[resend] oops, sorry, forgot to send the patch!

Hi,

This proposed patch implements enough power-management support within
the SCSI midlayer to get ACPI S3 working on my system. Changes as follows:

* Add generic_scsi_{suspend,resume} methods to scsi.c
* Add suspend and resume callbacks to the scsi_driver structure, and
implement those callbacks in sd.c
* In sd.c, we call sd_shutdown on suspend, in order to synchronize the
write-back cache.
* In sd.c, we call sd_rescan from sd_resume in order to ensure that
drives have spun up and avoid passing not ready errors back to the block
layer.
* In generic_scsi_suspend, we call scsi_device_quiesce before calling
the scsi_driver suspend callback. We resume from quiesce state in
reverse order in generic_scsi_resume.

ACPI S1 and S4/swsusp are untested, but I think there should be no
regressions with S1. To do S1 properly, we probably need to tell the
drive to spin down, and I don't know what the SCSI command is for
that... For S4, the call to scsi_device_quiesce might pose a problem for
the subsequent state dump to disk. But I'm not sure swsusp ever worked
for SCSI.

This might help SATA drives, too, but I seem to remember that the SATA
layer doesn't properly emulate the SYNCHRONIZE_CACHE command.

Comments, anybody? Can this be applied upstream? I think it's a step in
the right direction.

Applies to scsi-misc-2.6

Nathan