// SPDX-License-Identifier: GPL-2.0

  /*
   * Tty buffer allocation management
   */
  
  #include <linux/types.h>
  #include <linux/errno.h>
  #include <linux/tty.h>
  #include <linux/tty_driver.h>
  #include <linux/tty_flip.h>
  #include <linux/timer.h>
  #include <linux/string.h>
  #include <linux/slab.h>
  #include <linux/sched.h>

  #include <linux/wait.h>
  #include <linux/bitops.h>
  #include <linux/delay.h>
  #include <linux/module.h>

  #include <linux/ratelimit.h>

  
  #define MIN_TTYB_SIZE	256
  #define TTYB_ALIGN_MASK	255

  /*
   * Byte threshold to limit memory consumption for flip buffers.
   * The actual memory limit is > 2x this amount.
   */

  #define TTYB_DEFAULT_MEM_LIMIT	(640 * 1024UL)

  /*
   * We default to dicing tty buffer allocations to this many characters
   * in order to avoid multiple page allocations. We know the size of
   * tty_buffer itself but it must also be taken into account that the
   * the buffer is 256 byte aligned. See tty_buffer_find for the allocation
   * logic this must match
   */
  
  #define TTY_BUFFER_PAGE	(((PAGE_SIZE - sizeof(struct tty_buffer)) / 2) & ~0xFF)

  /**

   *	tty_buffer_lock_exclusive	-	gain exclusive access to buffer
   *	tty_buffer_unlock_exclusive	-	release exclusive access
   *

   *	@port: tty port owning the flip buffer

   *
   *	Guarantees safe use of the line discipline's receive_buf() method by
   *	excluding the buffer work and any pending flush from using the flip
   *	buffer. Data can continue to be added concurrently to the flip buffer
   *	from the driver side.
   *
   *	On release, the buffer work is restarted if there is data in the
   *	flip buffer
   */
  
  void tty_buffer_lock_exclusive(struct tty_port *port)
  {
  	struct tty_bufhead *buf = &port->buf;
  
  	atomic_inc(&buf->priority);
  	mutex_lock(&buf->lock);
  }

  EXPORT_SYMBOL_GPL(tty_buffer_lock_exclusive);

  
  void tty_buffer_unlock_exclusive(struct tty_port *port)
  {
  	struct tty_bufhead *buf = &port->buf;
  	int restart;
  
  	restart = buf->head->commit != buf->head->read;
  
  	atomic_dec(&buf->priority);
  	mutex_unlock(&buf->lock);
  	if (restart)
  		queue_work(system_unbound_wq, &buf->work);
  }

  EXPORT_SYMBOL_GPL(tty_buffer_unlock_exclusive);

  
  /**

   *	tty_buffer_space_avail	-	return unused buffer space

   *	@port: tty port owning the flip buffer

   *
   *	Returns the # of bytes which can be written by the driver without
   *	reaching the buffer limit.
   *
   *	Note: this does not guarantee that memory is available to write
   *	the returned # of bytes (use tty_prepare_flip_string_xxx() to
   *	pre-allocate if memory guarantee is required).
   */
  
  int tty_buffer_space_avail(struct tty_port *port)
  {

  	int space = port->buf.mem_limit - atomic_read(&port->buf.mem_used);

  	return max(space, 0);
  }

  EXPORT_SYMBOL_GPL(tty_buffer_space_avail);

  static void tty_buffer_reset(struct tty_buffer *p, size_t size)
  {
  	p->used = 0;
  	p->size = size;
  	p->next = NULL;
  	p->commit = 0;
  	p->read = 0;

  	p->flags = 0;

  }

  /**
   *	tty_buffer_free_all		-	free buffers used by a tty

   *	@port: tty port to free from

   *
   *	Remove all the buffers pending on a tty whether queued with data
   *	or in the free ring. Must be called when the tty is no longer in use

   */

  void tty_buffer_free_all(struct tty_port *port)

  {

  	struct tty_bufhead *buf = &port->buf;

  	struct tty_buffer *p, *next;
  	struct llist_node *llist;

  	unsigned int freed = 0;
  	int still_used;

