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 <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
index a42a028..6c7a1d0 100644
--- a/drivers/tty/tty_buffer.c
+++ b/drivers/tty/tty_buffer.c
@@ -403,6 +403,18 @@
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 @@
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 @@
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 @@
clear_bit(TTYP_FLUSHPENDING, &port->iflags);
wake_up(&tty->read_wait);
break;
- }
+ } else if (!count)
+ break;
}
clear_bit(TTYP_FLUSHING, &port->iflags);
}