tty: make receive_buf() return the amout of bytes received

it makes it simpler to keep track of the amount of
bytes received and simplifies how flush_to_ldisc counts
the remaining bytes. It also fixes a bug of lost bytes
on n_tty when flushing too many bytes via the USB
serial gadget driver.

Tested-by: Stefan Bigler <stefan.bigler@keymile.com>
Tested-by: Toby Gray <toby.gray@realvnc.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 9 insertions, 6 deletions

diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
index f1a7918d71aa..46de2e075dac 100644
--- a/drivers/tty/tty_buffer.c
+++ b/drivers/tty/tty_buffer.c
@@ -416,6 +416,7 @@ static void flush_to_ldisc(struct work_struct *work)
                 struct tty_buffer *head, *tail = tty->buf.tail;
                 int seen_tail = 0;
                 while ((head = tty->buf.head) != NULL) {
+                        int copied;
                         int count;
                         char *char_buf;
                         unsigned char *flag_buf;
@@ -442,17 +443,19 @@ static void flush_to_ldisc(struct work_struct *work)
                            line discipline as we want to empty the queue */
                         if (test_bit(TTY_FLUSHPENDING, &tty->flags))
                                 break;
-                        if (!tty->receive_room || seen_tail)
-                                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(&tty->buf.lock, flags);
-                        disc->ops->receive_buf(tty, char_buf,
+                        copied = disc->ops->receive_buf(tty, char_buf,
                                                         flag_buf, count);
                         spin_lock_irqsave(&tty->buf.lock, flags);
+
+                        head->read += copied;
+
+                        if (copied == 0 || seen_tail) {
+                                schedule_work(&tty->buf.work);
+                                break;
+                        }
                 }
                 clear_bit(TTY_FLUSHING, &tty->flags);
         }