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SubjectRe: [linux-usb] Re: USB device allocation
   Date:   Tue, 5 Oct 1999 18:19:30 -0400
From: Johannes Erdfelt <jerdfelt@sventech.com>

As it stands right now, there is no solution for naming of Plug and Play
devices. I'm specifically interested in USB since that's what I work on,
but this applies to everything plug and play (even PCMCIA)

The problem is if you have 2 mice, how do you name? What if they are
plugged in a different order, now 1 becomes 2 and 2 becomes 1.

How do you differentiate between the 2? This can be difficult in USB
since in some cases, 2 different mice look identical to the software.
The only way you can differentiate is based on topology, exactly where
it's plugged into the bus (which port on which hub).

This is a problem that hasn't been solved yet.

Exactly, and this is why trying to solve the problem in the kernel is
the wrong way to go. There's enough state that you need to store, and
policy that may be different on a per-site basis (user and group
ownership and permissions), the USB topology information, just to name a
few, that trying to do this in the kernel using a dynamic filesystem is
madness.

In userspace, a daemon can store in a database information about where
the mouse is plugged into the USB topology, so that if the user
designates that mouse #1 is the one plugged into the hub built into
their monitor (for example), then on subsequent bootups the daemon can
get this information from the database, and distinguish that mouse from
the mouse that's plugged in somewhere else into the system.

What other problems will be made easy to solve because of the power and
flexibility of doing things in user space? The point is that we don't
know, so we should use the more flexibility solution to solve our
problem, instead of constraining ourselves with devfs.

The big problem people haven't run into yet and haven't solved is the
device naming issue.

Naming is hard, no doubt about it. It's Computer Science's original
rathole. This is why user-visible names (and names in /dev are user
visible) should be done in userspace. We have much more flexibility,
and it makes it much easier to Do The Right Thing.

- Ted

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