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When the host does not read the port, for example because no application on the host has it open, the last close blocks for the full timeout. tcflush(TCOFLUSH) cannot avoid that: u_serial has no flush_buffer operation, so the request is a no-op. Implement flush_buffer: discard the buffered output under the port lock and wake up the close and write waiters. As on other tty drivers, a hangup and an interrupt character (ISIG without NOFLSH) now discard the pending output as well. Signed-off-by: Mehmet Fide --- drivers/usb/gadget/function/u_serial.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/drivers/usb/gadget/function/u_serial.c b/drivers/usb/gadget/function/u_serial.c index cdd1dfc666c4..2b99e33cbf3a 100644 --- a/drivers/usb/gadget/function/u_serial.c +++ b/drivers/usb/gadget/function/u_serial.c @@ -822,6 +822,19 @@ static void gs_flush_chars(struct tty_struct *tty) spin_unlock_irqrestore(&port->port_lock, flags); } +static void gs_flush_buffer(struct tty_struct *tty) +{ + struct gs_port *port = tty->driver_data; + unsigned long flags; + + spin_lock_irqsave(&port->port_lock, flags); + kfifo_reset(&port->port_write_buf); + spin_unlock_irqrestore(&port->port_lock, flags); + + wake_up_interruptible(&port->drain_wait); + tty_wakeup(tty); +} + static unsigned int gs_write_room(struct tty_struct *tty) { struct gs_port *port = tty->driver_data; @@ -914,6 +927,7 @@ static const struct tty_operations gs_tty_ops = { .write = gs_write, .put_char = gs_put_char, .flush_chars = gs_flush_chars, + .flush_buffer = gs_flush_buffer, .write_room = gs_write_room, .chars_in_buffer = gs_chars_in_buffer, .unthrottle = gs_unthrottle, -- 2.55.0