/*
* 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/wait.h>
#include <linux/bitops.h>
#include <linux/delay.h>
#include <linux/module.h>
#include <linux/ratelimit.h>
#define MIN_TTYB_SIZE 256
#define TTYB_ALIGN_MASK 255
/*
* Byte threshold to limit memory consumption for flip buffers.
* The actual memory limit is > 2x this amount.
*/
#define TTYB_DEFAULT_MEM_LIMIT 65536
/*
* We default to dicing tty buffer allocations to this many characters
* in order to avoid multiple page allocations. We know the size of
* tty_buffer itself but it must also be taken into account that the
* the buffer is 256 byte aligned. See tty_buffer_find for the allocation
* logic this must match
*/
#define TTY_BUFFER_PAGE (((PAGE_SIZE - sizeof(struct tty_buffer)) / 2) & ~0xFF)
/*
* If all tty flip buffers have been processed by flush_to_ldisc() or
* dropped by tty_buffer_flush(), check if the linked pty has been closed.
* If so, wake the reader/poll to process
*/
static inline void check_other_closed(struct tty_struct *tty)
{
unsigned long flags, old;
/* transition from TTY_OTHER_CLOSED => TTY_OTHER_DONE must be atomic */
for (flags = ACCESS_ONCE(tty->flags);
test_bit(TTY_OTHER_CLOSED, &flags);
) {
old = flags;
__set_bit(TTY_OTHER_DONE, &flags);
flags = cmpxchg(&tty->flags, old, flags);
if (old == flags) {
wake_up_interruptible(&tty->read_wait);
break;
}
}
}
/**
* tty_buffer_lock_exclusive - gain exclusive access to buffer
* tty_buffer_unlock_exclusive - release exclusive access
*
* @port - tty_port owning the flip buffer
*
* Guarantees safe use of the line discipline's receive_buf() method by
* excluding the buffer work and any pending flush from using the flip
* buffer. Data can continue to be added concurrently to the flip buffer
* from the driver side.
*
* On release, the buffer work is restarted if there is data in the
* flip buffer
*/
void tty_buffer_lock_exclusive(struct tty_port *port)
{
struct tty_bufhead *buf = &port->buf;
atomic_inc(&buf->priority);
mutex_lock(&buf->lock);
}
EXPORT_SYMBOL_GPL(tty_buffer_lock_exclusive);
void tty_buffer_unlock_exclusive(struct tty_port *port)
{
struct tty_bufhead *buf = &port->buf;
int restart;
restart = buf->head->commit != buf->head->read;
atomic_dec(&buf->priority);
mutex_unlock(&buf->lock);
if (restart)
queue_work(system_unbound_wq, &buf->work);
}
EXPORT_SYMBOL_GPL(tty_buffer_unlock_exclusive);
/**
* tty_buffer_space_avail - return unused buffer space
* @port - tty_port owning the flip buffer
*
* Returns the # of bytes which can be written by the driver without
* reaching the buffer limit.
*
* Note: this does not guarantee that memory is available to write
* the returned # of bytes (use tty_prepare_flip_string_xxx() to
* pre-allocate if memory guarantee is required).
*/
int tty_buffer_space_avail(struct tty_port *port)
{
int space = port->buf.mem_limit - atomic_read(&port->buf.mem_used);
return max(space, 0);
}
EXPORT_SYMBOL_GPL(tty_buffer_space_avail);
static void tty_buffer_reset(struct tty_buffer *p, size_t size)
{
p->used = 0;
p->size = size;
p->next = NULL;
p->commit = 0;
p->read = 0;
p->flags = 0;
}
/**
* 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
*/
void tty_buffer_free_all(struct tty_port *port)
{
struct tty_bufhead *buf = &port->buf;
struct tty_buffer *p, *next;
struct llist_node *llist;
while ((p = buf->head) != NULL) {
buf->head = p->next;
if (p->size > 0)
kfree(p);
}
llist = llist_del_all(&buf->free);
llist_for_each_entry_safe(p, next, llist, free)
kfree(p);
tty_buffer_reset(&buf->sentinel, 0);
buf->head = &buf->sentinel;
buf->tail = &buf->sentinel;
atomic_set(&buf->mem_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.
* We round our buffers off in 256 character chunks to get better
* allocation behaviour.
