--- /dev/null
+/*
+ * 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);
+}
Code Review / kvmfornfv.git / blobdiff