zero block writes

[Pat LaVarre <p.lavarre@ieee.org>]

$
$ sg_dd of=/dev/sg0 if=/dev/null bs=2k count=1
0+0 records in
0+0 records out
$

cdb trace tells me this sg utils idiom assaults the device with a zero
block write, specifically:

...
usb-storage: Command WRITE_10 (10 bytes)
usb-storage:  2a 00 00 00 00 00 00 00 00 00
usb-storage: Bulk command S 0x43425355 T 0x1e Trg 0 LUN 0 L 0 F 0 CL 10
...

I wonder if any of you find this sg utils factoid ineffably interesting,
as I do?

I know I have a personal history of pain with the scsi folk who dispute
the t10 claim that the cdb x 0A 00:00:00 00 00 means write out x100
blocks rather than zero and/or while yet that the cdb x 2A 00
00:00:00:00 00 00:00 00 does mean write out zero blocks.

I know I explicitly wrote code into a revision, at a time beyond the
original release of pldd, to discard writes of zero bytes quietly,
rather than passing them thru to the device.

I know such pass thru's trip over such unit attentions as x 6 29 reset.

Pat LaVarre