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ebee41c849
We are used to handle "bad" states in the 'if's in the kernel. Refactor (invert the two conditions in) __tty_buffer_request_room(), so that the code returns from the fast paths immediately instead of postponing to the heavy end of the function. Signed-off-by: "Jiri Slaby (SUSE)" <jirislaby@kernel.org> Link: https://lore.kernel.org/r/20230816105530.3335-11-jirislaby@kernel.org Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
629 lines
16 KiB
C
629 lines
16 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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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/minmax.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/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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#include "tty.h"
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#define MIN_TTYB_SIZE 256
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#define TTYB_ALIGN_MASK 0xff
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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_DEFAULT_MEM_LIMIT (640 * 1024UL)
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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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* 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) & ~TTYB_ALIGN_MASK)
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/**
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* tty_buffer_lock_exclusive - gain exclusive access to buffer
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* @port: tty port owning the flip buffer
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*
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* Guarantees safe use of the &tty_ldisc_ops.receive_buf() method by excluding
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* the buffer work and any pending flush from using the flip buffer. Data can
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* continue to be added concurrently to the flip buffer from the driver side.
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*
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* See also tty_buffer_unlock_exclusive().
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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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EXPORT_SYMBOL_GPL(tty_buffer_lock_exclusive);
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/**
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* tty_buffer_unlock_exclusive - release exclusive access
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* @port: tty port owning the flip buffer
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*
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* The buffer work is restarted if there is data in the flip buffer.
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*
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* See also tty_buffer_lock_exclusive().
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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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EXPORT_SYMBOL_GPL(tty_buffer_unlock_exclusive);
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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 reaching
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* the buffer limit.
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*
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* Note: this does not guarantee that memory is available to write the returned
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* # of bytes (use tty_prepare_flip_string() to pre-allocate if memory
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* guarantee is required).
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*/
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unsigned int tty_buffer_space_avail(struct tty_port *port)
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{
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int space = port->buf.mem_limit - atomic_read(&port->buf.mem_used);
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return max(space, 0);
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}
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EXPORT_SYMBOL_GPL(tty_buffer_space_avail);
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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->lookahead = 0;
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p->read = 0;
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p->flags = true;
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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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* @port: tty port to free from
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*
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* Remove all the buffers pending on a tty whether queued with data or in the
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* 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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unsigned int freed = 0;
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int still_used;
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while ((p = buf->head) != NULL) {
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buf->head = p->next;
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freed += p->size;
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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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still_used = atomic_xchg(&buf->mem_used, 0);
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WARN(still_used != freed, "we still have not freed %d bytes!",
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still_used - freed);
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}
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/**
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* tty_buffer_alloc - allocate a tty buffer
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* @port: tty port
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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. We
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* round our buffers off in 256 character chunks to get better allocation
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* behaviour.
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*
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* Returns: %NULL if out of memory or the allocation would exceed the per
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* 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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*/
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if (atomic_read(&port->buf.mem_used) > port->buf.mem_limit)
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return NULL;
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p = kmalloc(struct_size(p, data, 2 * size), GFP_ATOMIC | __GFP_NOWARN);
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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.mem_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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* @port: tty port 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 internal
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* 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->mem_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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* @ld: optional ldisc ptr (must be referenced)
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*
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* Flush all the buffers containing receive data. If @ld != %NULL, flush the
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* ldisc input buffer.
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*
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* Locking: takes buffer lock to ensure single-threaded flip buffer 'consumer'.
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*/
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void tty_buffer_flush(struct tty_struct *tty, struct tty_ldisc *ld)
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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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/* paired w/ release in __tty_buffer_request_room; ensures there are
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* no pending memory accesses to the freed buffer
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*/
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while ((next = smp_load_acquire(&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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buf->head->lookahead = buf->head->read;
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if (ld && ld->ops->flush_buffer)
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ld->ops->flush_buffer(tty);
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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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* @port: tty port
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* @size: size desired
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* @flags: buffer has to store flags along character data
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*
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* Make at least @size bytes of linear space available for the tty buffer.
