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![Peter Hurley](/assets/img/avatar_default.png)
TTY_BUFFER_PAGE is only used within drivers/tty/tty_buffer.c; relocate to that file scope. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
539 lines
14 KiB
C
539 lines
14 KiB
C
/*
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* Tty buffer allocation management
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*/
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#include <linux/types.h>
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#include <linux/errno.h>
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#include <linux/tty.h>
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#include <linux/tty_driver.h>
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#include <linux/tty_flip.h>
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#include <linux/timer.h>
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#include <linux/string.h>
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#include <linux/slab.h>
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#include <linux/sched.h>
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#include <linux/init.h>
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#include <linux/wait.h>
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#include <linux/bitops.h>
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#include <linux/delay.h>
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#include <linux/module.h>
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#include <linux/ratelimit.h>
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#define MIN_TTYB_SIZE 256
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#define TTYB_ALIGN_MASK 255
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/*
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* Byte threshold to limit memory consumption for flip buffers.
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* The actual memory limit is > 2x this amount.
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*/
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#define TTYB_MEM_LIMIT 65536
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/*
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* We default to dicing tty buffer allocations to this many characters
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* in order to avoid multiple page allocations. We know the size of
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* tty_buffer itself but it must also be taken into account that the
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* the buffer is 256 byte aligned. See tty_buffer_find for the allocation
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* logic this must match
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*/
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#define TTY_BUFFER_PAGE (((PAGE_SIZE - sizeof(struct tty_buffer)) / 2) & ~0xFF)
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/**
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* tty_buffer_lock_exclusive - gain exclusive access to buffer
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* tty_buffer_unlock_exclusive - release exclusive access
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*
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* @port - tty_port owning the flip buffer
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*
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* Guarantees safe use of the line discipline's receive_buf() method by
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* excluding the buffer work and any pending flush from using the flip
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* buffer. Data can continue to be added concurrently to the flip buffer
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* from the driver side.
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*
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* On release, the buffer work is restarted if there is data in the
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* flip buffer
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*/
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void tty_buffer_lock_exclusive(struct tty_port *port)
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{
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struct tty_bufhead *buf = &port->buf;
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atomic_inc(&buf->priority);
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mutex_lock(&buf->lock);
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}
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void tty_buffer_unlock_exclusive(struct tty_port *port)
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{
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struct tty_bufhead *buf = &port->buf;
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int restart;
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restart = buf->head->commit != buf->head->read;
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atomic_dec(&buf->priority);
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mutex_unlock(&buf->lock);
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if (restart)
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queue_work(system_unbound_wq, &buf->work);
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}
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/**
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* tty_buffer_space_avail - return unused buffer space
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* @port - tty_port owning the flip buffer
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*
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* Returns the # of bytes which can be written by the driver without
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* reaching the buffer limit.
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*
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* Note: this does not guarantee that memory is available to write
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* the returned # of bytes (use tty_prepare_flip_string_xxx() to
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* pre-allocate if memory guarantee is required).
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*/
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int tty_buffer_space_avail(struct tty_port *port)
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{
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int space = TTYB_MEM_LIMIT - atomic_read(&port->buf.memory_used);
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return max(space, 0);
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}
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static void tty_buffer_reset(struct tty_buffer *p, size_t size)
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{
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p->used = 0;
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p->size = size;
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p->next = NULL;
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p->commit = 0;
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p->read = 0;
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}
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/**
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* tty_buffer_free_all - free buffers used by a tty
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* @tty: tty to free from
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*
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* Remove all the buffers pending on a tty whether queued with data
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* or in the free ring. Must be called when the tty is no longer in use
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*/
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void tty_buffer_free_all(struct tty_port *port)
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{
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struct tty_bufhead *buf = &port->buf;
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struct tty_buffer *p, *next;
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struct llist_node *llist;
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while ((p = buf->head) != NULL) {
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buf->head = p->next;
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if (p->size > 0)
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kfree(p);
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}
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llist = llist_del_all(&buf->free);
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llist_for_each_entry_safe(p, next, llist, free)
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kfree(p);
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tty_buffer_reset(&buf->sentinel, 0);
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buf->head = &buf->sentinel;
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buf->tail = &buf->sentinel;
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atomic_set(&buf->memory_used, 0);
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}
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/**
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* tty_buffer_alloc - allocate a tty buffer
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* @tty: tty device
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* @size: desired size (characters)
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*
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* Allocate a new tty buffer to hold the desired number of characters.
