3 files changed, 26 insertions, 14 deletions

diff --git a/Documentation/tty.txt b/Documentation/tty.txt
index 3958cf746dd..8ff7bc2a081 100644
--- a/Documentation/tty.txt
+++ b/Documentation/tty.txt
@@ -22,7 +22,7 @@ copy of the structure. You must not re-register over the top of the line
 discipline even with the same data or your computer again will be eaten by
 demons.
 
-In order to remove a line discipline call tty_register_ldisc passing NULL.
+In order to remove a line discipline call tty_unregister_ldisc().
 In ancient times this always worked. In modern times the function will
 return -EBUSY if the ldisc is currently in use. Since the ldisc referencing
 code manages the module counts this should not usually be a concern.
diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
index 31831030f73..cc4b43bad70 100644
--- a/drivers/char/tty_io.c
+++ b/drivers/char/tty_io.c
@@ -251,7 +251,7 @@ static void tty_set_termios_ldisc(struct tty_struct *tty, int num)
  
 static DEFINE_SPINLOCK(tty_ldisc_lock);
 static DECLARE_WAIT_QUEUE_HEAD(tty_ldisc_wait);
-static struct tty_ldisc tty_ldiscs[NR_LDISCS];  /* line disc dispatch table     */
+static struct tty_ldisc tty_ldiscs[NR_LDISCS];  /* line disc dispatch table */
 
 int tty_register_ldisc(int disc, struct tty_ldisc *new_ldisc)
 {
@@ -262,24 +262,35 @@ int tty_register_ldisc(int disc, struct tty_ldisc *new_ldisc)
                 return -EINVAL;
         
         spin_lock_irqsave(&tty_ldisc_lock, flags);
-        if (new_ldisc) {
-                tty_ldiscs[disc] = *new_ldisc;
-                tty_ldiscs[disc].num = disc;
-                tty_ldiscs[disc].flags |= LDISC_FLAG_DEFINED;
-                tty_ldiscs[disc].refcount = 0;
-        } else {
-                if(tty_ldiscs[disc].refcount)
-                        ret = -EBUSY;
-                else
-                        tty_ldiscs[disc].flags &= ~LDISC_FLAG_DEFINED;
-        }
+        tty_ldiscs[disc] = *new_ldisc;
+        tty_ldiscs[disc].num = disc;
+        tty_ldiscs[disc].flags |= LDISC_FLAG_DEFINED;
+        tty_ldiscs[disc].refcount = 0;
         spin_unlock_irqrestore(&tty_ldisc_lock, flags);
         
         return ret;
 }
-
 EXPORT_SYMBOL(tty_register_ldisc);
 
+int tty_unregister_ldisc(int disc)
+{
+        unsigned long flags;
+        int ret = 0;
+
+        if (disc < N_TTY || disc >= NR_LDISCS)
+                return -EINVAL;
+
+        spin_lock_irqsave(&tty_ldisc_lock, flags);
+        if (tty_ldiscs[disc].refcount)
+                ret = -EBUSY;
+        else
+                tty_ldiscs[disc].flags &= ~LDISC_FLAG_DEFINED;
+        spin_unlock_irqrestore(&tty_ldisc_lock, flags);
+
+        return ret;
+}
+EXPORT_SYMBOL(tty_unregister_ldisc);
+
 struct tty_ldisc *tty_ldisc_get(int disc)
 {
         unsigned long flags;
diff --git a/include/linux/tty.h b/include/linux/tty.h
index 1b76106272d..59ff42c629e 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -345,6 +345,7 @@ extern int tty_check_change(struct tty_struct * tty);
 extern void stop_tty(struct tty_struct * tty);
 extern void start_tty(struct tty_struct * tty);
 extern int tty_register_ldisc(int disc, struct tty_ldisc *new_ldisc);
+extern int tty_unregister_ldisc(int disc);
 extern int tty_register_driver(struct tty_driver *driver);
 extern int tty_unregister_driver(struct tty_driver *driver);
 extern void tty_register_device(struct tty_driver *driver, unsigned index, struct device *dev);