tty: split the buffering from tty_io
The two are basically independent chunks of code so lets split them up for
readability and sanity. It also makes the API boundaries much clearer.
Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/drivers/char/tty_buffer.c b/drivers/char/tty_buffer.c
new file mode 100644
index 0000000..810ee25
--- /dev/null
+++ b/drivers/char/tty_buffer.c
@@ -0,0 +1,511 @@
+/*
+ * 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/init.h>
+#include <linux/wait.h>
+#include <linux/bitops.h>
+#include <linux/delay.h>
+#include <linux/module.h>
+
+/**
+ * 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
+ *
+ * Locking: none
+ */
+
+void tty_buffer_free_all(struct tty_struct *tty)
+{
+ struct tty_buffer *thead;
+ while ((thead = tty->buf.head) != NULL) {
+ tty->buf.head = thead->next;
+ kfree(thead);
+ }
+ while ((thead = tty->buf.free) != NULL) {
+ tty->buf.free = thead->next;
+ kfree(thead);
+ }
+ tty->buf.tail = NULL;
+ tty->buf.memory_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.
+ * Return NULL if out of memory or the allocation would exceed the
+ * per device queue
+ *
+ * Locking: Caller must hold tty->buf.lock
+ */
+
+static struct tty_buffer *tty_buffer_alloc(struct tty_struct *tty, size_t size)
+{
+ struct tty_buffer *p;
+
+ if (tty->buf.memory_used + size > 65536)
+ return NULL;
+ p = kmalloc(sizeof(struct tty_buffer) + 2 * size, GFP_ATOMIC);
+ if (p == NULL)
+ return NULL;
+ p->used = 0;
+ p->size = size;
+ p->next = NULL;
+ p->commit = 0;
+ p->read = 0;
+ p->char_buf_ptr = (char *)(p->data);
+ p->flag_buf_ptr = (unsigned char *)p->char_buf_ptr + size;
+ tty->buf.memory_used += size;
+ 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
+ *
+ * Locking: Caller must hold tty->buf.lock
+ */
+
+static void tty_buffer_free(struct tty_struct *tty, struct tty_buffer *b)
+{
+ /* Dumb strategy for now - should keep some stats */
+ tty->buf.memory_used -= b->size;
+ WARN_ON(tty->buf.memory_used < 0);
+
+ if (b->size >= 512)
+ kfree(b);
+ else {
+ b->next = tty->buf.free;
+ tty->buf.free = b;
+ }
+}
+
+/**
+ * __tty_buffer_flush - flush full tty buffers
+ * @tty: tty to flush
+ *
+ * flush all the buffers containing receive data. Caller must
+ * hold the buffer lock and must have ensured no parallel flush to
+ * ldisc is running.
+ *
+ * Locking: Caller must hold tty->buf.lock
+ */
+
+static void __tty_buffer_flush(struct tty_struct *tty)
+{
+ struct tty_buffer *thead;
+
+ while ((thead = tty->buf.head) != NULL) {
+ tty->buf.head = thead->next;
+ tty_buffer_free(tty, thead);
+ }
+ tty->buf.tail = NULL;
+}
+
+/**
+ * tty_buffer_flush - flush full tty buffers
+ * @tty: tty to flush
+ *
+ * flush all the buffers containing receive data. If the buffer is
+ * being processed by flush_to_ldisc then we defer the processing
+ * to that function
+ *
+ * Locking: none
+ */
+
+void tty_buffer_flush(struct tty_struct *tty)
+{
+ unsigned long flags;
+ spin_lock_irqsave(&tty->buf.lock, flags);
+
+ /* If the data is being pushed to the tty layer then we can't
+ process it here. Instead set a flag and the flush_to_ldisc
+ path will process the flush request before it exits */
+ if (test_bit(TTY_FLUSHING, &tty->flags)) {
+ set_bit(TTY_FLUSHPENDING, &tty->flags);
+ spin_unlock_irqrestore(&tty->buf.lock, flags);
+ wait_event(tty->read_wait,
+ test_bit(TTY_FLUSHPENDING, &tty->flags) == 0);
+ return;
+ } else
+ __tty_buffer_flush(tty);
+ spin_unlock_irqrestore(&tty->buf.lock, flags);
+}
+
+/**
+ * tty_buffer_find - find a free tty buffer
+ * @tty: tty owning the buffer
+ * @size: characters wanted
+ *
+ * Locate an existing suitable tty buffer or if we are lacking one then
+ * allocate a new one. We round our buffers off in 256 character chunks
+ * to get better allocation behaviour.
