Re: [PATCH 1/2] Introduce tty_unregister_ldisc()

[Paul Fulghum <paulkf@microgate.com>]

The following patch would be more appropriate than
my last suggestion for the case of trying to register
a ldisc driver to an occupied slot.

It does not make sense to allow an existing
registered driver to be overwritten, even
if the refcount is zero.

This *should* not happen with unique ldisc numbers,
but it seems like a reasonable check. Even if
Alexey's patch is applied, this would be a
reasonable check to integrate.

-- 
Paul Fulghum
paulkf@microgate.com

--- linux-2.6.11/drivers/char/tty_io.c	2005-03-02 01:38:10.000000000 -0600
+++ b/drivers/char/tty_io.c	2005-06-01 08:34:05.000000000 -0500
@@ -263,10 +263,14 @@ int tty_register_ldisc(int disc, struct 
 	
 	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;
+		if (tty_ldiscs[disc].flags & LDISC_FLAG_DEFINED)
+			ret = -EBUSY;
+		else {
+			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;