[PATCH] Ghost devices being reported with AIC7XXX version 6.2.6

[PATCH] Ghost devices being reported with AIC7XXX version 6.2.6

[Mike Brown]

Hi,

It seems the kernel reintroduced a bug that I fixed a year ago
regarding phantom devices being reported by the aic7xxx driver.
The problem is that the AIC driver defines the maximum LUs it
supports as 64 (aic7xxx.h:#define AHC_NUM_LUNS 64).  Symmetrix
reports SCSI_2 devices which according to the spec means no
target supports more than 8 LUs (LUN 0-7) per target id.  However,
since the Symmetrix can be configured to support more than 8 LUs per
target id, its tagged in the blacklist with the BLIST_LARGELUN flag,
which trips the scanning code into treating the Symmetrix as a
SCSI_3 device:

drivers/scsi/scsi_scan.c:

	{"EMC", "SYMMETRIX", "*", BLIST_SPARSELUN | BLIST_LARGELUN | BLIST_FORCELUN},

..........

	/* don't probe further for luns > 7 for targets <= SCSI_2 */
	if ((lun0_sl < SCSI_3) && (lun > 7))
		break;

	if (!scan_scsis_single(channel, order_dev, lun, lun0_sl,
			       &max_dev_lun, &sparse_lun, &SDpnt, shpnt,
			       scsi_result) && !sparse_lun)
		break;	/* break means don't probe further for luns!=0 */
	if (SDpnt && (0 == lun)) {
		int bflags = get_device_flags (scsi_result);
		if (bflags & BLIST_LARGELUN)
			lun0_sl = SCSI_3; /* treat as SCSI 3 */
		else
			lun0_sl = SDpnt->scsi_level;


This isn't a problem so far until we start scanning LUN > 31.  The
SCSI_3 IDENTIFY Message Format defines 6 bits for LUN, but since
Symmetrix reports its devices as SCSI_2, we follow the SCSI_2 IDENTIFY
Message Format which defines 3 bits for the LUNTRN, and we also
use the 2 reserved bits which gives us 5 bits or 32 LUs.  So, when
the SCSI subsystem begins scanning for LUNs > 31, the aic7xxx driver
reports devices that are actually (LUN & 0x0000001f) and LUNs that
have already been reported are re-reported, hence the phantom device
problem.

Justin can you change AHC_NUM_LUNS to 32 or suggest an alternative fix?

Alternatively a new BLIST_FLAG could be defined.  This also has its
problems because Fibre attached Symm's work with LUN > 31 without
problems since the IDENTIFY Message is unique to Parallel.  Perhaps another
option is to add a "ahc_num_luns=xxx" module parameter allowing
the decision to be made at runtime.

Please cc: me on linux replies as I'm not currently subscribed.

--------CUT HERE---------
--- linux-2.4.19/drivers/scsi/aic7xxx/aic7xxx.h.orig	Wed Aug  7 09:31:30 2002
+++ linux-2.4.19/drivers/scsi/aic7xxx/aic7xxx.h	Thu Oct 31 12:12:26 2002
@@ -122,7 +122,7 @@
  * You can have 2^64 luns when information unit transfers are enabled,
  * but it is doubtful this driver will ever support IUTs.
  */
-#define AHC_NUM_LUNS 64
+#define AHC_NUM_LUNS 32
 
 /*
  * The maximum transfer per S/G segment.
--------CUT HERE---------

-Michael F. Brown, EMC Corp.

Email:            mbrown@emc.com
EMC Tie Line:             x43416
External Line:    (508) 249-3416

"5 years from now everyone will be running free
 GNU on their 200 MIPS, 64M SPARCstation-5."      -Andrew Tanenbaum '92

(In late 1997 I installed Linux for the first time on my 200Mhz, 128M
 AMD x86 clone)

Re: [PATCH] Ghost devices being reported with AIC7XXX version 6.2.6

[Justin T. Gibbs]

> Justin can you change AHC_NUM_LUNS to 32 or suggest an alternative fix?

The aic7xxx driver is not at fault and so should not be changed.
The aic7xxx driver really does support all 64 luns.  In my opinion,
there are three problems here:

1) The Symetrix should treat a non-zero LUNTAR bit as an invalid
   selection.  This would prevent these higher luns from showing up
   as valid devices.

