linux/drivers/tty/tty_buffer.c
Ilpo Järvinen 2e2b4b8961 tty: Convert tty_buffer flags to bool
The struct tty_buffer has flags which is only used for storing TTYB_NORMAL.
There is also a few quite confusing operations for checking the presense
of TTYB_NORMAL. Simplify things by converting flags to bool.

Despite the name remaining the same, the meaning of "flags" is altered
slightly by this change. Previously it referred to flags of the buffer
(only TTYB_NORMAL being used as a flag). After this change, flags tell
whether the buffer contains/should be allocated with flags array along
with character data array. It is much more suitable name that
TTYB_NORMAL was for this purpose, thus the name remains.

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20221019105504.16800-1-ilpo.jarvinen@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2022-11-09 13:02:16 +01:00

699 lines
18 KiB
C

// SPDX-License-Identifier: GPL-2.0
/*
* Tty buffer allocation management
*/
#include <linux/types.h>
#include <linux/errno.h>
#include <linux/minmax.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>
#include "tty.h"
#define MIN_TTYB_SIZE 256
#define TTYB_ALIGN_MASK 0xff
/*
* Byte threshold to limit memory consumption for flip buffers.
* The actual memory limit is > 2x this amount.
*/
#define TTYB_DEFAULT_MEM_LIMIT (640 * 1024UL)
/*
* 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
* 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) & ~TTYB_ALIGN_MASK)
/**
* tty_buffer_lock_exclusive - gain exclusive access to buffer
* @port: tty port owning the flip buffer
*
* Guarantees safe use of the &tty_ldisc_ops.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.
*
* See also tty_buffer_unlock_exclusive().
*/
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);
/**
* tty_buffer_unlock_exclusive - release exclusive access
* @port: tty port owning the flip buffer
*
* The buffer work is restarted if there is data in the flip buffer.
*
* See also 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() to pre-allocate if memory
* guarantee is required).
*/
unsigned 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->lookahead = 0;
p->read = 0;
p->flags = true;
}
/**
* tty_buffer_free_all - free buffers used by a tty
* @port: tty port 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;
unsigned int freed = 0;
int still_used;
while ((p = buf->head) != NULL) {
buf->head = p->next;
freed += p->size;
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;
still_used = atomic_xchg(&buf->mem_used, 0);
WARN(still_used != freed, "we still have not freed %d bytes!",
still_used - freed);
}
/**
* tty_buffer_alloc - allocate a tty buffer
* @port: tty port
* @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.
*
* Returns: %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 | __GFP_NOWARN);
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
* @port: tty port 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;
buf->head->lookahead = buf->head->read;
if (ld && ld->ops->flush_buffer)
ld->ops->flush_buffer(tty);
atomic_dec(&buf->priority);
mutex_unlock(&buf->lock);
}
/**
* __tty_buffer_request_room - grow tty buffer if needed
* @port: tty port
* @size: size desired
* @flags: buffer has to store flags along character data
*
* Make at least @size bytes of linear space available for the tty buffer.
*
* 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.
*
* Returns: the size we managed to find.
*/
static int __tty_buffer_request_room(struct tty_port *port, size_t size,
bool flags)
{
struct tty_bufhead *buf = &port->buf;
struct tty_buffer *b, *n;
int left, change;
b = buf->tail;
if (!b->flags)
left = 2 * b->size - b->used;
else
left = b->size - b->used;
change = !b->flags && flags;
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() and lookahead_bufs()
* ensures they see all buffer data.
*/
smp_store_release(&b->commit, b->used);
/*
* Paired w/ acquire in flush_to_ldisc() and lookahead_bufs()
* 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, true);
}
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;
bool flags = flag != TTY_NORMAL;
do {
int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
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)
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_insert_flip_char - add one character to the tty buffer
* @port: tty port
* @ch: character
* @flag: flag byte
*
* Queue a single byte @ch to the tty buffering, with an optional flag. This is
* the slow path of tty_insert_flip_char().
*/
int __tty_insert_flip_char(struct tty_port *port, unsigned char ch, char flag)
{
struct tty_buffer *tb;
