1 files changed, 41 insertions, 19 deletions

diff --git a/drivers/tty/n_hdlc.c b/drivers/tty/n_hdlc.c
index 12557ee1edb6..1363e659dc1d 100644
--- a/drivers/tty/n_hdlc.c
+++ b/drivers/tty/n_hdlc.c
@@ -416,13 +416,19 @@ static void n_hdlc_tty_receive(struct tty_struct *tty, const __u8 *data,
  * Returns the number of bytes returned or error code.
  */
 static ssize_t n_hdlc_tty_read(struct tty_struct *tty, struct file *file,
-			   __u8 __user *buf, size_t nr)
+			   __u8 *kbuf, size_t nr,
+			   void **cookie, unsigned long offset)
 {
 	struct n_hdlc *n_hdlc = tty->disc_data;
 	int ret = 0;
 	struct n_hdlc_buf *rbuf;
 	DECLARE_WAITQUEUE(wait, current);
 
+	/* Is this a repeated call for an rbuf we already found earlier? */
+	rbuf = *cookie;
+	if (rbuf)
+		goto have_rbuf;
+
 	add_wait_queue(&tty->read_wait, &wait);
 
 	for (;;) {
@@ -436,25 +442,8 @@ static ssize_t n_hdlc_tty_read(struct tty_struct *tty, struct file *file,
 		set_current_state(TASK_INTERRUPTIBLE);
 
 		rbuf = n_hdlc_buf_get(&n_hdlc->rx_buf_list);
-		if (rbuf) {
-			if (rbuf->count > nr) {
-				/* too large for caller's buffer */
-				ret = -EOVERFLOW;
-			} else {
-				__set_current_state(TASK_RUNNING);
-				if (copy_to_user(buf, rbuf->buf, rbuf->count))
-					ret = -EFAULT;
-				else
-					ret = rbuf->count;
-			}
-
-			if (n_hdlc->rx_free_buf_list.count >
-			    DEFAULT_RX_BUF_COUNT)
-				kfree(rbuf);
-			else
-				n_hdlc_buf_put(&n_hdlc->rx_free_buf_list, rbuf);
+		if (rbuf)
 			break;
-		}
 
 		/* no data */
 		if (tty_io_nonblock(tty, file)) {
@@ -473,6 +462,39 @@ static ssize_t n_hdlc_tty_read(struct tty_struct *tty, struct file *file,
 	remove_wait_queue(&tty->read_wait, &wait);
 	__set_current_state(TASK_RUNNING);
 
+	if (!rbuf)
+		return ret;
+	*cookie = rbuf;
+
+have_rbuf:
+	/* Have we used it up entirely? */
+	if (offset >= rbuf->count)
+		goto done_with_rbuf;
+
+	/* More data to go, but can't copy any more? EOVERFLOW */
+	ret = -EOVERFLOW;
+	if (!nr)
+		goto done_with_rbuf;
+
+	/* Copy as much data as possible */
+	ret = rbuf->count - offset;
+	if (ret > nr)
+		ret = nr;
+	memcpy(kbuf, rbuf->buf+offset, ret);
+	offset += ret;
+
+	/* If we still have data left, we leave the rbuf in the cookie */
+	if (offset < rbuf->count)
+		return ret;
+
+done_with_rbuf:
+	*cookie = NULL;
+
+	if (n_hdlc->rx_free_buf_list.count > DEFAULT_RX_BUF_COUNT)
+		kfree(rbuf);
+	else
+		n_hdlc_buf_put(&n_hdlc->rx_free_buf_list, rbuf);
+
 	return ret;
 
 }	/* end of n_hdlc_tty_read() */