2) Linux should never use more than 5 bits of lun for a device that
   reports itself as SCSI-2.  If the lun is larger than what will
   fit in 3 bits, byte 1 of the CDB should not be altered even if
   the device is SCSI2.

3) Linux should be using the Report Luns command to determine how
   many luns are on a device and at what locations.  This might
   even allow you to never probe more than 8 luns on a SCSI 2
   device unless they support this command.  Does the Symetrix support
   it?  Going beyond 8 luns on a SCSI2 device is really a hack
   otherwise.

--
Justin

Re: [PATCH] Ghost devices being reported with AIC7XXX version 6.2.6

[Matthew Jacob]

> > Justin can you change AHC_NUM_LUNS to 32 or suggest an alternative fix?
> 
> The aic7xxx driver is not at fault and so should not be changed.
> The aic7xxx driver really does support all 64 luns.  In my opinion,
> there are three problems here:
> 
> 1) The Symetrix should treat a non-zero LUNTAR bit as an invalid
>    selection.  This would prevent these higher luns from showing up
>    as valid devices.
> 
> 2) Linux should never use more than 5 bits of lun for a device that
>    reports itself as SCSI-2.  If the lun is larger than what will
>    fit in 3 bits, byte 1 of the CDB should not be altered even if
>    the device is SCSI2.
> 
> 3) Linux should be using the Report Luns command to determine how
>    many luns are on a device and at what locations.  This might
>    even allow you to never probe more than 8 luns on a SCSI 2
>    device unless they support this command.  Does the Symetrix support
>    it?  Going beyond 8 luns on a SCSI2 device is really a hack
>    otherwise.

Absolutely.

Re: [PATCH] Ghost devices being reported with AIC7XXX version 6.2.6

[Alan Cox]

On Thu, 2002-10-31 at 18:28, Matthew Jacob wrote:
> > 3) Linux should be using the Report Luns command to determine how
> >    many luns are on a device and at what locations.  This might
> >    even allow you to never probe more than 8 luns on a SCSI 2
> >    device unless they support this command.  Does the Symetrix support
> >    it?  Going beyond 8 luns on a SCSI2 device is really a hack
> >    otherwise.
> 
> Absolutely.

Now is the right time to fix this properly for 2.5

Re: [PATCH] Ghost devices being reported with AIC7XXX version 6.2.6

[Matthew Jacob]

> On Thu, 2002-10-31 at 18:28, Matthew Jacob wrote:
> > > 3) Linux should be using the Report Luns command to determine how
> > >    many luns are on a device and at what locations.  This might
> > >    even allow you to never probe more than 8 luns on a SCSI 2
> > >    device unless they support this command.  Does the Symetrix support
> > >    it?  Going beyond 8 luns on a SCSI2 device is really a hack
> > >    otherwise.
> > 
> > Absolutely.
> 
> Now is the right time to fix this properly for 2.5
> 
> 

Well, yes.

Re: [PATCH] Ghost devices being reported with AIC7XXX version 6.2.6

[Doug Ledford]

On Thu, Oct 31, 2002 at 11:30:57AM -0800, Matthew Jacob wrote:
> 
> 
> > On Thu, 2002-10-31 at 18:28, Matthew Jacob wrote:
> > > > 3) Linux should be using the Report Luns command to determine how
> > > >    many luns are on a device and at what locations.  This might
> > > >    even allow you to never probe more than 8 luns on a SCSI 2
> > > >    device unless they support this command.  Does the Symetrix support
> > > >    it?  Going beyond 8 luns on a SCSI2 device is really a hack
> > > >    otherwise.
> > > 
> > > Absolutely.
> > 
> > Now is the right time to fix this properly for 2.5
> > 
> > 
> 
> Well, yes.

2.5 does this already.

