On Mon, Apr 10, 2000, Dunlap, Randy <[EMAIL PROTECTED]> wrote:
>
> Would it make any sense to resurrect my old suggestion/idea
> of using round-robin USB device numbers instead of
> always assigning the lowest number available or is it
> considered bad? It could cause some user confusion also.
>
> Actually I think I like the _concept_ that you are suggesting,
> Johannes. Sounds like a way to keep using low-numbered device
> IDs unless they shouldn't be reused. I'm not so hot
> on depending on an application to do this, though.
> I'd prefer to see another solution that has the same effect,
> but I'm struggling with how to do that.
>
> I'm just thinking aloud (so to speak)...maybe have dual
> modes of device number assignment, default is LOWEST_AVAIL.
> On disconnects, set mode to ROUND_ROBIN.
> This applies to the next connect. After this next
> connect, set mode back to LOWEST_AVAIL.
> Sounds like a kludge, right? And all that it does
> is reduce the window size for the race condition,
> not eliminate it. Using round robin all the time
> is the extreme case of minimizing the window size,
> especially since it's not real likely that someone
> will actually have 127 devices.
The ROUND_ROBIN idea would make the problem more difficult to trigger,
but it doesn't completely solve the problem. There still is a (very
difficult to trigger) race there.
The ultimate problem is the applicate needs to inform the USB kernel
code it's still using the device, so it won't try reassigning that USB
id to a new device.
The easiest way to do this, and track abnormal termination of a program,
is to open a file and keep it open. I think it's a reasonable solution,
which is both safe and easy, as long as we mandate to user space
programs that they do this, or they'll have the possibility of races.
JE
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