From da261e7fe7b0e23a0d4d46039d20dc60fa197b49 Mon Sep 17 00:00:00 2001 From: Peter Hurley Date: Sat, 15 Jun 2013 09:14:14 -0400 Subject: [PATCH] tty: Simplify tty buffer/ldisc interface with helper function Ldisc interface functions must be called with interrupts enabled. Separating the ldisc calls into a helper function simplies the eventual removal of the spinlock. Note that access to the buf->head ptr outside the spinlock is safe here because; * __tty_buffer_flush() is prevented from running while buffer work performs i/o, * tty_buffer_find() only assigns buf->head if the flip buffer list is empty (which is never the case in flush_to_ldisc() since at least one buffer is always left in the list after use) Access to the read index outside the spinlock is safe here for the same reasons. Update the buffer's read index _after_ the data has been received by the ldisc. Signed-off-by: Peter Hurley Signed-off-by: Greg Kroah-Hartman --- drivers/tty/tty_buffer.c | 29 +++++++++++++++++------------ 1 file changed, 17 insertions(+), 12 deletions(-) diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c index a42a028a9d4e..6c7a1d043c76 100644 --- a/drivers/tty/tty_buffer.c +++ b/drivers/tty/tty_buffer.c @@ -403,6 +403,18 @@ int tty_prepare_flip_string_flags(struct tty_port *port, EXPORT_SYMBOL_GPL(tty_prepare_flip_string_flags); +static int +receive_buf(struct tty_struct *tty, struct tty_buffer *head, int count) +{ + struct tty_ldisc *disc = tty->ldisc; + + count = min_t(int, count, tty->receive_room); + if (count) + disc->ops->receive_buf(tty, head->char_buf_ptr + head->read, + head->flag_buf_ptr + head->read, count); + head->read += count; + return count; +} /** * flush_to_ldisc @@ -438,8 +450,6 @@ static void flush_to_ldisc(struct work_struct *work) struct tty_buffer *head; while ((head = buf->head) != NULL) { int count; - char *char_buf; - unsigned char *flag_buf; count = head->commit - head->read; if (!count) { @@ -449,16 +459,10 @@ static void flush_to_ldisc(struct work_struct *work) tty_buffer_free(port, head); continue; } - if (!tty->receive_room) - break; - if (count > tty->receive_room) - count = tty->receive_room; - char_buf = head->char_buf_ptr + head->read; - flag_buf = head->flag_buf_ptr + head->read; - head->read += count; spin_unlock_irqrestore(&buf->lock, flags); - disc->ops->receive_buf(tty, char_buf, - flag_buf, count); + + count = receive_buf(tty, head, count); + spin_lock_irqsave(&buf->lock, flags); /* Ldisc or user is trying to flush the buffers. We may have a deferred request to flush the @@ -469,7 +473,8 @@ static void flush_to_ldisc(struct work_struct *work) clear_bit(TTYP_FLUSHPENDING, &port->iflags); wake_up(&tty->read_wait); break; - } + } else if (!count) + break; } clear_bit(TTYP_FLUSHING, &port->iflags); } -- 2.20.1