+ *
+ * Locking: Caller must hold tty->buf.lock
+ */
+
+static struct tty_buffer *tty_buffer_find(struct tty_struct *tty, size_t size)
+{
+ struct tty_buffer **tbh = &tty->buf.free;
+ while ((*tbh) != NULL) {
+ struct tty_buffer *t = *tbh;
+ if (t->size >= size) {
+ *tbh = t->next;
+ t->next = NULL;
+ t->used = 0;
+ t->commit = 0;
+ t->read = 0;
+ tty->buf.memory_used += t->size;
+ return t;
+ }
+ tbh = &((*tbh)->next);
+ }
+ /* Round the buffer size out */
+ size = (size + 0xFF) & ~0xFF;
+ return tty_buffer_alloc(tty, size);
+ /* Should possibly check if this fails for the largest buffer we
+ have queued and recycle that ? */
+}
+
+/**
+ * tty_buffer_request_room - grow tty buffer if needed
+ * @tty: tty structure
+ * @size: size desired
+ *
+ * Make at least size bytes of linear space available for the tty
+ * buffer. If we fail return the size we managed to find.
+ *
+ * Locking: Takes tty->buf.lock
+ */
+int tty_buffer_request_room(struct tty_struct *tty, size_t size)
+{
+ struct tty_buffer *b, *n;
+ int left;
+ unsigned long flags;
+
+ spin_lock_irqsave(&tty->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 */
+ if ((b = tty->buf.tail) != 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_find(tty, size)) != NULL) {
+ if (b != NULL) {
+ b->next = n;
+ b->commit = b->used;
+ } else
+ tty->buf.head = n;
+ tty->buf.tail = n;
+ } else
+ size = left;
+ }
+
+ spin_unlock_irqrestore(&tty->buf.lock, flags);
+ return size;
+}
+EXPORT_SYMBOL_GPL(tty_buffer_request_room);
+
+/**
+ * tty_insert_flip_string - Add characters to the tty buffer
+ * @tty: tty structure
+ * @chars: characters
+ * @size: size
+ *
+ * Queue a series of bytes to the tty buffering. All the characters
+ * passed are marked as without error. Returns the number added.
+ *
+ * Locking: Called functions may take tty->buf.lock
+ */
+
+int tty_insert_flip_string(struct tty_struct *tty, const unsigned char *chars,
+ size_t size)
+{
+ int copied = 0;
+ do {
+ int space = tty_buffer_request_room(tty, size - copied);
+ struct tty_buffer *tb = tty->buf.tail;
+ /* If there is no space then tb may be NULL */
+ if (unlikely(space == 0))
+ break;
+ memcpy(tb->char_buf_ptr + tb->used, chars, space);
+ memset(tb->flag_buf_ptr + tb->used, TTY_NORMAL, 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);
+
+/**
+ * tty_insert_flip_string_flags - Add characters to the tty buffer
+ * @tty: tty structure
+ * @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.
+ *
+ * Locking: Called functions may take tty->buf.lock
+ */
+
+int tty_insert_flip_string_flags(struct tty_struct *tty,
+ const unsigned char *chars, const char *flags, size_t size)
+{
+ int copied = 0;
+ do {
+ int space = tty_buffer_request_room(tty, size - copied);
+ struct tty_buffer *tb = tty->buf.tail;
+ /* If there is no space then tb may be NULL */
+ if (unlikely(space == 0))
+ break;
+ memcpy(tb->char_buf_ptr + tb->used, chars, space);
+ memcpy(tb->flag_buf_ptr + 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
+ * @tty: tty 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.
+ *
+ * Locking: Takes tty->buf.lock
+ */
+
+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->commit = tty->buf.tail->used;
+ spin_unlock_irqrestore(&tty->buf.lock, flags);
+ schedule_delayed_work(&tty->buf.work, 1);
+}
+EXPORT_SYMBOL(tty_schedule_flip);
+
+/**
+ * tty_prepare_flip_string - make room for characters
+ * @tty: tty
+ * @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!
+ *
+ * Locking: May call functions taking tty->buf.lock
+ */
+
+int tty_prepare_flip_string(struct tty_struct *tty, unsigned char **chars,
+ size_t size)
+{
+ int space = tty_buffer_request_room(tty, size);
+ if (likely(space)) {
+ struct tty_buffer *tb = tty->buf.tail;
+ *chars = tb->char_buf_ptr + tb->used;
+ memset(tb->flag_buf_ptr + tb->used, TTY_NORMAL, space);
+ tb->used += space;
+ }
+ return space;
+}
+EXPORT_SYMBOL_GPL(tty_prepare_flip_string);
+
+/**
+ * tty_prepare_flip_string_flags - make room for characters
+ * @tty: tty
+ * @chars: return pointer for character write area
+ * @flags: return pointer for status flag 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 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!
