From: Douglas Gilbert <dougg@torque.net>
To: Pat LaVarre <p.lavarre@ieee.org>
Cc: linux-scsi@vger.kernel.org
Subject: Re: zero block writes
Date: Wed, 15 Oct 2003 08:34:24 +1000 [thread overview]
Message-ID: <3F8C79F0.6070105@torque.net> (raw)
In-Reply-To: <1066160907.3501.9.camel@patehci2>
Pat LaVarre wrote:
> $
> $ 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?
Pat,
I find some bugs "interesting". BTW if "if=/dev/zero"
is used the result is more sane :-)
Also when I tested this on scsi_debug, it complained
about getting a NULL data buffer pointer.
> 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.
A new beta (1.05) should be out tomorrow that fixes this
(I just put one up about 1 hour ago).
Doug Gilbert
next prev parent reply other threads:[~2003-10-14 22:35 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-10-14 19:48 zero block writes Pat LaVarre
2003-10-14 22:34 ` Douglas Gilbert [this message]
2003-10-14 23:18 ` Pat LaVarre
2003-10-20 17:55 ` Pat LaVarre
2003-10-20 22:46 ` Pat LaVarre
2003-10-14 22:43 ` Pat LaVarre
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