Re: Re: [PATCH] USB changes for 2.5.58

David Brownell
2003-01-20T21:24:08Z

Oliver Neukum wrote:

> That model cannot be applied to SCSI as it is much more diverse
> in the number of bus types it supports.
> USB can do it, because it knows about hubs. SCSI cannot,
> as there are no hubs in SCSI.

Hubs are irrelevant here, the key functionality is noticing
hardware addition/disconnect. Parts of it can be done in bus
adapter code, parts of it can't. SCSI probes LUNS in much
the same way khubd probes hub ports, and as I recall most of
that logic isn't any more specific to the adapter than virtual
root hub code is for USB.

>>Those disconnect() callbacks have a few key responsibilities, very
>>much including shutting down the entire higher level I/O queue to
>>that device. I think you're saying that SCSI drivers don't have
>>such a responsibility (unlike USB or PCI) ... if so, that would
>>seem to be worth changing.
>
>
> If the scsi layer cannot on its own detect that a device or a bus is gone,
> there'll be no sense in having a callback. It's just a complication.

Erm ... which of the three SCSI layers are you talking about? I was
talking about the highest level, which is precisely the layer I think
has been identified as already needing to know when to shut down the
I/O queues (sd_mod and friends).

- Dave

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