Re: [PATCH] scsi_set_host_offline (resend)

[Oliver Neukum <oliver@neukum.org>]

> *But*, the _important__point_ is that the LLDD must be able to handle
> requests (queuecommand()) to non-existant (== just removed) devices,
> and not oops, or whatever.

For how long? That's the question.

> So, in effect, you just call usb_dev_removal(dev) (to be written),
> and free _your_ resources on the device. (note important point above)

The way it is in USB is a little different as the USB device drivers do
not go directly to the hardware. It would be:

HCD -> USB core -> LLDD -> generic SCSI -> ...
Steps 1 to 3 work, 4 doesn't.
For a PCMCIA LLDD it would be different, but that really doesn't
matter to the generic SCSI layer.

> > We have indeed discussed this before and the need to notify
> > user space was never questioned, as far as I recall.
> > The point of contention always was whether the notification
> > had to do specific things for the process of unplugging to finish
> > as far as it concerns the low level driver.
>
> Right.  As far as I can see, those subsystem entries, xxx_dev_removal(dev),
> would do things which do not block, like flip a bit, flags, integer,
> wake up a thread, etc, call the above subsystem's xxx_dev_removal(dev),
> and return immediately. (as per my other posting)
> (this needs more thinking though)

If they can't block, they cannot clean up commands still in flight.
Eventually something needs to wait for the outstanding commands.

	Regards
		Oliver