u3g serial device name query

[Hans Petter Selasky]

On Thursday 30 April 2009, Milan Obuch wrote:
> Hi,
>
> I have HUAWEI 3g usb modem. It works with u3g from current. There is
> however one thing I did not get working yet.
>
> When device attaches, it is added into tree as u3gN, devd event is sent. It
> is easily matched with 'device-name "u3g[0-9]"' clause in devd.conf. I can
> start ppp automatically and it works well, given no other USB serial device
> is present.
>
> If another USB serial device such as uplcom is present, u3g serial ports
> does not have the same name. I found no way to relate serial device name to
> this event and looking in source I see no place where it is created. I
> would like to put a devctl notify call there. This way I could start ppp
> with correct device name even if there is some other USB serial device.
>
> Could someone point me in the right direction?

USB serial devices have their own unit management. There is however a way to 
override the unit number through the "usb2_com_tty_name" callback, which 
requires some code changes to the u3g driver.

All USB modems and serial adapters end up with the same naming 
prefix: /dev/cuaU%d.%d, so the assigned numbers must be serialised.

What we could do is to have a separate naming prefix for 3G modems, and use 
the device_get_unit() for unit number.

See: src/sys/dev/usb/serial and usb_serial.c

--HPS