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

["Kyösti Mälkki" <kyosti.malkki@gmail.com>]

On 10/27/2014 03:38 PM, Felipe Balbi wrote:
> Hi,
>
> On Sun, Oct 26, 2014 at 08:01:30PM +0200, 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@gmail.com>
>> ---
>>   drivers/usb/gadget/function/u_serial.c | 9 +++++++--
>>   1 file changed, 7 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/usb/gadget/function/u_serial.c b/drivers/usb/gadget/function/u_serial.c
>> index 491082a..e68ffd7 100644
>> --- a/drivers/usb/gadget/function/u_serial.c
>> +++ b/drivers/usb/gadget/function/u_serial.c
>> @@ -1254,8 +1254,13 @@ void gserial_disconnect(struct gserial *gser)
>>   	gser->ioport = NULL;
>>   	if (port->port.count > 0 || port->openclose) {
>>   		wake_up_interruptible(&port->drain_wait);
>> -		if (port->port.tty)
>> -			tty_hangup(port->port.tty);
>> +		struct tty_struct *tty = port->port.tty;
>
> declare above as Sergei said.
>
>> +		if (tty) {
>
> is there any situation where tty would be NULL here ?
>
>> +			if (tty->termios.c_cflag & CLOCAL)
>> +				stop_tty(tty);
>> +			else
>> +				tty_hangup(tty);
>
> this I'll defer to Greg who also maintains tty.
>

My main concern is if someone runs getty on ttyACM without explicitly 
clearing CLOCAL. With the patch here login session would no longer get 
SIGHUP if cable is disconnected. And it is not possible to tell if it is 
the same cable that is plugged back in.

KM




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