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*
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* Will change over to a new buffer if the current buffer is encoded as
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* %TTY_NORMAL (so has no flags buffer) and the new buffer requires a flags
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* buffer.
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*
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* Returns: the size we managed to find.
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*/
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static int __tty_buffer_request_room(struct tty_port *port, size_t size,
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bool flags)
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{
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struct tty_bufhead *buf = &port->buf;
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struct tty_buffer *n, *b = buf->tail;
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size_t left = (b->flags ? 1 : 2) * b->size - b->used;
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bool change = !b->flags && flags;
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if (!change && left >= size)
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return size;
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/* This is the slow path - looking for new buffers to use */
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n = tty_buffer_alloc(port, size);
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if (n == NULL)
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return change ? 0 : left;
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n->flags = flags;
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buf->tail = n;
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/*
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* Paired w/ acquire in flush_to_ldisc() and lookahead_bufs()
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* ensures they see all buffer data.
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*/
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smp_store_release(&b->commit, b->used);
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/*
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* Paired w/ acquire in flush_to_ldisc() and lookahead_bufs()
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* ensures the latest commit value can be read before the head
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* is advanced to the next buffer.
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*/
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smp_store_release(&b->next, n);
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return size;
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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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return __tty_buffer_request_room(port, size, true);
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}
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EXPORT_SYMBOL_GPL(tty_buffer_request_room);
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size_t __tty_insert_flip_string_flags(struct tty_port *port, const u8 *chars,
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const u8 *flags, bool mutable_flags,
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size_t size)
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{
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bool need_flags = mutable_flags || flags[0] != TTY_NORMAL;
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size_t copied = 0;
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do {
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size_t goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
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size_t space = __tty_buffer_request_room(port, goal, need_flags);
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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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if (mutable_flags) {
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memcpy(flag_buf_ptr(tb, tb->used), flags, space);
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flags += space;
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} else if (tb->flags) {
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memset(flag_buf_ptr(tb, tb->used), flags[0], space);
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} else {
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/* tb->flags should be available once requested */
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WARN_ON_ONCE(need_flags);
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}
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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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*/
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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_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.
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*
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* This is used for drivers that need their own block copy routines into the
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* buffer. There is no guarantee the buffer is a DMA target!
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*
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* Returns: the length available and buffer pointer (@chars) to the space which
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* is now allocated and accounted for as ready for normal characters.
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*/
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size_t tty_prepare_flip_string(struct tty_port *port, u8 **chars, size_t size)
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{
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size_t space = __tty_buffer_request_room(port, size, false);
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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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if (tb->flags)
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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_ldisc_receive_buf - forward data to line discipline
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* @ld: line discipline to process input
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* @p: char buffer
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* @f: %TTY_NORMAL, %TTY_BREAK, etc. flags buffer
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* @count: number of bytes to process
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*
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* Callers other than flush_to_ldisc() need to exclude the kworker from
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* concurrent use of the line discipline, see paste_selection().
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*
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* Returns: the number of bytes processed.
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*/
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size_t tty_ldisc_receive_buf(struct tty_ldisc *ld, const u8 *p, const u8 *f,
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size_t count)
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{
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if (ld->ops->receive_buf2)
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count = ld->ops->receive_buf2(ld->tty, p, f, count);
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else {
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count = min_t(size_t, count, ld->tty->receive_room);
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if (count && ld->ops->receive_buf)
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ld->ops->receive_buf(ld->tty, p, f, count);
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}
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return count;
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}
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EXPORT_SYMBOL_GPL(tty_ldisc_receive_buf);
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static void lookahead_bufs(struct tty_port *port, struct tty_buffer *head)
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{
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head->lookahead = max(head->lookahead, head->read);
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while (head) {
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struct tty_buffer *next;
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unsigned int count;
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/*
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* Paired w/ release in __tty_buffer_request_room();
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* ensures commit value read is not stale if the head
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* is advancing to the next buffer.