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

  		freed += p->size;

  		if (p->size > 0)
  			kfree(p);

  	}

  	llist = llist_del_all(&buf->free);
  	llist_for_each_entry_safe(p, next, llist, free)

  		kfree(p);

  	tty_buffer_reset(&buf->sentinel, 0);
  	buf->head = &buf->sentinel;
  	buf->tail = &buf->sentinel;

  	still_used = atomic_xchg(&buf->mem_used, 0);
  	WARN(still_used != freed, "we still have not freed %d bytes!",
  			still_used - freed);

  }
  
  /**
   *	tty_buffer_alloc	-	allocate a tty buffer

   *	@port: tty port

   *	@size: desired size (characters)
   *
   *	Allocate a new tty buffer to hold the desired number of characters.

   *	We round our buffers off in 256 character chunks to get better
   *	allocation behaviour.

   *	Return NULL if out of memory or the allocation would exceed the
   *	per device queue

   */

  static struct tty_buffer *tty_buffer_alloc(struct tty_port *port, size_t size)

  {

  	struct llist_node *free;

  	struct tty_buffer *p;

  	/* Round the buffer size out */
  	size = __ALIGN_MASK(size, TTYB_ALIGN_MASK);
  
  	if (size <= MIN_TTYB_SIZE) {

  		free = llist_del_first(&port->buf.free);
  		if (free) {
  			p = llist_entry(free, struct tty_buffer, free);

  			goto found;
  		}
  	}
  
  	/* Should possibly check if this fails for the largest buffer we
  	   have queued and recycle that ? */

  	if (atomic_read(&port->buf.mem_used) > port->buf.mem_limit)

  		return NULL;
  	p = kmalloc(sizeof(struct tty_buffer) + 2 * size, GFP_ATOMIC);
  	if (p == NULL)
  		return NULL;

  found:

  	tty_buffer_reset(p, size);

  	atomic_add(size, &port->buf.mem_used);

  	return p;
  }
  
  /**
   *	tty_buffer_free		-	free a tty buffer

   *	@port: tty port owning the buffer

   *	@b: the buffer to free
   *
   *	Free a tty buffer, or add it to the free list according to our
   *	internal strategy

   */

  static void tty_buffer_free(struct tty_port *port, struct tty_buffer *b)

  {

  	struct tty_bufhead *buf = &port->buf;

  	/* Dumb strategy for now - should keep some stats */

  	WARN_ON(atomic_sub_return(b->size, &buf->mem_used) < 0);

  	if (b->size > MIN_TTYB_SIZE)

  		kfree(b);

  	else if (b->size > 0)

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

  }
  
  /**

   *	tty_buffer_flush		-	flush full tty buffers
   *	@tty: tty to flush

   *	@ld:  optional ldisc ptr (must be referenced)

   *

   *	flush all the buffers containing receive data. If ld != NULL,
   *	flush the ldisc input buffer.

   *

   *	Locking: takes buffer lock to ensure single-threaded flip buffer

   *		 'consumer'

   */

  void tty_buffer_flush(struct tty_struct *tty, struct tty_ldisc *ld)

  {

  	struct tty_port *port = tty->port;

  	struct tty_bufhead *buf = &port->buf;

  	struct tty_buffer *next;

  	atomic_inc(&buf->priority);

  	mutex_lock(&buf->lock);

  	/* paired w/ release in __tty_buffer_request_room; ensures there are
  	 * no pending memory accesses to the freed buffer
  	 */
  	while ((next = smp_load_acquire(&buf->head->next)) != NULL) {

  		tty_buffer_free(port, buf->head);
  		buf->head = next;
  	}
  	buf->head->read = buf->head->commit;

  
  	if (ld && ld->ops->flush_buffer)
  		ld->ops->flush_buffer(tty);

  	atomic_dec(&buf->priority);
  	mutex_unlock(&buf->lock);

  }
  
  /**

   *	tty_buffer_request_room		-	grow tty buffer if needed

   *	@port: tty port

   *	@size: size desired

   *	@flags: buffer flags if new buffer allocated (default = 0)

   *
   *	Make at least size bytes of linear space available for the tty
   *	buffer. If we fail return the size we managed to find.

