* zero block writes
@ 2003-10-14 19:48 Pat LaVarre
2003-10-14 22:34 ` Douglas Gilbert
2003-10-14 22:43 ` Pat LaVarre
0 siblings, 2 replies; 6+ messages in thread
From: Pat LaVarre @ 2003-10-14 19:48 UTC (permalink / raw)
To: linux-scsi
$
$ 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
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: zero block writes
2003-10-14 19:48 zero block writes Pat LaVarre
@ 2003-10-14 22:34 ` Douglas Gilbert
2003-10-14 23:18 ` Pat LaVarre
2003-10-20 22:46 ` Pat LaVarre
2003-10-14 22:43 ` Pat LaVarre
1 sibling, 2 replies; 6+ messages in thread
From: Douglas Gilbert @ 2003-10-14 22:34 UTC (permalink / raw)
To: Pat LaVarre; +Cc: linux-scsi
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
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: zero block writes
2003-10-14 22:34 ` Douglas Gilbert
@ 2003-10-14 23:18 ` Pat LaVarre
2003-10-20 17:55 ` Pat LaVarre
2003-10-20 22:46 ` Pat LaVarre
1 sibling, 1 reply; 6+ messages in thread
From: Pat LaVarre @ 2003-10-14 23:18 UTC (permalink / raw)
To: dougg; +Cc: linux-scsi
> Also when I tested this on scsi_debug, it complained
> about getting a NULL data buffer pointer.
CONFIG_SCSI_DEBUG option of .config was new to me, thanks.
> > $ sg_dd of=/dev/sg0 if=/dev/null bs=2k count=1
> > ...
> > usb-storage: Command WRITE_10 (10 bytes)
> ...
> bugs ...
Is this a bug?
Because CONFIG_SCSI_DEBUG complains of NULL pointers?
What patch do you like? No command at all? A zeroed command with no
NULL pointers?
I vote for the patch of no command at all because for me sg_dd exists to
let me read and write fragments longer than I can conveniently in the
single cdb of a single SG_IO. For me sg_dd doesn't exist to pass thru
creative variations of SG_IO. Ditto for you?
I'm guessing I have a clue what round means near hear because to get
that clue I reinvented the sg_dd wheel myself. In my pldd I included a
-v option to give me a cdb trace without reconfiguring the kernel to run
slow, so there I noticed this issue more quickly.
> A new beta (1.05) ... tomorrow ...
> one up about 1 hour ago).
Highly responsive, thank you.
I do enjoy perusing the links to the sg home page i.e.
http://www.google.com/search?q=link:www.torque.net/sg/
A google mystery of this moment is why google doesn't yet know that the
page where I discuss my reinvented sg_dd indeed does link to sg utils,
I can prove Google has my page cached. The search:
http://www.google.com/search?q=LaVarre+pldd
finds:
http://members.aol.com/plscsi/tools/pldd/
Yet seemingly Google hasn't yet parsed all the links from pldd.
Pat LaVarre
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: zero block writes
2003-10-14 22:34 ` Douglas Gilbert
2003-10-14 23:18 ` Pat LaVarre
@ 2003-10-20 22:46 ` Pat LaVarre
1 sibling, 0 replies; 6+ messages in thread
From: Pat LaVarre @ 2003-10-20 22:46 UTC (permalink / raw)
To: dougg; +Cc: linux-scsi
> > $ 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
> > ...
>
> A new beta (1.05) should be out tomorrow that fixes this
> (I just put one up about 1 hour ago).
Looks good, thank you. Again I tried contrasting:
sg_dd of=/dev/sg0 if=/dev/zero bs=2k count=1
sg_dd of=/dev/sg0 if=/dev/null bs=2k count=1
I'm pleased to report the sg3_utils-1.05.tar.gz I fetched today passes
cdb's thru drivers/usb/storage/usb.usb_stor_show_command only from
/dev/zero, not from /dev/null.
Pat LaVarre
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: zero block writes
2003-10-14 19:48 zero block writes Pat LaVarre
2003-10-14 22:34 ` Douglas Gilbert
@ 2003-10-14 22:43 ` Pat LaVarre
1 sibling, 0 replies; 6+ messages in thread
From: Pat LaVarre @ 2003-10-14 22:43 UTC (permalink / raw)
To: linux-scsi
> $
> $ sg_dd of=/dev/sg0 if=/dev/null bs=2k count=1
> 0+0 records in
> 0+0 records out
> $
> ...
> usb-storage: 2a 00 00 00 00 00 00 00 00 00
Kindly offline I'm told I neglected to emphasise, that example of an sg
utils sg_dd if=/dev/null command line differs only subtly from the
perhaps more familiar:
sg_dd of=/dev/sg0 if=/dev/zero bs=2k count=1
Copying from /dev/zero by design writes lots of zeroed bytes.
Copying from /dev/null via sg_dd doesn't neglect to write, in fact it
does write, it just tries to write nothing at a specific address.
Consider, for example:
sg_dd of=/dev/sg0 if=/dev/zero bs=2k seek=259 count=1
That changes the cdb trace so that the starting address passed thru as
cdb bytes[2:3:4:5] become x 00:00:01:03 rather than x 00:00:00:00:
x 2A 00 00 00 01 03 00 00 01 00
Pat LaVarre
P.S. Yes indeed I did stumble into this to-me-surprising fact via the
bonehead newbie error of typing "null" where I meant "zero".
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2003-10-20 22:46 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2003-10-14 19:48 zero block writes Pat LaVarre
2003-10-14 22:34 ` Douglas Gilbert
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
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.