-- 
  Doug Ledford <dledford@redhat.com>     919-754-3700 x44233
         Red Hat, Inc. 
         1801 Varsity Dr.
         Raleigh, NC 27606
  

Re: [PATCH] Ghost devices being reported with AIC7XXX version 6.2.6

[Matthew Jacob]

> On Thu, Oct 31, 2002 at 11:30:57AM -0800, Matthew Jacob wrote:
> > 
> > 
> > > On Thu, 2002-10-31 at 18:28, Matthew Jacob wrote:
> > > > > 3) Linux should be using the Report Luns command to determine how
> > > > >    many luns are on a device and at what locations.  This might
> > > > >    even allow you to never probe more than 8 luns on a SCSI 2
> > > > >    device unless they support this command.  Does the Symetrix support
> > > > >    it?  Going beyond 8 luns on a SCSI2 device is really a hack
> > > > >    otherwise.
> > > > 
> > > > Absolutely.
> > > 
> > > Now is the right time to fix this properly for 2.5
> > > 
> > > 
> > 
> > Well, yes.
> 
> 2.5 does this already.


*blush*

I was actually going to start finally working 2.5 next week (don't hit
me! don't hit me)

Re: [PATCH] Ghost devices being reported with AIC7XXX version 6.2.6

[Doug Ledford]

On Thu, Oct 31, 2002 at 11:03:19AM -0700, Justin T. Gibbs wrote:
> > Justin can you change AHC_NUM_LUNS to 32 or suggest an alternative fix?
> 
> The aic7xxx driver is not at fault and so should not be changed.
> The aic7xxx driver really does support all 64 luns.  In my opinion,
> there are three problems here:
> 
> 1) The Symetrix should treat a non-zero LUNTAR bit as an invalid
>    selection.  This would prevent these higher luns from showing up
>    as valid devices.
> 
> 2) Linux should never use more than 5 bits of lun for a device that
>    reports itself as SCSI-2.  If the lun is larger than what will
>    fit in 3 bits, byte 1 of the CDB should not be altered even if
>    the device is SCSI2.

The whole "support more than 8 luns on SCSI-2 devices" is a hack anyway, I 
would be more likely to just remove it instead of changing other things.

> 3) Linux should be using the Report Luns command to determine how
>    many luns are on a device and at what locations.  This might
>    even allow you to never probe more than 8 luns on a SCSI 2
>    device unless they support this command.  Does the Symetrix support
>    it?  Going beyond 8 luns on a SCSI2 device is really a hack
>    otherwise.

We currently only do report luns on SCSI-3 devices.  I didn't think this 
was a supported command on SCSI-2, but I hadn't checked the spec 
recently...hmmm...nope, not supported in SCSI-2, so using report luns on 
SCSI-2 devices is just as much a hack as going above lun 7 on SCSI-2 
devices without specific knowledge of transfer interconnect.

> --
> Justin
> -
> To unsubscribe from this list: send the line "unsubscribe linux-scsi" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

-- 
  Doug Ledford <dledford@redhat.com>     919-754-3700 x44233
         Red Hat, Inc. 
         1801 Varsity Dr.
         Raleigh, NC 27606
  

Re: [PATCH] Ghost devices being reported with AIC7XXX version 6.2.6

[Doug Ledford]

On Thu, Oct 31, 2002 at 12:04:16PM -0800, Matthew Jacob wrote:
> 
> *blush*
> 
> I was actually going to start finally working 2.5 next week (don't hit
> me! don't hit me)

Hehehe!  Going to start after the feature freeze is already over, makes it 
kind of hard to get anything new in doesn't it ;-)

-- 
  Doug Ledford <dledford@redhat.com>     919-754-3700 x44233
         Red Hat, Inc. 
         1801 Varsity Dr.
         Raleigh, NC 27606
  

Re: [PATCH] Ghost devices being reported with AIC7XXX version 6.2.6

[Matthew Jacob]

> 
> We currently only do report luns on SCSI-3 devices.  I didn't think this 
> was a supported command on SCSI-2, but I hadn't checked the spec 
> recently...hmmm...nope, not supported in SCSI-2, so using report luns on 
> SCSI-2 devices is just as much a hack as going above lun 7 on SCSI-2 
> devices without specific knowledge of transfer interconnect.

It's transitional in that a number of devices report as SCSI-2 but do
things like REPORT LUNs. It's changing very fast though.