* Return NULL if out of memory or the allocation would exceed the
* per device queue
*/
static struct tty_buffer *tty_buffer_alloc(struct tty_port *port, size_t size)
{
struct llist_node *free;
struct tty_buffer *p;
/* Round the buffer size out */
size = __ALIGN_MASK(size, TTYB_ALIGN_MASK);
if (size <= MIN_TTYB_SIZE) {
free = llist_del_first(&port->buf.free);
if (free) {
p = llist_entry(free, struct tty_buffer, free);
goto found;
}
}
/* Should possibly check if this fails for the largest buffer we
have queued and recycle that ? */
if (atomic_read(&port->buf.mem_used) > port->buf.mem_limit)
return NULL;
p = kmalloc(sizeof(struct tty_buffer) + 2 * size, GFP_ATOMIC);
if (p == NULL)
return NULL;
found:
tty_buffer_reset(p, size);
atomic_add(size, &port->buf.mem_used);
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
*/
static void tty_buffer_free(struct tty_port *port, struct tty_buffer *b)
{
struct tty_bufhead *buf = &port->buf;
/* Dumb strategy for now - should keep some stats */
WARN_ON(atomic_sub_return(b->size, &buf->mem_used) < 0);
if (b->size > MIN_TTYB_SIZE)
kfree(b);
else if (b->size > 0)
llist_add(&b->free, &buf->free);
}
/**
* tty_buffer_flush - flush full tty buffers
* @tty: tty to flush
* @ld: optional ldisc ptr (must be referenced)
*
* flush all the buffers containing receive data. If ld != NULL,
* flush the ldisc input buffer.
*
* Locking: takes buffer lock to ensure single-threaded flip buffer
* 'consumer'
*/
void tty_buffer_flush(struct tty_struct *tty, struct tty_ldisc *ld)
{
struct tty_port *port = tty->port;
struct tty_bufhead *buf = &port->buf;
struct tty_buffer *next;
atomic_inc(&buf->priority);
mutex_lock(&buf->lock);
/* paired w/ release in __tty_buffer_request_room; ensures there are
* no pending memory accesses to the freed buffer
*/
while ((next = smp_load_acquire(&buf->head->next)) != NULL) {
tty_buffer_free(port, buf->head);
buf->head = next;
}
buf->head->read = buf->head->commit;
if (ld && ld->ops->flush_buffer)
ld->ops->flush_buffer(tty);
check_other_closed(tty);
atomic_dec(&buf->priority);
mutex_unlock(&buf->lock);
}
/**
* tty_buffer_request_room - grow tty buffer if needed
* @tty: tty structure
* @size: size desired
* @flags: buffer flags if new buffer allocated (default = 0)
*
* Make at least size bytes of linear space available for the tty
* buffer. If we fail return the size we managed to find.
*
* Will change over to a new buffer if the current buffer is encoded as
* TTY_NORMAL (so has no flags buffer) and the new buffer requires
* a flags buffer.
*/
static int __tty_buffer_request_room(struct tty_port *port, size_t size,
int flags)
{
struct tty_bufhead *buf = &port->buf;
struct tty_buffer *b, *n;
int left, change;
b = buf->tail;
if (b->flags & TTYB_NORMAL)
left = 2 * b->size - b->used;
else
left = b->size - b->used;
change = (b->flags & TTYB_NORMAL) && (~flags & TTYB_NORMAL);
if (change || left < size) {
/* This is the slow path - looking for new buffers to use */
n = tty_buffer_alloc(port, size);
if (n != NULL) {
n->flags = flags;
buf->tail = n;
/* paired w/ acquire in flush_to_ldisc(); ensures
* flush_to_ldisc() sees buffer data.
*/
smp_store_release(&b->commit, b->used);
/* paired w/ acquire in flush_to_ldisc(); ensures the
* latest commit value can be read before the head is
* advanced to the next buffer
*/
smp_store_release(&b->next, n);
} else if (change)
size = 0;
else
size = left;
}
return size;
}
int tty_buffer_request_room(struct tty_port *port, size_t size)
{
return __tty_buffer_request_room(port, size, 0);
}
EXPORT_SYMBOL_GPL(tty_buffer_request_room);
/**
* tty_insert_flip_string_fixed_flag - Add characters to the tty buffer
* @port: tty port
* @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.
*/
int tty_insert_flip_string_fixed_flag(struct tty_port *port,
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 flags = (flag == TTY_NORMAL) ? TTYB_NORMAL : 0;
int space = __tty_buffer_request_room(port, goal, flags);
struct tty_buffer *tb = port->buf.tail;
if (unlikely(space == 0))
break;
memcpy(char_buf_ptr(tb, tb->used), chars, space);
if (~tb->flags & TTYB_NORMAL)
memset(flag_buf_ptr(tb, 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
* @port: tty port
* @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.
*/
int tty_insert_flip_string_flags(struct tty_port *port,
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(port, goal);
struct tty_buffer *tb = port->buf.tail;
if (unlikely(space == 0))
break;
memcpy(char_buf_ptr(tb, tb->used), chars, space);
memcpy(flag_buf_ptr(tb, 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
* @port: tty port 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.
*/
void tty_schedule_flip(struct tty_port *port)
{
struct tty_bufhead *buf = &port->buf;
/* paired w/ acquire in flush_to_ldisc(); ensures
* flush_to_ldisc() sees buffer data.