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* We round our buffers off in 256 character chunks to get better
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* allocation behaviour.
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* Return NULL if out of memory or the allocation would exceed the
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* per device queue
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*/
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static struct tty_buffer *tty_buffer_alloc(struct tty_port *port, size_t size)
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{
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struct llist_node *free;
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struct tty_buffer *p;
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/* Round the buffer size out */
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size = __ALIGN_MASK(size, TTYB_ALIGN_MASK);
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if (size <= MIN_TTYB_SIZE) {
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free = llist_del_first(&port->buf.free);
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if (free) {
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p = llist_entry(free, struct tty_buffer, free);
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goto found;
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}
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}
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/* Should possibly check if this fails for the largest buffer we
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have queued and recycle that ? */
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if (atomic_read(&port->buf.memory_used) > TTYB_MEM_LIMIT)
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return NULL;
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p = kmalloc(sizeof(struct tty_buffer) + 2 * size, GFP_ATOMIC);
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if (p == NULL)
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return NULL;
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found:
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tty_buffer_reset(p, size);
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atomic_add(size, &port->buf.memory_used);
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return p;
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}
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/**
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* tty_buffer_free - free a tty buffer
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* @tty: tty owning the buffer
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* @b: the buffer to free
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*
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* Free a tty buffer, or add it to the free list according to our
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* internal strategy
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*/
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static void tty_buffer_free(struct tty_port *port, struct tty_buffer *b)
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{
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struct tty_bufhead *buf = &port->buf;
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/* Dumb strategy for now - should keep some stats */
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WARN_ON(atomic_sub_return(b->size, &buf->memory_used) < 0);
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if (b->size > MIN_TTYB_SIZE)
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kfree(b);
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else if (b->size > 0)
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llist_add(&b->free, &buf->free);
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}
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/**
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* tty_buffer_flush - flush full tty buffers
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* @tty: tty to flush
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*
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* flush all the buffers containing receive data. If the buffer is
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* being processed by flush_to_ldisc then we defer the processing
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* to that function
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*
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* Locking: takes buffer lock to ensure single-threaded flip buffer
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* 'consumer'
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*/
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void tty_buffer_flush(struct tty_struct *tty)
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{
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struct tty_port *port = tty->port;
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struct tty_bufhead *buf = &port->buf;
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struct tty_buffer *next;
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atomic_inc(&buf->priority);
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mutex_lock(&buf->lock);
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while ((next = buf->head->next) != NULL) {
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tty_buffer_free(port, buf->head);
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buf->head = next;
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}
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buf->head->read = buf->head->commit;
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atomic_dec(&buf->priority);
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mutex_unlock(&buf->lock);
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}
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/**
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* tty_buffer_request_room - grow tty buffer if needed
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* @tty: tty structure
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* @size: size desired
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*
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* Make at least size bytes of linear space available for the tty
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* buffer. If we fail return the size we managed to find.
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*/
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int tty_buffer_request_room(struct tty_port *port, size_t size)
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{
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struct tty_bufhead *buf = &port->buf;
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struct tty_buffer *b, *n;
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int left;
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b = buf->tail;
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left = b->size - b->used;
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if (left < size) {
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/* This is the slow path - looking for new buffers to use */
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if ((n = tty_buffer_alloc(port, size)) != NULL) {
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buf->tail = n;
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b->commit = b->used;
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smp_mb();
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b->next = n;
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} else
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size = left;
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}
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return size;
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}
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EXPORT_SYMBOL_GPL(tty_buffer_request_room);
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/**
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* tty_insert_flip_string_fixed_flag - Add characters to the tty buffer
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* @port: tty port
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* @chars: characters
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* @flag: flag value for each character
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* @size: size
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*
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* Queue a series of bytes to the tty buffering. All the characters
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* passed are marked with the supplied flag. Returns the number added.
