diff options
Diffstat (limited to 'drivers/tty/tty_buffer.c')
| -rw-r--r-- | drivers/tty/tty_buffer.c | 534 |
1 files changed, 534 insertions, 0 deletions
diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c new file mode 100644 index 000000000000..d8210ca00720 --- /dev/null +++ b/drivers/tty/tty_buffer.c @@ -0,0 +1,534 @@ +/* + * 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); +} + |