USB problem - how to disable an umass device?

[Oliver Fromme]

Ivan Voras wrote:
 > Oliver Fromme wrote:
 > > Of course, a better way to solve the problem would be to
 > > find out _why_ it is hanging in the first place.  :-)
 > > The first step would be to enter the kernel debugger and
 > > take a stack trace, in order to find out where it is stuck.
 > >  
 > > It might be a good idea to take this issue to the freebsd-
 > > usb mailing list.
 > 
 > Actually, it resolved to be a very large timeout, on the order of
 > 5 minutes per step, before something gives up and the boot process
 > continues.

That sounds like a bug where a loop counter isn't initialized
correctly, so a loop wraps around and has to go through the
whole range of a 32 bit int until it terminates, i.e. 2^32
which is 4 billion interations.  Depending on what the loop
actually contains, that could very well take 5 minutes.

There have been bugs like that in the past.

If you enter the Debugger during the hang and print a stack
trace, you should be able to see where that loop is.  Maybe
it's easy to spot the incorrect loop counter and fix it.

 > > > I tried using loader hint hint.usb.2.disabled="1" but it doesn't
 > > > work.
 > >  
 > > Unfortunately, hints cannot be used to disable devices in
 > > general (which would be a desirable feature).  That only
 > > works for legacy devices (i.e. ISA) and some others.
 > 
 > I'd argue that this is actually a bad thing - I'm sure there are
 > situations where it would be useful to disable (almost) arbitrary
 > nodes in the device tree, even down to specific pci busses.

Yes, that's what I mean.  I'm sure it could be useful.

Best regards
   Oliver

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