// 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_buffer.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; bool restart = buf->head->commit != buf->head->read; atomic_dec(&buf->priority); mutex_unlock(&buf->lock); if (restart) queue_work(system_dfl_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(struct_size(p, data, 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 *n, *b = buf->tail; size_t left = (b->flags ? 1 : 2) * b->size - b->used; bool change = !b->flags && flags; if (!change && left >= size) return size; /* This is the slow path - looking for new buffers to use */ n = tty_buffer_alloc(port, size); if (n == NULL) return change ? 0 : left; 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); 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); size_t __tty_insert_flip_string_flags(struct tty_port *port, const u8 *chars, const u8 *flags, bool mutable_flags, size_t size){ bool need_flags = mutable_flags || flags[0] != TTY_NORMAL; size_t copied = 0; do { size_t goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE); size_t space = __tty_buffer_request_room(port, goal, need_flags); struct tty_buffer *tb = port->buf.tail; if (unlikely(space == 0)) break; memcpy(char_buf_ptr(tb, tb->used), chars, space); if (mutable_flags) { memcpy(flag_buf_ptr(tb, tb->used), flags, space); flags += space; } else if (tb->flags) { memset(flag_buf_ptr(tb, tb->used), flags[0], space); } else { /* tb->flags should be available once requested */ WARN_ON_ONCE(need_flags); } 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_flags); /** * 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. */size_t tty_prepare_flip_string(struct tty_port *port, u8 **chars, size_t size){ size_t 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. */size_t tty_ldisc_receive_buf(struct tty_ldisc *ld, const u8 *p, const u8 *f, size_t count){ if (ld->ops->receive_buf2) count = ld->ops->receive_buf2(ld->tty, p, f, count); else { count = min_t(size_t, 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) { u8 *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 size_treceive_buf(struct tty_port *port, struct tty_buffer *head, size_t count){ u8 *p = char_buf_ptr(head, head->read); const u8 *f = NULL; size_t 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; size_t 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;Lines 1–500 of 627. 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// 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_buffer.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; bool restart = buf->head->commit != buf->head->read; atomic_dec(&buf->priority); mutex_unlock(&buf->lock); if (restart) queue_work(system_dfl_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(struct_size(p, data, 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 *n, *b = buf->tail; size_t left = (b->flags ? 1 : 2) * b->size - b->used; bool change = !b->flags && flags; if (!change && left >= size) return size; /* This is the slow path - looking for new buffers to use */ n = tty_buffer_alloc(port, size); if (n == NULL) return change ? 0 : left; 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); 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); size_t __tty_insert_flip_string_flags(struct tty_port *port, const u8 *chars, const u8 *flags, bool mutable_flags, size_t size) { bool need_flags = mutable_flags || flags[0] != TTY_NORMAL; size_t copied = 0; do { size_t goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE); size_t space = __tty_buffer_request_room(port, goal, need_flags); struct tty_buffer *tb = port->buf.tail; if (unlikely(space == 0)) break; memcpy(char_buf_ptr(tb, tb->used), chars, space); if (mutable_flags) { memcpy(flag_buf_ptr(tb, tb->used), flags, space); flags += space; } else if (tb->flags) { memset(flag_buf_ptr(tb, tb->used), flags[0], space); } else { /* tb->flags should be available once requested */ WARN_ON_ONCE(need_flags); } 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_flags); /** * 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. */ size_t tty_prepare_flip_string(struct tty_port *port, u8 **chars, size_t size) { size_t 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. */ size_t tty_ldisc_receive_buf(struct tty_ldisc *ld, const u8 *p, const u8 *f, size_t count) { if (ld->ops->receive_buf2) count = ld->ops->receive_buf2(ld->tty, p, f, count); else { count = min_t(size_t, 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) { u8 *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 size_t receive_buf(struct tty_port *port, struct tty_buffer *head, size_t count) { u8 *p = char_buf_ptr(head, head->read); const u8 *f = NULL; size_t 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; size_t 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;