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>

1 files changed, 511 insertions, 0 deletions

diff --git a/drivers/char/tty_buffer.c b/drivers/char/tty_buffer.c
new file mode 100644
index 000000000000..810ee25d66a4
--- /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);
+}
+