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*/
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int tty_insert_flip_string_fixed_flag(struct tty_port *port,
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const unsigned char *chars, char flag, size_t size)
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{
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int copied = 0;
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do {
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int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
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int space = tty_buffer_request_room(port, goal);
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struct tty_buffer *tb = port->buf.tail;
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if (unlikely(space == 0))
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break;
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memcpy(char_buf_ptr(tb, tb->used), chars, space);
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memset(flag_buf_ptr(tb, tb->used), flag, space);
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tb->used += space;
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copied += space;
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chars += space;
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/* There is a small chance that we need to split the data over
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several buffers. If this is the case we must loop */
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} while (unlikely(size > copied));
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return copied;
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}
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EXPORT_SYMBOL(tty_insert_flip_string_fixed_flag);
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/**
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* tty_insert_flip_string_flags - Add characters to the tty buffer
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* @port: tty port
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* @chars: characters
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* @flags: flag bytes
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* @size: size
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*
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* Queue a series of bytes to the tty buffering. For each character
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* the flags array indicates the status of the character. Returns the
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* number added.
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*/
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int tty_insert_flip_string_flags(struct tty_port *port,
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const unsigned char *chars, const char *flags, size_t size)
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{
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int copied = 0;
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do {
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int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
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int space = tty_buffer_request_room(port, goal);
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struct tty_buffer *tb = port->buf.tail;
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if (unlikely(space == 0))
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break;
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memcpy(char_buf_ptr(tb, tb->used), chars, space);
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memcpy(flag_buf_ptr(tb, tb->used), flags, space);
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tb->used += space;
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copied += space;
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chars += space;
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flags += space;
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/* There is a small chance that we need to split the data over
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several buffers. If this is the case we must loop */
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} while (unlikely(size > copied));
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return copied;
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}
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EXPORT_SYMBOL(tty_insert_flip_string_flags);
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/**
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* tty_schedule_flip - push characters to ldisc
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* @port: tty port to push from
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*
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* Takes any pending buffers and transfers their ownership to the
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* ldisc side of the queue. It then schedules those characters for
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* processing by the line discipline.
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* Note that this function can only be used when the low_latency flag
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* is unset. Otherwise the workqueue won't be flushed.
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*/
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void tty_schedule_flip(struct tty_port *port)
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{
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struct tty_bufhead *buf = &port->buf;
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WARN_ON(port->low_latency);
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buf->tail->commit = buf->tail->used;
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schedule_work(&buf->work);
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}
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EXPORT_SYMBOL(tty_schedule_flip);
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/**
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* tty_prepare_flip_string - make room for characters
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* @port: tty port
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* @chars: return pointer for character write area
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* @size: desired size
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*
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* Prepare a block of space in the buffer for data. Returns the length
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* available and buffer pointer to the space which is now allocated and
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* accounted for as ready for normal characters. This is used for drivers
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* that need their own block copy routines into the buffer. There is no
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* guarantee the buffer is a DMA target!
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*/
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int tty_prepare_flip_string(struct tty_port *port, unsigned char **chars,
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size_t size)
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{
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int space = tty_buffer_request_room(port, size);
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if (likely(space)) {
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struct tty_buffer *tb = port->buf.tail;
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*chars = char_buf_ptr(tb, tb->used);
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memset(flag_buf_ptr(tb, tb->used), TTY_NORMAL, space);
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tb->used += space;
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}
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return space;
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}
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EXPORT_SYMBOL_GPL(tty_prepare_flip_string);
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/**
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* tty_prepare_flip_string_flags - make room for characters
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* @port: tty port
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* @chars: return pointer for character write area
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* @flags: return pointer for status flag write area
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* @size: desired size
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*
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* Prepare a block of space in the buffer for data. Returns the length
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* available and buffer pointer to the space which is now allocated and
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* accounted for as ready for characters. This is used for drivers
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* that need their own block copy routines into the buffer. There is no
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* guarantee the buffer is a DMA target!