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*/
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next = smp_load_acquire(&head->next);
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/*
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* Paired w/ release in __tty_buffer_request_room() or in
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* tty_buffer_flush(); ensures we see the committed buffer data.
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*/
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count = smp_load_acquire(&head->commit) - head->lookahead;
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if (!count) {
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head = next;
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continue;
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}
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if (port->client_ops->lookahead_buf) {
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u8 *p, *f = NULL;
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p = char_buf_ptr(head, head->lookahead);
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if (head->flags)
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f = flag_buf_ptr(head, head->lookahead);
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port->client_ops->lookahead_buf(port, p, f, count);
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}
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head->lookahead += count;
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}
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}
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static size_t
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receive_buf(struct tty_port *port, struct tty_buffer *head, size_t count)
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{
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u8 *p = char_buf_ptr(head, head->read);
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const u8 *f = NULL;
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size_t n;
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if (head->flags)
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f = flag_buf_ptr(head, head->read);
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n = port->client_ops->receive_buf(port, p, f, count);
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if (n > 0)
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memset(p, 0, n);
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return n;
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}
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/**
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* flush_to_ldisc - flush data from buffer 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 from the
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* 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 '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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mutex_lock(&buf->lock);
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while (1) {
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struct tty_buffer *head = buf->head;
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struct tty_buffer *next;
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size_t count, rcvd;
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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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/* paired w/ release in __tty_buffer_request_room();
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* ensures commit value read is not stale if the head
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* is advancing to the next buffer
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*/
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next = smp_load_acquire(&head->next);
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/* paired w/ release in __tty_buffer_request_room() or in
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* tty_buffer_flush(); ensures we see the committed buffer data
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*/
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count = smp_load_acquire(&head->commit) - head->read;
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if (!count) {
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if (next == NULL)
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break;
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buf->head = next;
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tty_buffer_free(port, head);
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continue;
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}
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rcvd = receive_buf(port, head, count);
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head->read += rcvd;
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if (rcvd < count)
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lookahead_bufs(port, head);
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if (!rcvd)
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break;
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if (need_resched())
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cond_resched();
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}
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mutex_unlock(&buf->lock);
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}
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static inline void tty_flip_buffer_commit(struct tty_buffer *tail)
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{
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/*
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* Paired w/ acquire in flush_to_ldisc(); ensures flush_to_ldisc() sees
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* buffer data.
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*/
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smp_store_release(&tail->commit, tail->used);
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}
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|
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/**
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* tty_flip_buffer_push - push terminal buffers
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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. Can be
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* called from IRQ/atomic context.
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*
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* In the event of the queue being busy for flipping the work will be held off
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* 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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|
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tty_flip_buffer_commit(buf->tail);
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queue_work(system_unbound_wq, &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_insert_flip_string_and_push_buffer - add characters to the tty buffer and
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|
* push
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|
* @port: tty port
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|
* @chars: characters
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|
* @size: size
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|
*
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* The function combines tty_insert_flip_string() and tty_flip_buffer_push()
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|
* with the exception of properly holding the @port->lock.
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|
*
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|
* To be used only internally (by pty currently).
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|
*
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* Returns: the number added.
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|
*/
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|
int tty_insert_flip_string_and_push_buffer(struct tty_port *port,
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|
const u8 *chars, size_t size)
|
|
{
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|
struct tty_bufhead *buf = &port->buf;
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|
unsigned long flags;
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|
|
|
spin_lock_irqsave(&port->lock, flags);
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size = tty_insert_flip_string(port, chars, size);
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|
if (size)
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|
tty_flip_buffer_commit(buf->tail);
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|
spin_unlock_irqrestore(&port->lock, flags);
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|
|
|
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);
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|
tty_buffer_reset(&buf->sentinel, 0);
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|
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);
|
|
}
|