Re: USB filter driver

--- David Brownell <[email protected]> wrote:

> ISTR a couple versions of that; one was more generally
> USB-over-IP, posted to this list in the last year or
> two by someone from Japan.

OK, thanks I will try to find it.

> You didn't answer the first question:  how it could help
> write HCDs.  (Capitalization of FUSE was not confusing.)

Suppose you have an arbitrary USB host controller chip 
with an i2c interface connected to your parallel port.
Let's say you want to connect a bluetooth dongle to such
a device and communicate with your PDA using SPP.

Theoretically you can communicate with the PDA using nothing
more than i2cget and i2cset, but you'd have to implement 
(or hack) Bluez and a bunch of other stuff around it to 
achieve this.  It would be nice to use the code in the 
kernel (not to mention all the software which is compatible
with it) instead.  Once your 'driver' is implemented as a 
normal process you can decide whether to migrate it to 
a real kernel driver, or if performance is acceptable leave
it as-is.

So first you deal with the problem of understanding your
controller, next you deal with the integration issues.
Debugging applications is almost always more 
straightforward than debugging the kernel.

> > > two components; but HCDs ("controller drivers") talk right
> > > to the hardware.
> > 
> > > > Is such a thing even feasible
> > > 
> > > You'd have to explain what you meant before that could
> > > be answered.  But given the partial explanation you've
> > > already given, I suspect not.
> > 
> > I thought that such a filter might be able to intercept the
> > URB operations in some useful way, but by the sound of it
> > the answer is no.
> 
> You would still need to explain what you mean.
> And not by reference to MS-Windows, since most
> people here don't know that environment (and
> don't want to).
> 
> For example, does "some useful way" imply being a
> huge security hole, being able to insert and remove
> messages?  

Yes.  I don't care about security in this case
because my primary interest is in embedded applications
where local user access isn't such an issue.
I also don't care if I bring down the system while I'm
developing the thing.  My interest is only in
implementing functionality in the highest-level 
language possible (maybe even Perl) to get the job 
done.

-biff.


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