1 files changed, 578 insertions, 0 deletions
diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
new file mode 100644
index 000000000..2f78b77f0
--- /dev/null
+++ b/drivers/tty/tty_buffer.c
@@ -0,0 +1,578 @@
+/*
+ * 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	65536
+
+/*
+ * 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)
+
+/*
+ * If all tty flip buffers have been processed by flush_to_ldisc() or
+ * dropped by tty_buffer_flush(), check if the linked pty has been closed.
+ * If so, wake the reader/poll to process
+ */
+static inline void check_other_closed(struct tty_struct *tty)
+{
+	unsigned long flags, old;
+
+	/* transition from TTY_OTHER_CLOSED => TTY_OTHER_DONE must be atomic */
+	for (flags = ACCESS_ONCE(tty->flags);
+	     test_bit(TTY_OTHER_CLOSED, &flags);
+	     ) {
+		old = flags;
+		__set_bit(TTY_OTHER_DONE, &flags);
+		flags = cmpxchg(&tty->flags, old, flags);
+		if (old == flags) {
+			wake_up_interruptible(&tty->read_wait);
+			break;
+		}
+	}
+}
+
+/**
+ *	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
+ *	@tty: tty 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;
+
+	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);
+
+	tty_buffer_reset(&buf->sentinel, 0);
+	buf->head = &buf->sentinel;
+	buf->tail = &buf->sentinel;
+
+	atomic_set(&buf->mem_used, 0);
+}
+
+/**
+ *	tty_buffer_alloc	-	allocate a tty buffer
+ *	@tty: tty device
+ *	@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
+ *	@tty: tty 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);
+	while ((next = 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);
+
+	check_other_closed(tty);
+
+	atomic_dec(&buf->priority);
+	mutex_unlock(&buf->lock);
+}
+
+/**
+ *	tty_buffer_request_room		-	grow tty buffer if needed
+ *	@tty: tty structure
+ *	@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 */
+		if ((n = tty_buffer_alloc(port, size)) != NULL) {
+			n->flags = flags;
+			buf->tail = n;
+			b->commit = b->used;
+			/* paired w/ barrier in flush_to_ldisc(); ensures the
+			 * latest commit value can be read before the head is
+			 * advanced to the next buffer
+			 */
+			smp_wmb();
+			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_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;
+
+	buf->tail->commit = buf->tail->used;
+	schedule_work(&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);
+
+
+static int
+receive_buf(struct tty_struct *tty, struct tty_buffer *head, int count)
+{
+	struct tty_ldisc *disc = tty->ldisc;
+	unsigned char *p = char_buf_ptr(head, head->read);
+	char	      *f = NULL;
+
+	if (~head->flags & TTYB_NORMAL)
+		f = flag_buf_ptr(head, head->read);
+
+	if (disc->ops->receive_buf2)
+		count = disc->ops->receive_buf2(tty, p, f, count);
+	else {
+		count = min_t(int, count, tty->receive_room);
+		if (count)
+			disc->ops->receive_buf(tty, p, f, count);
+	}
+	head->read += count;
+	return count;
+}
+
+/**
+ *	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;
+	struct tty_struct *tty;
+	struct tty_ldisc *disc;
+
+	tty = port->itty;
+	if (tty == NULL)
+		return;
+
+	disc = tty_ldisc_ref(tty);
+	if (disc == NULL)
+		return;
+
+	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;
+
+		next = head->next;
+		/* paired w/ barrier in __tty_buffer_request_room();
+		 * ensures commit value read is not stale if the head
+		 * is advancing to the next buffer
+		 */
+		smp_rmb();
+		count = head->commit - head->read;
+		if (!count) {
+			if (next == NULL) {
+				check_other_closed(tty);
+				break;
+			}
+			buf->head = next;
+			tty_buffer_free(port, head);
+			continue;
+		}
+
+		count = receive_buf(tty, head, count);
+		if (!count)
+			break;
+	}
+
+	mutex_unlock(&buf->lock);
+
+	tty_ldisc_deref(disc);
+}
+
+/**
+ *	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
+ *	@tty: tty 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);
+}