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    Subject[PATCH 23/76] tty: split the buffering from tty_io
    Date
    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>
    ---

    drivers/char/Makefile | 2
    drivers/char/tty_buffer.c | 511 +++++++++++++++++++++++++++++++++++++++++++++
    drivers/char/tty_io.c | 502 --------------------------------------------
    include/linux/tty.h | 3
    4 files changed, 515 insertions(+), 503 deletions(-)
    create mode 100644 drivers/char/tty_buffer.c

    diff --git a/drivers/char/Makefile b/drivers/char/Makefile
    index 6850f6d..77ea41b 100644
    --- a/drivers/char/Makefile
    +++ b/drivers/char/Makefile
    @@ -7,7 +7,7 @@
    #
    FONTMAPFILE = cp437.uni

    -obj-y += mem.o random.o tty_io.o n_tty.o tty_ioctl.o tty_ldisc.o
    +obj-y += mem.o random.o tty_io.o n_tty.o tty_ioctl.o tty_ldisc.o tty_buffer.o

    obj-$(CONFIG_LEGACY_PTYS) += pty.o
    obj-$(CONFIG_UNIX98_PTYS) += pty.o
    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);
    +}
    +
    diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
    index 2f05728..3a72693 100644
    --- a/drivers/char/tty_io.c
    +++ b/drivers/char/tty_io.c
    @@ -176,8 +176,6 @@ static struct tty_struct *alloc_tty_struct(void)
    return kzalloc(sizeof(struct tty_struct), GFP_KERNEL);
    }

    -static void tty_buffer_free_all(struct tty_struct *);
    -
    /**
    * free_tty_struct - free a disused tty
    * @tty: tty struct to free
    @@ -263,398 +261,6 @@ static int check_tty_count(struct tty_struct *tty, const char *routine)
    return 0;
    }

    -/*
    - * Tty buffer allocation management
    - */
    -
    -/**
    - * 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
    - */
    -
    -static 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_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
    - */
    -
    -static 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;
    -}
    -
    -/**
    - * 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
    - */
    -
    -static 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);
    -
    -
    -
    /**
    * get_tty_driver - find device of a tty
    * @dev_t: device identifier
    @@ -3216,113 +2822,6 @@ void do_SAK(struct tty_struct *tty)
    EXPORT_SYMBOL(do_SAK);

    /**
    - * 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);
    -
    -
    -/**
    * initialize_tty_struct
    * @tty: tty to initialize
    *
    @@ -3342,7 +2841,6 @@ static void initialize_tty_struct(struct tty_struct *tty)
    tty->overrun_time = jiffies;
    tty->buf.head = tty->buf.tail = NULL;
    tty_buffer_init(tty);
    - INIT_DELAYED_WORK(&tty->buf.work, flush_to_ldisc);
    mutex_init(&tty->termios_mutex);
    init_waitqueue_head(&tty->write_wait);
    init_waitqueue_head(&tty->read_wait);
    diff --git a/include/linux/tty.h b/include/linux/tty.h
    index 0cbec74..7271c62 100644
    --- a/include/linux/tty.h
    +++ b/include/linux/tty.h
    @@ -347,6 +347,9 @@ extern void __do_SAK(struct tty_struct *tty);
    extern void disassociate_ctty(int priv);
    extern void no_tty(void);
    extern void tty_flip_buffer_push(struct tty_struct *tty);
    +extern void tty_buffer_free_all(struct tty_struct *tty);
    +extern void tty_buffer_flush(struct tty_struct *tty);
    +extern void tty_buffer_init(struct tty_struct *tty);
    extern speed_t tty_get_baud_rate(struct tty_struct *tty);
    extern speed_t tty_termios_baud_rate(struct ktermios *termios);
    extern speed_t tty_termios_input_baud_rate(struct ktermios *termios);


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