Re: [patch 4/6] ps3: Disk Storage Driver

[David Miller <davem@davemloft.net>]

From: Christoph Hellwig <hch@lst.de>
Date: Tue, 19 Jun 2007 07:56:29 +0200

> A SCSI pass through is of course perfectly fine.  If you have a separate
> block passthrough that has additional magic a separate block driver is
> the way to go because it actually is simpler than a scsi driver decoding
> command blocks and translating them to deep magic.  The ps3 storage
> drivers this thread discussed are a good example for that.  We now
> have a very nice and simple disk, scsi and flash chardev driver each
> that don't include abstractions layers and cruft.  Combine that with
> their initial scsi layer driver that was full of internal dispatches
> because each of these device types speaks a completely different command
> set.

That's how I'm currently writing my virtual disk client driver
for the Sun LDOMS stuff, as a block device.

The remaining issues are the partitioning (which we're discussing in
another thread) and how to export the scsi passthru support in such a
non-scsi block driver.

The main disk I/O block read and write is done using descriptors
sent to the disk server.  SCSI pass-through is provided (optionally)
so that disk analysis tools can do things like MODE_SENSE on the
disk.
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