Use a 0-sized sentinel to avoid assigning the head ptr from
the driver side thread. This also eliminates testing head/tail
for NULL.
When the sentinel is first 'consumed' by the buffer work
(or by tty_buffer_flush()), it is detached from the list but not
freed nor added to the free list. Both buffer work and
tty_buffer_flush() continue to preserve at least 1 flip buffer
to which head & tail is pointed.
Signed-off-by: Peter Hurley <peter@xxxxxxxxxxxxxxxxxx>
---
drivers/tty/tty_buffer.c | 49 ++++++++++++++++++------------------------------
include/linux/tty.h | 1 +
2 files changed, 19 insertions(+), 31 deletions(-)
diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
index 069640e..231b7a8 100644
--- a/drivers/tty/tty_buffer.c
+++ b/drivers/tty/tty_buffer.c
@@ -49,13 +49,16 @@ void tty_buffer_free_all(struct tty_port *port)
while ((p = buf->head) != NULL) {
buf->head = p->next;
- kfree(p);
+ if (p->size > 0)
+ kfree(p);
}
llist = llist_del_all(&buf->free);
llist_for_each_entry_safe(p, next, llist, free)
kfree(p);
- buf->tail = NULL;
+ tty_buffer_reset(&buf->sentinel, 0);
+ buf->head = &buf->sentinel;
+ buf->tail = &buf->sentinel;
buf->memory_used = 0;
}
@@ -120,7 +123,7 @@ static void tty_buffer_free(struct tty_port *port, struct tty_buffer *b)
if (b->size > MIN_TTYB_SIZE)
kfree(b);
- else
+ else if (b->size > 0)
llist_add(&b->free, &buf->free);
}
@@ -140,8 +143,6 @@ static void __tty_buffer_flush(struct tty_port *port)
struct tty_bufhead *buf = &port->buf;
struct tty_buffer *next;
- if (unlikely(buf->head == NULL))
- return;
while ((next = buf->head->next) != NULL) {
tty_buffer_free(port, buf->head);
buf->head = next;
@@ -200,23 +201,14 @@ int tty_buffer_request_room(struct tty_port *port, size_t size)
int left;
unsigned long flags;
spin_lock_irqsave(&buf->lock, flags);
- /* OPTIMISATION: We could keep a per tty "zero" sized buffer to
- remove this conditional if its worth it. This would be invisible
- to the callers */
b = buf->tail;
- if (b != NULL)
- left = b->size - b->used;
- else
- left = 0;
+ left = b->size - b->used;
if (left < size) {
/* This is the slow path - looking for new buffers to use */
if ((n = tty_buffer_alloc(port, size)) != NULL) {
- if (b != NULL) {
- b->next = n;
- b->commit = b->used;
- } else
- buf->head = n;
+ b->next = n;
+ b->commit = b->used;
buf->tail = n;
} else
size = left;
@@ -247,10 +239,8 @@ int tty_insert_flip_string_fixed_flag(struct tty_port *port,
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 there is no space then tb may be NULL */
- if (unlikely(space == 0)) {
+ if (unlikely(space == 0))
break;
- }
memcpy(char_buf_ptr(tb, tb->used), chars, space);
memset(flag_buf_ptr(tb, tb->used), flag, space);
tb->used += space;
@@ -285,10 +275,8 @@ int tty_insert_flip_string_flags(struct tty_port *port,
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 there is no space then tb may be NULL */
- if (unlikely(space == 0)) {
+ 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;
@@ -322,8 +310,7 @@ void tty_schedule_flip(struct tty_port *port)
WARN_ON(port->low_latency);
spin_lock_irqsave(&buf->lock, flags);
- if (buf->tail != NULL)
- buf->tail->commit = buf->tail->used;
+ buf->tail->commit = buf->tail->used;
spin_unlock_irqrestore(&buf->lock, flags);
schedule_work(&buf->work);
}
@@ -438,8 +425,8 @@ static void flush_to_ldisc(struct work_struct *work)
spin_lock_irqsave(&buf->lock, flags);
if (!test_and_set_bit(TTYP_FLUSHING, &port->iflags)) {
- struct tty_buffer *head;
- while ((head = buf->head) != NULL) {
+ while (1) {
+ struct tty_buffer *head = buf->head;
int count;
count = head->commit - head->read;
@@ -509,8 +496,7 @@ void tty_flip_buffer_push(struct tty_port *port)
unsigned long flags;
spin_lock_irqsave(&buf->lock, flags);
- if (buf->tail != NULL)
- buf->tail->commit = buf->tail->used;
+ buf->tail->commit = buf->tail->used;
spin_unlock_irqrestore(&buf->lock, flags);
if (port->low_latency)
@@ -535,8 +521,9 @@ void tty_buffer_init(struct tty_port *port)
struct tty_bufhead *buf = &port->buf;
spin_lock_init(&buf->lock);
- buf->head = NULL;
- buf->tail = NULL;
+ tty_buffer_reset(&buf->sentinel, 0);
+ buf->head = &buf->sentinel;
+ buf->tail = &buf->sentinel;
init_llist_head(&buf->free);
buf->memory_used = 0;
INIT_WORK(&buf->work, flush_to_ldisc);
diff --git a/include/linux/tty.h b/include/linux/tty.h
index 5043b12..2e93eb8 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -67,6 +67,7 @@ static inline char *flag_buf_ptr(struct tty_buffer *b, int ofs)
struct tty_bufhead {
struct work_struct work;
spinlock_t lock;
+ struct tty_buffer sentinel;
struct tty_buffer *head; /* Queue head */
struct tty_buffer *tail; /* Active buffer */
struct llist_head free; /* Free queue head */
--
1.8.1.2
--
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