Commit 7391ee16 authored by Peter Hurley's avatar Peter Hurley Committed by Greg Kroah-Hartman
Browse files

tty: Simplify flip buffer list with 0-sized sentinel 



Use a 0-sized sentinel to avoid assigning the head ptr from
the driver side thread. This also eliminates testing head/tail
for NULL.

When the sentinel is first 'consumed' by the buffer work
(or by tty_buffer_flush()), it is detached from the list but not
freed nor added to the free list. Both buffer work and
tty_buffer_flush() continue to preserve at least 1 flip buffer
to which head & tail is pointed.

Signed-off-by: default avatarPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 809850b7

drivers/tty/tty_buffer.c

+18 −31
Original line number Diff line number Diff line
@@ -49,13 +49,16 @@ void tty_buffer_free_all(struct tty_port *port) 


	while ((p = buf->head) != NULL) {

		buf->head = p->next;

		if (p->size > 0)

			kfree(p);

	}

	llist = llist_del_all(&buf->free);

	llist_for_each_entry_safe(p, next, llist, free)

		kfree(p);



	buf->tail = NULL;

	tty_buffer_reset(&buf->sentinel, 0);

	buf->head = &buf->sentinel;

	buf->tail = &buf->sentinel;

	buf->memory_used = 0;

}
@@ -120,7 +123,7 @@ static void tty_buffer_free(struct tty_port *port, struct tty_buffer *b) 


	if (b->size > MIN_TTYB_SIZE)

		kfree(b);

	else

	else if (b->size > 0)

		llist_add(&b->free, &buf->free);

}
@@ -140,8 +143,6 @@ static void __tty_buffer_flush(struct tty_port *port) 
	struct tty_bufhead *buf = &port->buf;

	struct tty_buffer *next;



	if (unlikely(buf->head == NULL))

		return;

	while ((next = buf->head->next) != NULL) {

		tty_buffer_free(port, buf->head);

		buf->head = next;
@@ -200,23 +201,14 @@ int tty_buffer_request_room(struct tty_port *port, size_t size) 
	int left;

	unsigned long flags;

	spin_lock_irqsave(&buf->lock, flags);

	/* 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 */

	b = buf->tail;

	if (b != NULL)

	left = b->size - b->used;

	else

		left = 0;



	if (left < size) {

		/* This is the slow path - looking for new buffers to use */

		if ((n = tty_buffer_alloc(port, size)) != NULL) {

			if (b != NULL) {

			b->next = n;

			b->commit = b->used;

			} else

				buf->head = n;

			buf->tail = n;

		} else

			size = left;
@@ -247,10 +239,8 @@ int tty_insert_flip_string_fixed_flag(struct tty_port *port, 
		int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);

		int space = tty_buffer_request_room(port, goal);

		struct tty_buffer *tb = port->buf.tail;

		/* If there is no space then tb may be NULL */

		if (unlikely(space == 0)) {

		if (unlikely(space == 0))

			break;

		}

		memcpy(char_buf_ptr(tb, tb->used), chars, space);

		memset(flag_buf_ptr(tb, tb->used), flag, space);

		tb->used += space;
@@ -285,10 +275,8 @@ int tty_insert_flip_string_flags(struct tty_port *port, 
		int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);

		int space = tty_buffer_request_room(port, goal);

		struct tty_buffer *tb = port->buf.tail;

		/* If there is no space then tb may be NULL */

		if (unlikely(space == 0)) {

		if (unlikely(space == 0))

			break;

		}

		memcpy(char_buf_ptr(tb, tb->used), chars, space);

		memcpy(flag_buf_ptr(tb, tb->used), flags, space);

		tb->used += space;
@@ -322,7 +310,6 @@ void tty_schedule_flip(struct tty_port *port) 
	WARN_ON(port->low_latency);



	spin_lock_irqsave(&buf->lock, flags);

	if (buf->tail != NULL)

	buf->tail->commit = buf->tail->used;

	spin_unlock_irqrestore(&buf->lock, flags);

	schedule_work(&buf->work);
@@ -438,8 +425,8 @@ static void flush_to_ldisc(struct work_struct *work) 
	spin_lock_irqsave(&buf->lock, flags);



	if (!test_and_set_bit(TTYP_FLUSHING, &port->iflags)) {

		struct tty_buffer *head;

		while ((head = buf->head) != NULL) {

		while (1) {

			struct tty_buffer *head = buf->head;

			int count;



			count = head->commit - head->read;
@@ -509,7 +496,6 @@ void tty_flip_buffer_push(struct tty_port *port) 
	unsigned long flags;



	spin_lock_irqsave(&buf->lock, flags);

	if (buf->tail != NULL)

	buf->tail->commit = buf->tail->used;

	spin_unlock_irqrestore(&buf->lock, flags);
@@ -535,8 +521,9 @@ void tty_buffer_init(struct tty_port *port) 
	struct tty_bufhead *buf = &port->buf;



	spin_lock_init(&buf->lock);

	buf->head = NULL;

	buf->tail = NULL;

	tty_buffer_reset(&buf->sentinel, 0);

	buf->head = &buf->sentinel;

	buf->tail = &buf->sentinel;

	init_llist_head(&buf->free);

	buf->memory_used = 0;

	INIT_WORK(&buf->work, flush_to_ldisc);

include/linux/tty.h

+1 −0
Original line number Diff line number Diff line
@@ -67,6 +67,7 @@ static inline char *flag_buf_ptr(struct tty_buffer *b, int ofs) 
struct tty_bufhead {

	struct work_struct work;

	spinlock_t lock;

	struct tty_buffer sentinel;

	struct tty_buffer *head;	/* Queue head */

	struct tty_buffer *tail;	/* Active buffer */

	struct llist_head free;		/* Free queue head */

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