   *
   *	Will change over to a new buffer if the current buffer is encoded as
   *	TTY_NORMAL (so has no flags buffer) and the new buffer requires
   *	a flags buffer.

   */

  static int __tty_buffer_request_room(struct tty_port *port, size_t size,
  				     int flags)

  {

  	struct tty_bufhead *buf = &port->buf;

  	struct tty_buffer *b, *n;

  	int left, change;

  	b = buf->tail;

  	if (b->flags & TTYB_NORMAL)
  		left = 2 * b->size - b->used;
  	else
  		left = b->size - b->used;

  	change = (b->flags & TTYB_NORMAL) && (~flags & TTYB_NORMAL);
  	if (change || left < size) {

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

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

  			n->flags = flags;

  			buf->tail = n;

  			/* paired w/ acquire in flush_to_ldisc(); ensures
  			 * flush_to_ldisc() sees buffer data.
  			 */
  			smp_store_release(&b->commit, b->used);

  			/* paired w/ acquire in flush_to_ldisc(); ensures the

  			 * latest commit value can be read before the head is
  			 * advanced to the next buffer
  			 */

  			smp_store_release(&b->next, n);

  		} else if (change)
  			size = 0;
  		else

  			size = left;
  	}

  	return size;
  }

  
  int tty_buffer_request_room(struct tty_port *port, size_t size)
  {
  	return __tty_buffer_request_room(port, size, 0);
  }

  EXPORT_SYMBOL_GPL(tty_buffer_request_room);
  
  /**

   *	tty_insert_flip_string_fixed_flag - Add characters to the tty buffer

   *	@port: tty port

   *	@chars: characters

   *	@flag: flag value for each character

   *	@size: size
   *
   *	Queue a series of bytes to the tty buffering. All the characters

   *	passed are marked with the supplied flag. Returns the number added.

   */

  int tty_insert_flip_string_fixed_flag(struct tty_port *port,

  		const unsigned char *chars, char flag, size_t size)

  {
  	int copied = 0;
  	do {

  		int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);

  		int flags = (flag == TTY_NORMAL) ? TTYB_NORMAL : 0;
  		int space = __tty_buffer_request_room(port, goal, flags);

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

  		if (unlikely(space == 0))

  			break;

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

  		if (~tb->flags & TTYB_NORMAL)
  			memset(flag_buf_ptr(tb, tb->used), flag, space);

  		tb->used += space;
  		copied += space;
  		chars += space;
  		/* There is a small chance that we need to split the data over
  		   several buffers. If this is the case we must loop */
  	} while (unlikely(size > copied));
  	return copied;
  }

  EXPORT_SYMBOL(tty_insert_flip_string_fixed_flag);

  
  /**
   *	tty_insert_flip_string_flags	-	Add characters to the tty buffer

   *	@port: tty port

   *	@chars: characters
   *	@flags: flag bytes
   *	@size: size
   *
   *	Queue a series of bytes to the tty buffering. For each character
   *	the flags array indicates the status of the character. Returns the
   *	number added.

   */

  int tty_insert_flip_string_flags(struct tty_port *port,

  		const unsigned char *chars, const char *flags, size_t size)
  {
  	int copied = 0;
  	do {

  		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 (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;
  		copied += space;
  		chars += space;
  		flags += space;
  		/* There is a small chance that we need to split the data over
  		   several buffers. If this is the case we must loop */
  	} while (unlikely(size > copied));
  	return copied;
  }
  EXPORT_SYMBOL(tty_insert_flip_string_flags);
  
