tty: n_tty: fix SIGIO for output

According to fcntl(2), "a SIGIO signal is sent whenever input
or output becomes possible on that file descriptor", i.e.
after the output buffer was full and now has space for new data.
But in fact SIGIO is sent after every write.

n_tty_write() should set TTY_DO_WRITE_WAKEUP only when
not all data could be written to the buffer.

[pjh: Also fixes missed SIGIO if amt written just happens to be
[     amount still to write

Signed-off-by: Johannes Stezenbach <js@sig21.net>
[pjh: minor patch edits and re-submit]

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index 5ae661cd236eb75f78bd71fc689440ae379e30d4..fad365aa1f5c8622e09887daf74a55234fb3e097 100644 (file)
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -2361,7 +2361,7 @@ static ssize_t n_tty_write(struct tty_struct *tty, struct file *file,
        }
 break_out:
        remove_wait_queue(&tty->write_wait, &wait);
-       if (b - buf != nr && tty->fasync)
+       if (nr && tty->fasync)
                set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
        up_read(&tty->termios_rwsem);
        return (b - buf) ? b - buf : retval;