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*/
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int tty_prepare_flip_string_flags(struct tty_port *port,
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unsigned char **chars, char **flags, size_t size)
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{
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int space = tty_buffer_request_room(port, size);
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if (likely(space)) {
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struct tty_buffer *tb = port->buf.tail;
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*chars = char_buf_ptr(tb, tb->used);
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*flags = flag_buf_ptr(tb, tb->used);
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tb->used += space;
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}
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return space;
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}
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EXPORT_SYMBOL_GPL(tty_prepare_flip_string_flags);
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static int
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receive_buf(struct tty_struct *tty, struct tty_buffer *head, int count)
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{
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struct tty_ldisc *disc = tty->ldisc;
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unsigned char *p = char_buf_ptr(head, head->read);
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char *f = flag_buf_ptr(head, head->read);
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if (disc->ops->receive_buf2)
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count = disc->ops->receive_buf2(tty, p, f, count);
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else {
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count = min_t(int, count, tty->receive_room);
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if (count)
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disc->ops->receive_buf(tty, p, f, count);
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}
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head->read += count;
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return count;
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}
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/**
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* flush_to_ldisc
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* @work: tty structure passed from work queue.
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*
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* This routine is called out of the software interrupt to flush data
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* from the buffer chain to the line discipline.
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*
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* The receive_buf method is single threaded for each tty instance.
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*
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* Locking: takes buffer lock to ensure single-threaded flip buffer
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* 'consumer'
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*/
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static void flush_to_ldisc(struct work_struct *work)
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{
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struct tty_port *port = container_of(work, struct tty_port, buf.work);
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struct tty_bufhead *buf = &port->buf;
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struct tty_struct *tty;
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struct tty_ldisc *disc;
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tty = port->itty;
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if (tty == NULL)
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return;
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disc = tty_ldisc_ref(tty);
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if (disc == NULL)
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return;
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mutex_lock(&buf->lock);
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while (1) {
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struct tty_buffer *head = buf->head;
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int count;
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/* Ldisc or user is trying to gain exclusive access */
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if (atomic_read(&buf->priority))
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break;
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count = head->commit - head->read;
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if (!count) {
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if (head->next == NULL)
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break;
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buf->head = head->next;
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tty_buffer_free(port, head);
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continue;
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}
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count = receive_buf(tty, head, count);
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if (!count)
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break;
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}
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mutex_unlock(&buf->lock);
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tty_ldisc_deref(disc);
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}
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/**
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* tty_flush_to_ldisc
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* @tty: tty to push
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*
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* Push the terminal flip buffers to the line discipline.
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*
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* Must not be called from IRQ context.
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*/
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void tty_flush_to_ldisc(struct tty_struct *tty)
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{
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if (!tty->port->low_latency)
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flush_work(&tty->port->buf.work);
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}
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/**
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* tty_flip_buffer_push - terminal
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* @port: tty port to push
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*
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* Queue a push of the terminal flip buffers to the line discipline. This
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* function must not be called from IRQ context if port->low_latency is
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* set.
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*
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* In the event of the queue being busy for flipping the work will be
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* held off and retried later.
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*/
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void tty_flip_buffer_push(struct tty_port *port)
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{
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struct tty_bufhead *buf = &port->buf;
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buf->tail->commit = buf->tail->used;
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if (port->low_latency)
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flush_to_ldisc(&buf->work);
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else
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schedule_work(&buf->work);
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}
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EXPORT_SYMBOL(tty_flip_buffer_push);
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/**
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* tty_buffer_init - prepare a tty buffer structure
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* @tty: tty to initialise
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*
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* Set up the initial state of the buffer management for a tty device.
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* Must be called before the other tty buffer functions are used.
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*/
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void tty_buffer_init(struct tty_port *port)
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{
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struct tty_bufhead *buf = &port->buf;
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|
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mutex_init(&buf->lock);
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tty_buffer_reset(&buf->sentinel, 0);
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buf->head = &buf->sentinel;
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buf->tail = &buf->sentinel;
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init_llist_head(&buf->free);
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atomic_set(&buf->memory_used, 0);
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atomic_set(&buf->priority, 0);
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INIT_WORK(&buf->work, flush_to_ldisc);
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}
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