Re: reincarnation of /dev/ttyUSB0 as /dev/ttyUSB1

Uncle George wrote:
> Robert Hancock wrote:
>> It's because you haven't done anything to handle the error which is
> still persisting. Likely the only thing sane you can do in this case
> is close the fd and try to reopen it later.
>>
> This seems to be true, but not for what you might think.
>
> It appears that if u plug the USB/serial device back into the usb-hub,
> the code creates a /dev/ttyUSB1 ( if you have not yet closed the
> disconnected /dev/ttyUSB0. ) When you do close /dev/ttyUSB0, then the
> device is erased from the /dev directory.
>
> Now /dev/ttyUSB1 is the device. And /dev/ttyUSB0 disappeared. This
> does not seem proper. As now the program has no idea or capability to
> re-open the GPS device.

Sure it does. The days of programs being able to blindly assume static 
device names are gone. Hotplug is upon us and it necessitates a 
different way of thinking, even in userspace.

Apps need to be smart enough to re-enumerate compatible devices and pick 
one. Even if the kernel were to maintain the illusion of a static device 
name in the simple case, the app still needs smarts to handle the 
general case. And I say this as the maintainer of  an app that is going 
thru exactly this evolution. It's painful, but necessary.

--Adam


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