  /**

   *	__tty_insert_flip_char   -	Add one character to the tty buffer
   *	@port: tty port
   *	@ch: character
   *	@flag: flag byte
   *
   *	Queue a single byte to the tty buffering, with an optional flag.
   *	This is the slow path of tty_insert_flip_char.
   */
  int __tty_insert_flip_char(struct tty_port *port, unsigned char ch, char flag)
  {

  	struct tty_buffer *tb;

  	int flags = (flag == TTY_NORMAL) ? TTYB_NORMAL : 0;

  	if (!__tty_buffer_request_room(port, 1, flags))

  		return 0;

  	tb = port->buf.tail;

  	if (~tb->flags & TTYB_NORMAL)
  		*flag_buf_ptr(tb, tb->used) = flag;

  	*char_buf_ptr(tb, tb->used++) = ch;
  
  	return 1;
  }
  EXPORT_SYMBOL(__tty_insert_flip_char);
  
  /**

   *	tty_schedule_flip	-	push characters to ldisc

   *	@port: tty port to push from

   *
   *	Takes any pending buffers and transfers their ownership to the
   *	ldisc side of the queue. It then schedules those characters for
   *	processing by the line discipline.

   */

  void tty_schedule_flip(struct tty_port *port)

  {

  	struct tty_bufhead *buf = &port->buf;

  	/* paired w/ acquire in flush_to_ldisc(); ensures
  	 * flush_to_ldisc() sees buffer data.
  	 */
  	smp_store_release(&buf->tail->commit, buf->tail->used);

  	queue_work(system_unbound_wq, &buf->work);

  }
  EXPORT_SYMBOL(tty_schedule_flip);
  
  /**
   *	tty_prepare_flip_string		-	make room for characters

   *	@port: tty port

   *	@chars: return pointer for character write area
   *	@size: desired size
   *
   *	Prepare a block of space in the buffer for data. Returns the length
   *	available and buffer pointer to the space which is now allocated and
   *	accounted for as ready for normal characters. This is used for drivers
   *	that need their own block copy routines into the buffer. There is no
   *	guarantee the buffer is a DMA target!

   */

  int tty_prepare_flip_string(struct tty_port *port, unsigned char **chars,

  		size_t size)

  {

  	int space = __tty_buffer_request_room(port, size, TTYB_NORMAL);

  	if (likely(space)) {

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

  		*chars = char_buf_ptr(tb, tb->used);

  		if (~tb->flags & TTYB_NORMAL)
  			memset(flag_buf_ptr(tb, tb->used), TTY_NORMAL, space);

  		tb->used += space;
  	}
  	return space;
  }
  EXPORT_SYMBOL_GPL(tty_prepare_flip_string);

  /**
   *	tty_ldisc_receive_buf		-	forward data to line discipline
   *	@ld:	line discipline to process input
   *	@p:	char buffer
   *	@f:	TTY_* flags buffer
   *	@count:	number of bytes to process
   *
   *	Callers other than flush_to_ldisc() need to exclude the kworker
   *	from concurrent use of the line discipline, see paste_selection().
   *

   *	Returns the number of bytes processed

   */

  int tty_ldisc_receive_buf(struct tty_ldisc *ld, const unsigned char *p,

  			  char *f, int count)
  {
  	if (ld->ops->receive_buf2)
  		count = ld->ops->receive_buf2(ld->tty, p, f, count);
  	else {
  		count = min_t(int, count, ld->tty->receive_room);
  		if (count && ld->ops->receive_buf)
  			ld->ops->receive_buf(ld->tty, p, f, count);
  	}
  	return count;
  }
  EXPORT_SYMBOL_GPL(tty_ldisc_receive_buf);

  static int

  receive_buf(struct tty_port *port, struct tty_buffer *head, int count)

  {

  	unsigned char *p = char_buf_ptr(head, head->read);

  	char	      *f = NULL;

  	int n;

  
  	if (~head->flags & TTYB_NORMAL)
  		f = flag_buf_ptr(head, head->read);

  	n = port->client_ops->receive_buf(port, p, f, count);
  	if (n > 0)
  		memset(p, 0, n);
  	return n;

  }

  
  /**
   *	flush_to_ldisc
   *	@work: tty structure passed from work queue.
   *
   *	This routine is called out of the software interrupt to flush data
   *	from the buffer chain to the line discipline.
   *

