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

[Felipe Balbi <balbi-l0cyMroinI0@public.gmane.org>]

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On Mon, Oct 27, 2014 at 05:43:06PM +0200, Kyösti Mälkki wrote:
> 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-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
> >>---
> >>  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.

true, but woudln't the same thing happen with a real UART port using
8250.ko ?

-- 
balbi

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