Re: [PATCH] Ghost devices being reported with AIC7XXX version 6.2.6

[Matthew Jacob]

> On Thu, Oct 31, 2002 at 12:04:16PM -0800, Matthew Jacob wrote:
> > 
> > *blush*
> > 
> > I was actually going to start finally working 2.5 next week (don't hit
> > me! don't hit me)
> 
> Hehehe!  Going to start after the feature freeze is already over, makes it 
> kind of hard to get anything new in doesn't it ;-)

Well, look- doing feature freezes early is all well and swell, but
remember that a lot of us out here, if we get any work stuff at all for
Linux, has us concentrate on 2.4, or even 2.2.

The only people to ever mention 2.5 recently did so because they're
planning for next year.

Early feature freezes are great for those who are *on* the long term
train and are comfortable with shoving things out a year. This, btw, is
one of things I detested about Sun when I worked there. Drivers and
driver subsystems are candidates for late binding and late changing
because they are typically isolated areas.

It's also true that I haven't really been involved other than kibitzing
for 2.5. It would have required me to be a lot more tightly involved in
the Linux world than I have been. My best hope is to comment with
perspective outside of Linux and debug and offer alternatives where
possible- that way I can remain positive and perhaps helpful when I
cannot put in all the time that I either can or would like to do.

Hmph. If we'd actually connected and I'd gone to work for RH 18mos ago,
this all would be a moot discussion.

-matt

Re: [PATCH] Ghost devices being reported with AIC7XXX version 6.2.6

[Doug Ledford]

On Thu, Oct 31, 2002 at 12:26:15PM -0800, Matthew Jacob wrote:
> > 
> > We currently only do report luns on SCSI-3 devices.  I didn't think this 
> > was a supported command on SCSI-2, but I hadn't checked the spec 
> > recently...hmmm...nope, not supported in SCSI-2, so using report luns on 
> > SCSI-2 devices is just as much a hack as going above lun 7 on SCSI-2 
> > devices without specific knowledge of transfer interconnect.
> 
> It's transitional in that a number of devices report as SCSI-2 but do
> things like REPORT LUNs. It's changing very fast though.

And we recently added INQUIRY with the EVPD bit set and an EVPD page 0.  
>From the reports I've seen, I'm pretty sure it's causing a more than
trivial number of devices to lock up on boot.  I suspect blindly pulling a
REPORT_LUNS on SCSI-2 devices would likely cause similar problems.

-- 
  Doug Ledford <dledford@redhat.com>     919-754-3700 x44233
         Red Hat, Inc. 
         1801 Varsity Dr.
         Raleigh, NC 27606
  

Re: [PATCH] Ghost devices being reported with AIC7XXX version 6.2.6

[Mike Brown]

Hi,

> The whole "support more than 8 luns on SCSI-2 devices" is a hack anyway, I 
> would be more likely to just remove it instead of changing other things.

This would break production environments.  Symmetrix isn't the only
storage array that supports this hack.  DG, Dell, HP, and others also
support this hack.  If its taken out in 2.5 and replaced with
REPORT_LUNS that'd be ok, but taking it out of 2.4 without replacing
it with REPORT_LUNS is going to break people.

> > 3) Linux should be using the Report Luns command to determine how
> >    many luns are on a device and at what locations.  This might
> >    even allow you to never probe more than 8 luns on a SCSI 2
> >    device unless they support this command.  Does the Symetrix support
> >    it?  Going beyond 8 luns on a SCSI2 device is really a hack
> >    otherwise.
> 
> We currently only do report luns on SCSI-3 devices.  I didn't think this 
> was a supported command on SCSI-2, but I hadn't checked the spec 
> recently...hmmm...nope, not supported in SCSI-2, so using report luns on 
> SCSI-2 devices is just as much a hack as going above lun 7 on SCSI-2 
> devices without specific knowledge of transfer interconnect.

Symmetrix supports Report Luns despite reporting SCSI_2 Units.  The
problem is that because Symmetrix in the device table with
a BLIST_LARGELUN flag, this block gets tripped in the scanning code:

	if (SDpnt && (0 == lun)) {
		int bflags = get_device_flags (scsi_result);
		if (bflags & BLIST_LARGELUN)
			lun0_sl = SCSI_3; /* treat as SCSI 3 */
		else
			lun0_sl = SDpnt->scsi_level;
	}

