[PATCH/RFC] New module refcounting for TTY ldisc

[Max Krasnyansky]

Folks,

Here is the patch that converts TTY ldisc code to the new 
module refcounting API.
Tested with Bluetooth UART driver and seemed to work fine.
Other ldiscs are not affected because their ldisc->owner is
set to NULL.

If people are ok with it I'll push it to my BK tree along with
fixed Bluetooth ldisc.

# This is a BitKeeper generated patch for the following project:
# Project Name: Linux kernel tree
# This patch format is intended for GNU patch command version 2.5 or higher.
# This patch includes the following deltas:
#	           ChangeSet	1.889   -> 1.890  
#	drivers/char/tty_io.c	1.50    -> 1.51   
#	include/linux/tty_ldisc.h	1.2     -> 1.3    
#
# The following is the BitKeeper ChangeSet Log
# --------------------------------------------
# 02/12/23	[e-mail]	1.890
# New module refcounting for TTY ldisc
# --------------------------------------------
#
diff -Nru a/drivers/char/tty_io.c b/drivers/char/tty_io.c
--- a/drivers/char/tty_io.c	Wed Dec 25 19:49:53 2002
+++ b/drivers/char/tty_io.c	Wed Dec 25 19:49:53 2002
@@ -292,6 +292,10 @@
 
 	if (tty->ldisc.num == ldisc)
 		return 0;	/* We are already in the desired discipline */
+
+	if (!try_module_get(ldiscs[ldisc].owner))
+	       	return -EINVAL;
+	
 	o_ldisc = tty->ldisc;
 
 	tty_wait_until_sent(tty, 0);
@@ -306,9 +310,13 @@
 	if (tty->ldisc.open)
 		retval = (tty->ldisc.open)(tty);
 	if (retval < 0) {
+		module_put(tty->ldisc.owner);
+		
 		tty->ldisc = o_ldisc;
 		tty->termios->c_line = tty->ldisc.num;
 		if (tty->ldisc.open && (tty->ldisc.open(tty) < 0)) {
+			module_put(tty->ldisc.owner);
+
 			tty->ldisc = ldiscs[N_TTY];
 			tty->termios->c_line = N_TTY;
 			if (tty->ldisc.open) {
@@ -320,7 +328,10 @@
 					      tty_name(tty, buf), r);
 			}
 		}
+	} else {
+		module_put(o_ldisc.owner);
 	}
+	
 	if (tty->ldisc.num != o_ldisc.num && tty->driver.set_ldisc)
 		tty->driver.set_ldisc(tty);
 	return retval;
@@ -489,6 +500,8 @@
 	if (tty->ldisc.num != ldiscs[N_TTY].num) {
 		if (tty->ldisc.close)
 			(tty->ldisc.close)(tty);
+		module_put(tty->ldisc.owner);
+		
 		tty->ldisc = ldiscs[N_TTY];
 		tty->termios->c_line = N_TTY;
 		if (tty->ldisc.open) {
@@ -1259,6 +1272,8 @@
 	 */
 	if (tty->ldisc.close)
 		(tty->ldisc.close)(tty);
+	module_put(tty->ldisc.owner);
+	
 	tty->ldisc = ldiscs[N_TTY];
 	tty->termios->c_line = N_TTY;
 	if (o_tty) {
diff -Nru a/include/linux/tty_ldisc.h b/include/linux/tty_ldisc.h
--- a/include/linux/tty_ldisc.h	Wed Dec 25 19:49:53 2002
+++ b/include/linux/tty_ldisc.h	Wed Dec 25 19:49:53 2002
@@ -105,6 +105,7 @@
 	char	*name;
 	int	num;
 	int	flags;
+	
 	/*
 	 * The following routines are called from above.
 	 */
@@ -129,6 +130,8 @@
 			       char *fp, int count);
 	int	(*receive_room)(struct tty_struct *);
 	void	(*write_wakeup)(struct tty_struct *);
+
+	struct  module *owner;
 };
 
 #define TTY_LDISC_MAGIC	0x5403

--

Max