty_unlock(tty);
return retval;
}
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);
/*
* 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_ldisc_put(new_ldisc);
return 0;
}
/*
* Problem: What do we do if this blocks ?
* We could deadlock here
*/
tty_wait_until_sent(tty, 0);
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);
wait_event(tty_ldisc_wait,
test_bit(TTY_LDISC_CHANGING, &tty->flags) == 0);
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;
/*
* 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);
flush_scheduled_work();
mutex_lock(&tty->ldisc_mutex);
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);
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);
/*
* 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_delayed_work(&tty->buf.work, 1);
if (o_work)
schedule_delayed_work(&o_tty->buf.work, 1);
mutex_unlock(&tty->ldisc_mutex);
return retval;
}
int tty_set_ldisc(struct tty_struct *tty, int ldisc)
{
int retval;
struct tty_ldisc *o_ldisc, *new_ldisc;
struct tty_struct *o_tty = tty->link;
new_ldisc = tty_ldisc_get(tty, ldisc);
if (IS_ERR(new_ldisc))
return PTR_ERR(new_ldisc);
retval = tty_ldisc_lock_pair_timeout(tty, o_tty, 5 * HZ);
if (retval) {
tty_ldisc_put(new_ldisc);
return retval;
}
/*
* Check the no-op case
*/
if (tty->ldisc->ops->num == ldisc) {
tty_ldisc_enable_pair(tty, o_tty);
tty_ldisc_put(new_ldisc);
return 0;
}
/* FIXME: why 'shutoff' input if the ldisc is locked? */
tty->receive_room = 0;
o_ldisc = tty->ldisc;
tty_lock(tty);
/* FIXME: for testing only */
WARN_ON(test_bit(TTY_HUPPED, &tty->flags));
if (test_bit(TTY_HUPPING, &tty->flags)) {
/* We were raced by the hangup method. It will have stomped
the ldisc data and closed the ldisc down */
tty_ldisc_enable_pair(tty, o_tty);
tty_ldisc_put(new_ldisc);
tty_unlock(tty);
return -EIO;
}
/* Shutdown the current discipline. */
tty_ldisc_close(tty, o_ldisc);
/* Now set up the new line discipline. */
tty->ldisc = 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);
/*
* Allow ldisc referencing to occur again
*/
tty_ldisc_enable_pair(tty, o_tty);
/* Restart the work queue in case no characters kick it off. Safe if
already running */
schedule_work(&tty->port->buf.work);
if (o_tty)
schedule_work(&o_tty->port->buf.work);
tty_unlock(tty);
return retval;
}