The quick fix is to change the AIC driver's max lun value to 32, but
Justin's right, its not the AIC driver with the problem.  I don't know
what the right fix is for 2.4.  We need a hack akin to something like:

	if ((bflags & BLIST_LARGELUN) && !shpnt->is_fibre && lun > 31)
		/* IDENTIFY only has 5 bits for LUN including reserved hack */
		break;
	else if ((lun0_sl < SCSI_3) && (lun > 7))
		/* don't probe further for luns > 7 for targets <= SCSI_2 */
		break;

	if (!scan_scsis_single(channel, order_dev, lun, lun0_sl,
		 	       &max_dev_lun, &sparse_lun, &SDpnt, shpnt,
			       scsi_result) && !sparse_lun)
		break;	/* break means don't probe further for luns!=0 */

	if (SDpnt && (0 == lun))
		lun0_sl = SDpnt->scsi_level;

and to get rid of this logic:

	if (SDpnt && (0 == lun)) {
		int bflags = get_device_flags (scsi_result);
		if (bflags & BLIST_LARGELUN)
			lun0_sl = SCSI_3; /* treat as SCSI 3 */
		else
			lun0_sl = SDpnt->scsi_level;

Comments?  Again please cc: me for list replies.

-Michael F. Brown, EMC Corp.

Email:            mbrown@emc.com

"5 years from now everyone will be running free
 GNU on their 200 MIPS, 64M SPARCstation-5."      -Andrew Tanenbaum '92

(In late 1997 I installed Linux for the first time on my 200Mhz, 128M
 AMD x86 clone)

Re: [PATCH] Ghost devices being reported with AIC7XXX version 6.2.6

[Matthew Jacob]

> And we recently added INQUIRY with the EVPD bit set and an EVPD page 0.  
> From the reports I've seen, I'm pretty sure it's causing a more than
> trivial number of devices to lock up on boot.  I suspect blindly pulling a
> REPORT_LUNS on SCSI-2 devices would likely cause similar problems.

That's less likely than the EVPD stuff which seems to make more devices
choke than not.

I would suggest the following for REPORT LUNS usage on SCSI-2 devices:

+ a config option (so it goes away in a year) to enable REPORT LUNS on
SCSI-2, or set an uppper SCSI-2 lun scan limit.

+ REPORT LUNS will only be used on SCSI-2 devices that are DIRECT ACCESS
(sorry, ATL && other tape and tape emulator folks)

Re: [PATCH] Ghost devices being reported with AIC7XXX version 6.2.6

[Matthew Jacob]

> 
> The only people to ever mention 2.5 recently did so because they're
                                     v
				 "to me"
> planning for next year.

Re: [PATCH] Ghost devices being reported with AIC7XXX version 6.2.6

[Mike Brown]

> And we recently added INQUIRY with the EVPD bit set and an EVPD page 0.  
> >From the reports I've seen, I'm pretty sure it's causing a more than
> trivial number of devices to lock up on boot.  I suspect blindly pulling a
> REPORT_LUNS on SCSI-2 devices would likely cause similar problems.

What about adding BLIST_FORCE_REPORT_LUNS?

-Michael F. Brown, EMC Corp.

Email:            mbrown@emc.com
EMC Tie Line:             x43416
External Line:    (508) 249-3416

"5 years from now everyone will be running free
 GNU on their 200 MIPS, 64M SPARCstation-5."      -Andrew Tanenbaum '92

(In late 1997 I installed Linux for the first time on my 200Mhz, 128M
 AMD x86 clone)

Re: [PATCH] Ghost devices being reported with AIC7XXX version 6.2.6

[Matthew Jacob]

Yeah, but lets get out of the tailchasing exercise of list updates if we
can...


> > And we recently added INQUIRY with the EVPD bit set and an EVPD page 0.  
> > >From the reports I've seen, I'm pretty sure it's causing a more than
> > trivial number of devices to lock up on boot.  I suspect blindly pulling a
> > REPORT_LUNS on SCSI-2 devices would likely cause similar problems.
> 
> What about adding BLIST_FORCE_REPORT_LUNS?
> 
> -Michael F. Brown, EMC Corp.
> 
> Email:            mbrown@emc.com
> EMC Tie Line:             x43416
> External Line:    (508) 249-3416
> 
> "5 years from now everyone will be running free
>  GNU on their 200 MIPS, 64M SPARCstation-5."      -Andrew Tanenbaum '92
> 
> (In late 1997 I installed Linux for the first time on my 200Mhz, 128M
>  AMD x86 clone)
> 

