Re: (remove) event not supported.

[David Brownell <david-b@pacbell.net>]

> Mar 30 08:07:01 localhost /etc/hotplug/usb.agent: USB remove event not supported
> 
> What are the issues associated with it. Is this something that just
> hasn't been coded up or is it something that can't be coded up.

Awkward to code up.  What one really wants to happen is have
the device's module removed ... and _maybe_ some driver-specific
action (not that I can think of any examples just now).  But:

- the dynamic linking framework doesn't track how many devices
  are attached to each driver module ... so if there's another device
  controlled by the same driver, but it's not opened, removing that
  module would be incorrect.  ("module use count" doesn't cover
  uses, just opens.)

- nothing's tracking which modules are used with which device,
  and if the device is gone you can't query it to find that out!

Such issues aren't specific to USB; any hotpluggable bus has such
problems.  But it's worst for USB:  PCMCIA and Cardbus
tend to only have one device of a type at a time, and typically
only have two slots, but USB can handle a hundred devices,
and it's not that uncommon to have multiple devices.


> If it simply hasn't been written, if you give me a few pointers on how
> it should be written. I'll code it up.

I think that it'll be tough to provide a "good" fix for this without
updating the module framework; and that maybe a few other
issues will show up too.  But maybe there are better ways to
look at this problem.

- Dave




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