Re: [PATCH v2 2/2] usb: gadget serial: Honour termios CLOCAL on disconnect

[Peter Hurley <peter-WaGBZJeGNqdsbIuE7sb01tBPR1lH4CV8@public.gmane.org>]

Hi Kyösti,

On 11/03/2014 10:18 AM, Kyösti Mälkki wrote:
> There are applications where it is desirable to not hangup ttyGS* when
> USB disconnect is detected. USB host side of communication may
> power-cycle periodically or there may be the actual need to physically
> disconnect and reconnect USB cable temporarily.
> 
> USB disconnects on serial gadget are comparable to loss of Carrier Detect
> of conventional UARTs. With the change, if ttyGS* has termios CLOCAL flag
> set, disconnect on USB does not hangup the TTY.
> 
> Signed-off-by: Kyösti Mälkki <kyosti.malkki-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
> ---
>  drivers/usb/gadget/function/u_serial.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/usb/gadget/function/u_serial.c b/drivers/usb/gadget/function/u_serial.c
> index 491082a..dabc165 100644
> --- a/drivers/usb/gadget/function/u_serial.c
> +++ b/drivers/usb/gadget/function/u_serial.c
> @@ -1253,9 +1253,16 @@ void gserial_disconnect(struct gserial *gser)
>  	port->port_usb = NULL;
>  	gser->ioport = NULL;
>  	if (port->port.count > 0 || port->openclose) {
> +		struct tty_struct *tty;
> +
>  		wake_up_interruptible(&port->drain_wait);
> -		if (port->port.tty)
> -			tty_hangup(port->port.tty);
> +		tty = port->port.tty;
> +		if (tty) {
> +			if (tty->termios.c_cflag & CLOCAL)
> +				stop_tty(tty);
> +			else
> +				tty_hangup(tty);

It seems you missed my earlier email: what happens if you leave
out the stop_tty() call here?

I ask because the tty is still restartable from userspace after you
stop_tty() here. So if your goal is to prevent write() from
happening, this won't work.

Regards,
Peter Hurley

> +		}
>  	}
>  	spin_unlock_irqrestore(&port->port_lock, flags);
>  
> 

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