+ *
+ * Locking: May call functions taking tty->buf.lock
+ */
+
+int tty_prepare_flip_string_flags(struct tty_struct *tty,
+ unsigned char **chars, char **flags, size_t size)
+{
+ int space = tty_buffer_request_room(tty, size);
+ if (likely(space)) {
+ struct tty_buffer *tb = tty->buf.tail;
+ *chars = tb->char_buf_ptr + tb->used;
+ *flags = tb->flag_buf_ptr + tb->used;
+ tb->used += space;
+ }
+ return space;
+}
+EXPORT_SYMBOL_GPL(tty_prepare_flip_string_flags);
+
+
+
+/**
+ * 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.
+ *
+ * Locking: holds tty->buf.lock to guard buffer list. Drops the lock
+ * while invoking the line discipline receive_buf method. The
+ * receive_buf method is single threaded for each tty instance.
+ */
+
+static void flush_to_ldisc(struct work_struct *work)
+{
+ struct tty_struct *tty =
+ container_of(work, struct tty_struct, buf.work.work);
+ unsigned long flags;
+ struct tty_ldisc *disc;
+ struct tty_buffer *tbuf, *head;
+ char *char_buf;
+ unsigned char *flag_buf;
+
+ disc = tty_ldisc_ref(tty);
+ if (disc == NULL) /* !TTY_LDISC */
+ return;
+
+ spin_lock_irqsave(&tty->buf.lock, flags);
+ /* So we know a flush is running */
+ set_bit(TTY_FLUSHING, &tty->flags);
+ head = tty->buf.head;
+ if (head != NULL) {
+ tty->buf.head = NULL;
+ for (;;) {
+ int count = head->commit - head->read;
+ if (!count) {
+ if (head->next == NULL)
+ break;
+ tbuf = head;
+ head = head->next;
+ tty_buffer_free(tty, tbuf);
+ continue;
+ }
+ /* Ldisc or user is trying to flush the buffers
+ we are feeding to the ldisc, stop feeding the
+ line discipline as we want to empty the queue */
+ if (test_bit(TTY_FLUSHPENDING, &tty->flags))
+ break;
+ if (!tty->receive_room) {
+ schedule_delayed_work(&tty->buf.work, 1);
+ break;
+ }
+ if (count > tty->receive_room)
+ count = tty->receive_room;
+ char_buf = head->char_buf_ptr + head->read;
+ flag_buf = head->flag_buf_ptr + head->read;
+ head->read += count;
+ spin_unlock_irqrestore(&tty->buf.lock, flags);
+ disc->ops->receive_buf(tty, char_buf,
+ flag_buf, count);
+ spin_lock_irqsave(&tty->buf.lock, flags);
+ }
+ /* Restore the queue head */
+ tty->buf.head = head;
+ }
+ /* We may have a deferred request to flush the input buffer,
+ if so pull the chain under the lock and empty the queue */
+ if (test_bit(TTY_FLUSHPENDING, &tty->flags)) {
+ __tty_buffer_flush(tty);
+ clear_bit(TTY_FLUSHPENDING, &tty->flags);
+ wake_up(&tty->read_wait);
+ }
+ clear_bit(TTY_FLUSHING, &tty->flags);
+ spin_unlock_irqrestore(&tty->buf.lock, flags);
+
+ tty_ldisc_deref(disc);
+}
+
+/**
+ * tty_flip_buffer_push - terminal
+ * @tty: tty to push
+ *
+ * Queue a push of the terminal flip buffers to the line discipline. This
+ * function must not be called from IRQ context if tty->low_latency is set.
+ *
+ * In the event of the queue being busy for flipping the work will be
+ * held off and retried later.
+ *
+ * Locking: tty buffer lock. Driver locks in low latency mode.
+ */
+
+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->commit = tty->buf.tail->used;
+ spin_unlock_irqrestore(&tty->buf.lock, flags);
+
+ if (tty->low_latency)
+ flush_to_ldisc(&tty->buf.work.work);
+ else
+ schedule_delayed_work(&tty->buf.work, 1);
+}
+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.
+ *
+ * Locking: none
+ */
+
+void tty_buffer_init(struct tty_struct *tty)
+{
+ spin_lock_init(&tty->buf.lock);
+ tty->buf.head = NULL;
+ tty->buf.tail = NULL;
+ tty->buf.free = NULL;
+ tty->buf.memory_used = 0;
+ INIT_DELAYED_WORK(&tty->buf.work, flush_to_ldisc);
+}
+