/*
 * 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_fixed_flag - Add characters to the tty buffer
 *      @tty: tty structure
 *      @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.
 *
 *      Locking: Called functions may take tty->buf.lock
 */

int tty_insert_flip_string_fixed_flag(struct tty_struct *tty,
                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 space = tty_buffer_request_room(tty, goal);
                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, 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
 *      @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 goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
                int space = tty_buffer_request_room(tty, goal);
                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;

        disc = tty_ldisc_ref(tty);
        if (disc == NULL)       /*  !TTY_LDISC */
                return;

        spin_lock_irqsave(&tty->buf.lock, flags);

        if (!test_and_set_bit(TTY_FLUSHING, &tty->flags)) {
                struct tty_buffer *head, *tail = tty->buf.tail;
                int seen_tail = 0;
                while ((head = tty->buf.head) != NULL) {
                        int count;
                        char *char_buf;
                        unsigned char *flag_buf;

                        count = head->commit - head->read;
                        if (!count) {
                                if (head->next == NULL)
                                        break;
                                /*
                                  There's a possibility tty might get new buffer
                                  added during the unlock window below. We could
                                  end up spinning in here forever hogging the CPU
                                  completely. To avoid this let's have a rest each
                                  time we processed the tail buffer.
                                */
                                if (tail == head)
                                        seen_tail = 1;
                                tty->buf.head = head->next;
                                tty_buffer_free(tty, head);
                                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 || seen_tail) {
                                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);
                }
                clear_bit(TTY_FLUSHING, &tty->flags);
        }

        /* 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);
        }
        spin_unlock_irqrestore(&tty->buf.lock, flags);

        tty_ldisc_deref(disc);
}

/**
 *      tty_flush_to_ldisc
 *      @tty: tty to push
 *
 *      Push the terminal flip buffers to the line discipline.
 *
 *      Must not be called from IRQ context.
 */
void tty_flush_to_ldisc(struct tty_struct *tty)
{
        flush_delayed_work(&tty->buf.work);
}

/**
 *      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);
}