Re: [linux-usb-devel] Re: usb storage cleanup

[David Brownell]

Matthew Dharm wrote:
> Now... wait a second here....
> 
> You say the dirver "is supposed to wait until all urbs" are completed...
> but we're talking about the case where the device is now gone...
> 
> So how do the urbs complete?  Something is causing them to complete when
> the cable is removed -- that's the behavior I've observed, at least.

Normally I'd expect the device driver to forcibly unlink
anything it's started.  Failing that, the host controller
will often fail the transfer if the device is gone.  (But
I seem to recall recent speculation about maybe one of the
UHCIs not doing that.)

In either case, the device driver should block until all
its pending URBs complete.

- Dave

> Matt
> 
> On Thu, Jul 04, 2002 at 01:23:54PM -0700, David Brownell wrote:
> 
>>>>Test case: user pulls out the usb cable while a transfer is in progress. 
>>>>urb submitted to the device, reply not yet received.
>>>>Result: storage_disconnect() would hang for 20 seconds until 
>>>>command_abort() is called.
>>>
>>>
>>>No, not quite.   The HCD accelerates the URBs to completion if the device
>>>is removed with an URB pending on it.  It therefore shouldn't hang for the
>>>timeout -- if you're seeing this behavior, then the HCD is broken.
>>
>>Actually all of the interesting work is triggered by khubd,
>>and then the device driver.
>>
>>Khubd calls usb_disconnect() for the device.  That disconnects
>>each driver (which is supposed to wait until all urbs it's
>>submitted have completed, and not submit any more URBS).
>>
>>Only at the very end of this does the HCD hear anything about
>>devices going away.  If there's any URB still submitted at that
>>point it's not a bug in the HCD at all ... but in a device
>>driver that didn't implement disconnect() correctly.
>>
>>- Dave
>>
>>
>>
> 
>