Commit 33b37a33 authored by Paul Fulghum's avatar Paul Fulghum Committed by Linus Torvalds
Browse files

[PATCH] remove active field from tty buffer structure 



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: default avatarPaul Fulghum <paulkf@microgate.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 2c3bb20f

drivers/char/tty_io.c

+4 −12
Original line number Diff line number Diff line
@@ -267,7 +267,6 @@ static struct tty_buffer *tty_buffer_alloc(size_t size) 
	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_struct *tty, size_t size) 
	/* 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_struct *tty, size_t size) 
		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 *tty) 
{

	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);

}
@@ -2902,10 +2896,8 @@ void tty_flip_buffer_push(struct tty_struct *tty) 
{

	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)

include/linux/kbd_kern.h

+1 −3
Original line number Diff line number Diff line
@@ -155,10 +155,8 @@ static inline void con_schedule_flip(struct tty_struct *t) 
{

	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);

}

include/linux/tty.h

+0 −1
Original line number Diff line number Diff line
@@ -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 */

include/linux/tty_flip.h

+1 −1
Original line number Diff line number Diff line
@@ -12,7 +12,7 @@ static inline int tty_insert_flip_char(struct tty_struct *tty, 
					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;

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