*/
smp_store_release(&buf->tail->commit, buf->tail->used);
queue_work(system_unbound_wq, &buf->work);
}
EXPORT_SYMBOL(tty_schedule_flip);
/**
* tty_prepare_flip_string - make room for characters
* @port: tty port
* @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!
*/
int tty_prepare_flip_string(struct tty_port *port, unsigned char **chars,
size_t size)
{
int space = __tty_buffer_request_room(port, size, TTYB_NORMAL);
if (likely(space)) {
struct tty_buffer *tb = port->buf.tail;
*chars = char_buf_ptr(tb, tb->used);
if (~tb->flags & TTYB_NORMAL)
memset(flag_buf_ptr(tb, tb->used), TTY_NORMAL, space);
tb->used += space;
}
return space;
}
EXPORT_SYMBOL_GPL(tty_prepare_flip_string);
static int
receive_buf(struct tty_struct *tty, struct tty_buffer *head, int count)
{
struct tty_ldisc *disc = tty->ldisc;
unsigned char *p = char_buf_ptr(head, head->read);
char *f = NULL;
if (~head->flags & TTYB_NORMAL)
f = flag_buf_ptr(head, head->read);
if (disc->ops->receive_buf2)
count = disc->ops->receive_buf2(tty, p, f, count);
else {
count = min_t(int, count, tty->receive_room);
if (count && disc->ops->receive_buf)
disc->ops->receive_buf(tty, p, f, count);
}
return count;
}
/**
* 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.
*
* The receive_buf method is single threaded for each tty instance.
*
* Locking: takes buffer lock to ensure single-threaded flip buffer
* 'consumer'
*/
static void flush_to_ldisc(struct work_struct *work)
{
struct tty_port *port = container_of(work, struct tty_port, buf.work);
struct tty_bufhead *buf = &port->buf;
struct tty_struct *tty;
struct tty_ldisc *disc;
tty = READ_ONCE(port->itty);
if (tty == NULL)
return;
disc = tty_ldisc_ref(tty);
if (disc == NULL)
return;
mutex_lock(&buf->lock);
while (1) {
struct tty_buffer *head = buf->head;
struct tty_buffer *next;
int count;
/* Ldisc or user is trying to gain exclusive access */
if (atomic_read(&buf->priority))
break;
/* paired w/ release in __tty_buffer_request_room();
* ensures commit value read is not stale if the head
* is advancing to the next buffer
*/
next = smp_load_acquire(&head->next);
/* paired w/ release in __tty_buffer_request_room() or in
* tty_buffer_flush(); ensures we see the committed buffer data
*/
count = smp_load_acquire(&head->commit) - head->read;
if (!count) {
if (next == NULL) {
check_other_closed(tty);
break;
}
buf->head = next;
tty_buffer_free(port, head);
continue;
}
count = receive_buf(tty, head, count);
if (!count)
break;
head->read += count;
}
mutex_unlock(&buf->lock);
tty_ldisc_deref(disc);
}
/**
* tty_flip_buffer_push - terminal
* @port: tty port to push
*
* Queue a push of the terminal flip buffers to the line discipline.
* Can be called from IRQ/atomic context.
*
* In the event of the queue being busy for flipping the work will be
* held off and retried later.
*/
void tty_flip_buffer_push(struct tty_port *port)
{
tty_schedule_flip(port);
}
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.
*/
void tty_buffer_init(struct tty_port *port)
{
struct tty_bufhead *buf = &port->buf;
mutex_init(&buf->lock);
tty_buffer_reset(&buf->sentinel, 0);
buf->head = &buf->sentinel;
buf->tail = &buf->sentinel;
init_llist_head(&buf->free);
atomic_set(&buf->mem_used, 0);
atomic_set(&buf->priority, 0);
INIT_WORK(&buf->work, flush_to_ldisc);
buf->mem_limit = TTYB_DEFAULT_MEM_LIMIT;
}
/**
* tty_buffer_set_limit - change the tty buffer memory limit
* @port: tty port to change
*
* Change the tty buffer memory limit.
* Must be called before the other tty buffer functions are used.
*/
int tty_buffer_set_limit(struct tty_port *port, int limit)
{
if (limit < MIN_TTYB_SIZE)
return -EINVAL;
port->buf.mem_limit = limit;
return 0;
}
EXPORT_SYMBOL_GPL(tty_buffer_set_limit);
/* slave ptys can claim nested buffer lock when handling BRK and INTR */
void tty_buffer_set_lock_subclass(struct tty_port *port)
{
lockdep_set_subclass(&port->buf.lock, TTY_LOCK_SLAVE);
}
bool tty_buffer_restart_work(struct tty_port *port)
{
return queue_work(system_unbound_wq, &port->buf.work);
}
bool tty_buffer_cancel_work(struct tty_port *port)
{
return cancel_work_sync(&port->buf.work);
}
