From: Paul Fulghum <paulkf@microgate.com>

Remove 'active' field from tty buffer structure.  This was added in 2.6.16
as part of a patch to make the new tty buffering SMP safe.  This field is
unnecessary with the more intelligently written flush_to_ldisc that adds
receive_room handling.

Removing this field reverts to simpler logic where the tail buffer is
always the 'active' buffer, which should not be freed by flush_to_ldisc. 
(active == buffer being filled with new data)

The result is simpler, smaller, and faster tty buffer code.

Signed-off-by: Paul Fulghum <paulkf@microgate.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---

 drivers/char/tty_io.c    |   16 ++++------------
 include/linux/kbd_kern.h |    4 +---
 include/linux/tty.h      |    1 -
 include/linux/tty_flip.h |    2 +-
 4 files changed, 6 insertions(+), 17 deletions(-)

diff -puN drivers/char/tty_io.c~remove-active-field-from-tty-buffer-structure drivers/char/tty_io.c
--- a/drivers/char/tty_io.c~remove-active-field-from-tty-buffer-structure
+++ a/drivers/char/tty_io.c
@@ -267,7 +267,6 @@ static struct tty_buffer *tty_buffer_all
 	p->used = 0;
 	p->size = size;
 	p->next = NULL;
-	p->active = 0;
 	p->commit = 0;
 	p->read = 0;
 	p->char_buf_ptr = (char *)(p->data);
@@ -327,10 +326,9 @@ int tty_buffer_request_room(struct tty_s
 	/* OPTIMISATION: We could keep a per tty "zero" sized buffer to
 	   remove this conditional if its worth it. This would be invisible
 	   to the callers */
-	if ((b = tty->buf.tail) != NULL) {
+	if ((b = tty->buf.tail) != NULL)
 		left = b->size - b->used;
-		b->active = 1;
-	} else
+	else
 		left = 0;
 
 	if (left < size) {
@@ -338,12 +336,10 @@ int tty_buffer_request_room(struct tty_s
 		if ((n = tty_buffer_find(tty, size)) != NULL) {
 			if (b != NULL) {
 				b->next = n;
-				b->active = 0;
 				b->commit = b->used;
 			} else
 				tty->buf.head = n;
 			tty->buf.tail = n;
-			n->active = 1;
 		} else
 			size = left;
 	}
@@ -404,10 +400,8 @@ void tty_schedule_flip(struct tty_struct
 {
 	unsigned long flags;
 	spin_lock_irqsave(&tty->buf.lock, flags);
-	if (tty->buf.tail != NULL) {
-		tty->buf.tail->active = 0;
+	if (tty->buf.tail != NULL)
 		tty->buf.tail->commit = tty->buf.tail->used;
-	}
 	spin_unlock_irqrestore(&tty->buf.lock, flags);
 	schedule_delayed_work(&tty->buf.work, 1);
 }
@@ -2903,10 +2897,8 @@ void tty_flip_buffer_push(struct tty_str
 {
 	unsigned long flags;
 	spin_lock_irqsave(&tty->buf.lock, flags);
-	if (tty->buf.tail != NULL) {
-		tty->buf.tail->active = 0;
+	if (tty->buf.tail != NULL)
 		tty->buf.tail->commit = tty->buf.tail->used;
-	}
 	spin_unlock_irqrestore(&tty->buf.lock, flags);
 
 	if (tty->low_latency)
diff -puN include/linux/kbd_kern.h~remove-active-field-from-tty-buffer-structure include/linux/kbd_kern.h
--- a/include/linux/kbd_kern.h~remove-active-field-from-tty-buffer-structure
+++ a/include/linux/kbd_kern.h
@@ -155,10 +155,8 @@ static inline void con_schedule_flip(str
 {
 	unsigned long flags;
 	spin_lock_irqsave(&t->buf.lock, flags);
-	if (t->buf.tail != NULL) {
-		t->buf.tail->active = 0;
+	if (t->buf.tail != NULL)
 		t->buf.tail->commit = t->buf.tail->used;
-	}
 	spin_unlock_irqrestore(&t->buf.lock, flags);
 	schedule_work(&t->buf.work);
 }
diff -puN include/linux/tty_flip.h~remove-active-field-from-tty-buffer-structure include/linux/tty_flip.h
--- a/include/linux/tty_flip.h~remove-active-field-from-tty-buffer-structure
+++ a/include/linux/tty_flip.h
@@ -12,7 +12,7 @@ static inline int tty_insert_flip_char(s
 					unsigned char ch, char flag)
 {
 	struct tty_buffer *tb = tty->buf.tail;
-	if (tb && tb->active && tb->used < tb->size) {
+	if (tb && tb->used < tb->size) {
 		tb->flag_buf_ptr[tb->used] = flag;
 		tb->char_buf_ptr[tb->used++] = ch;
 		return 1;
diff -puN include/linux/tty.h~remove-active-field-from-tty-buffer-structure include/linux/tty.h
--- a/include/linux/tty.h~remove-active-field-from-tty-buffer-structure
+++ a/include/linux/tty.h
@@ -57,7 +57,6 @@ struct tty_buffer {
 	unsigned char *flag_buf_ptr;
 	int used;
 	int size;
-	int active;
 	int commit;
 	int read;
 	/* Data points here */
_