   *	The receive_buf method is single threaded for each tty instance.
   *

   *	Locking: takes buffer lock to ensure single-threaded flip buffer

   *		 'consumer'

   */
  
  static void flush_to_ldisc(struct work_struct *work)
  {

  	struct tty_port *port = container_of(work, struct tty_port, buf.work);
  	struct tty_bufhead *buf = &port->buf;

  	mutex_lock(&buf->lock);

  	while (1) {
  		struct tty_buffer *head = buf->head;

  		struct tty_buffer *next;

  		int count;

  		/* Ldisc or user is trying to gain exclusive access */
  		if (atomic_read(&buf->priority))

  			break;

  		/* paired w/ release in __tty_buffer_request_room();

  		 * ensures commit value read is not stale if the head
  		 * is advancing to the next buffer
  		 */

  		next = smp_load_acquire(&head->next);

  		/* paired w/ release in __tty_buffer_request_room() or in
  		 * tty_buffer_flush(); ensures we see the committed buffer data
  		 */
  		count = smp_load_acquire(&head->commit) - head->read;

  		if (!count) {

  			if (next == NULL)

  				break;

  			buf->head = next;

  			tty_buffer_free(port, head);
  			continue;

  		}

  		count = receive_buf(port, head, count);

  		if (!count)
  			break;

  		head->read += count;

  	}

  	mutex_unlock(&buf->lock);

  }
  
  /**
   *	tty_flip_buffer_push	-	terminal

   *	@port: tty port to push

   *

   *	Queue a push of the terminal flip buffers to the line discipline.
   *	Can be called from IRQ/atomic context.

   *
   *	In the event of the queue being busy for flipping the work will be
   *	held off and retried later.

   */

  void tty_flip_buffer_push(struct tty_port *port)

  {

  	tty_schedule_flip(port);

  }
  EXPORT_SYMBOL(tty_flip_buffer_push);
  
  /**
   *	tty_buffer_init		-	prepare a tty buffer structure

   *	@port: tty port to initialise

   *
   *	Set up the initial state of the buffer management for a tty device.
   *	Must be called before the other tty buffer functions are used.

   */

  void tty_buffer_init(struct tty_port *port)

  {

  	struct tty_bufhead *buf = &port->buf;

  	mutex_init(&buf->lock);

  	tty_buffer_reset(&buf->sentinel, 0);
  	buf->head = &buf->sentinel;
  	buf->tail = &buf->sentinel;

  	init_llist_head(&buf->free);

  	atomic_set(&buf->mem_used, 0);

  	atomic_set(&buf->priority, 0);

  	INIT_WORK(&buf->work, flush_to_ldisc);

  	buf->mem_limit = TTYB_DEFAULT_MEM_LIMIT;

  }

  
  /**
   *	tty_buffer_set_limit	-	change the tty buffer memory limit
   *	@port: tty port to change
   *
   *	Change the tty buffer memory limit.
   *	Must be called before the other tty buffer functions are used.
   */
  
  int tty_buffer_set_limit(struct tty_port *port, int limit)
  {
  	if (limit < MIN_TTYB_SIZE)
  		return -EINVAL;
  	port->buf.mem_limit = limit;
  	return 0;
  }
  EXPORT_SYMBOL_GPL(tty_buffer_set_limit);

  
  /* slave ptys can claim nested buffer lock when handling BRK and INTR */
  void tty_buffer_set_lock_subclass(struct tty_port *port)
  {
  	lockdep_set_subclass(&port->buf.lock, TTY_LOCK_SLAVE);
  }

  
  bool tty_buffer_restart_work(struct tty_port *port)
  {
  	return queue_work(system_unbound_wq, &port->buf.work);
  }
  
  bool tty_buffer_cancel_work(struct tty_port *port)
  {
  	return cancel_work_sync(&port->buf.work);
  }

  
  void tty_buffer_flush_work(struct tty_port *port)
  {
  	flush_work(&port->buf.work);
  }