bool flags = flag != TTY_NORMAL;
if (!__tty_buffer_request_room(port, 1, flags))
return 0;
tb = port->buf.tail;
if (tb->flags)
*flag_buf_ptr(tb, tb->used) = flag;
*char_buf_ptr(tb, tb->used++) = ch;
return 1;
}
EXPORT_SYMBOL(__tty_insert_flip_char);
/**
* 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.
*
* 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!
*
* Returns: the length available and buffer pointer (@chars) to the space which
* is now allocated and accounted for as ready for normal characters.
*/
int tty_prepare_flip_string(struct tty_port *port, unsigned char **chars,
size_t size)
{
int space = __tty_buffer_request_room(port, size, false);
if (likely(space)) {
struct tty_buffer *tb = port->buf.tail;
*chars = char_buf_ptr(tb, tb->used);
if (tb->flags)
memset(flag_buf_ptr(tb, tb->used), TTY_NORMAL, space);
tb->used += space;
}
return space;
}
EXPORT_SYMBOL_GPL(tty_prepare_flip_string);
/**
* tty_ldisc_receive_buf - forward data to line discipline
* @ld: line discipline to process input
* @p: char buffer
* @f: %TTY_NORMAL, %TTY_BREAK, etc. flags buffer
* @count: number of bytes to process
*
* Callers other than flush_to_ldisc() need to exclude the kworker from
* concurrent use of the line discipline, see paste_selection().
*
* Returns: the number of bytes processed.
*/
int tty_ldisc_receive_buf(struct tty_ldisc *ld, const unsigned char *p,
const char *f, int count)
{
if (ld->ops->receive_buf2)
count = ld->ops->receive_buf2(ld->tty, p, f, count);
else {
count = min_t(int, count, ld->tty->receive_room);
if (count && ld->ops->receive_buf)
ld->ops->receive_buf(ld->tty, p, f, count);
}
return count;
}
EXPORT_SYMBOL_GPL(tty_ldisc_receive_buf);
static void lookahead_bufs(struct tty_port *port, struct tty_buffer *head)
{
head->lookahead = max(head->lookahead, head->read);
while (head) {
struct tty_buffer *next;
unsigned int count;
/*
* 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->lookahead;
if (!count) {
head = next;
continue;
}
if (port->client_ops->lookahead_buf) {
unsigned char *p, *f = NULL;
p = char_buf_ptr(head, head->lookahead);
if (head->flags)
f = flag_buf_ptr(head, head->lookahead);
port->client_ops->lookahead_buf(port, p, f, count);
}
head->lookahead += count;
}
}
static int
receive_buf(struct tty_port *port, struct tty_buffer *head, int count)
{
unsigned char *p = char_buf_ptr(head, head->read);
const char *f = NULL;
int n;
if (head->flags)
f = flag_buf_ptr(head, head->read);
n = port->client_ops->receive_buf(port, p, f, count);
if (n > 0)
memset(p, 0, n);
return n;
}
/**
* flush_to_ldisc - flush data from buffer 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;
mutex_lock(&buf->lock);
while (1) {
struct tty_buffer *head = buf->head;
struct tty_buffer *next;
int count, rcvd;
/* 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)
break;
buf->head = next;
tty_buffer_free(port, head);
continue;
}
rcvd = receive_buf(port, head, count);
head->read += rcvd;
if (rcvd < count)
lookahead_bufs(port, head);
if (!rcvd)
break;
if (need_resched())
cond_resched();
}
mutex_unlock(&buf->lock);
}
static inline void tty_flip_buffer_commit(struct tty_buffer *tail)
{
/*
* Paired w/ acquire in flush_to_ldisc(); ensures flush_to_ldisc() sees
* buffer data.
*/
smp_store_release(&tail->commit, tail->used);
}
/**
* tty_flip_buffer_push - push terminal buffers
* @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)
{
struct tty_bufhead *buf = &port->buf;
tty_flip_buffer_commit(buf->tail);
queue_work(system_unbound_wq, &buf->work);
}
EXPORT_SYMBOL(tty_flip_buffer_push);
/**
* tty_insert_flip_string_and_push_buffer - add characters to the tty buffer and
* push
* @port: tty port
* @chars: characters
* @size: size
*
* The function combines tty_insert_flip_string() and tty_flip_buffer_push()
* with the exception of properly holding the @port->lock.
*
* To be used only internally (by pty currently).
*
* Returns: the number added.
*/
int tty_insert_flip_string_and_push_buffer(struct tty_port *port,
const unsigned char *chars, size_t size)
{
struct tty_bufhead *buf = &port->buf;
unsigned long flags;
spin_lock_irqsave(&port->lock, flags);
size = tty_insert_flip_string(port, chars, size);
if (size)
tty_flip_buffer_commit(buf->tail);
spin_unlock_irqrestore(&port->lock, flags);
queue_work(system_unbound_wq, &buf->work);
return size;
}
/**
* tty_buffer_init - prepare a tty buffer structure
* @port: tty port 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
* @limit: memory limit to set
*
* 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);
}
void tty_buffer_flush_work(struct tty_port *port)
{
flush_work(&port->buf.work);
}