Re: [PATCH] Ghost devices being reported with AIC7XXX version 6.2.6

[Doug Ledford]

On Thu, Oct 31, 2002 at 12:27:44PM -0800, Matthew Jacob wrote:
> > On Thu, Oct 31, 2002 at 12:04:16PM -0800, Matthew Jacob wrote:
> > > 
> > > *blush*
> > > 
> > > I was actually going to start finally working 2.5 next week (don't hit
> > > me! don't hit me)
> > 
> > Hehehe!  Going to start after the feature freeze is already over, makes it 
> > kind of hard to get anything new in doesn't it ;-)
> 
> Well, look- doing feature freezes early is all well and swell, but
> remember that a lot of us out here, if we get any work stuff at all for
> Linux, has us concentrate on 2.4, or even 2.2.

Yes, I know, that's why there was a wink-smiley there.

> driver subsystems are candidates for late binding and late changing
> because they are typically isolated areas.

As well as they are here.  At least driver updates anyway.  Driver 
subsystem changes are a bit harder to get in, especially if they stand a 
chance of breaking other working drivers.


-- 
  Doug Ledford <dledford@redhat.com>     919-754-3700 x44233
         Red Hat, Inc. 
         1801 Varsity Dr.
         Raleigh, NC 27606
  

Re: [PATCH] Ghost devices being reported with AIC7XXX version 6.2.6

[Mike Brown]

I'd rather have to add a list entry for one of a few dozen storage
array vendors then get hundreds bug reports from noname USB
block devices that blew up when we sent REPORT_LUNS.  Considering
a lot of them blow up if you ask for more than a 36 byte INQUIRY
response, I think REPORT_LUNS should be special cased in the
blacklist.

I haven't been tracking 2.5, but I knew there were plans to push
push the scanning code and the blacklist stuff into a userspace
scsid.  Did this make it?

On Thu, Oct 31, 2002 at 12:41:50PM -0800, Matthew Jacob wrote:
> 
> Yeah, but lets get out of the tailchasing exercise of list updates if we
> can...
> 
> 
> > > And we recently added INQUIRY with the EVPD bit set and an EVPD page 0.  
> > > >From the reports I've seen, I'm pretty sure it's causing a more than
> > > trivial number of devices to lock up on boot.  I suspect blindly pulling a
> > > REPORT_LUNS on SCSI-2 devices would likely cause similar problems.
> > 
> > What about adding BLIST_FORCE_REPORT_LUNS?
> > 
> > -Michael F. Brown, EMC Corp.
> > 
> > Email:            mbrown@emc.com
> > EMC Tie Line:             x43416
> > External Line:    (508) 249-3416
> > 
> > "5 years from now everyone will be running free
> >  GNU on their 200 MIPS, 64M SPARCstation-5."      -Andrew Tanenbaum '92
> > 
> > (In late 1997 I installed Linux for the first time on my 200Mhz, 128M
> >  AMD x86 clone)
> > 
-Michael F. Brown, EMC Corp.

Email:            mbrown@emc.com
EMC Tie Line:             x43416
External Line:    (508) 249-3416

"5 years from now everyone will be running free
 GNU on their 200 MIPS, 64M SPARCstation-5."      -Andrew Tanenbaum '92

(In late 1997 I installed Linux for the first time on my 200Mhz, 128M
 AMD x86 clone)

Re: [PATCH] Ghost devices being reported with AIC7XXX version 6.2.6

[James Bottomley]

mbrown@emc.com said:
> I haven't been tracking 2.5, but I knew there were plans to push push
> the scanning code and the blacklist stuff into a userspace scsid.  Did
> this make it? 

That was my plan, but I spent too much time scraping out the innards.  I hope 
to do it for 2.7

James

Re: [PATCH] Ghost devices being reported with AIC7XXX version 6.2.6

[Doug Ledford]

On Thu, Oct 31, 2002 at 03:38:57PM -0500, Mike Brown wrote:
> Hi,
> 
> > The whole "support more than 8 luns on SCSI-2 devices" is a hack anyway, I 
> > would be more likely to just remove it instead of changing other things.
> 
> This would break production environments.  Symmetrix isn't the only
> storage array that supports this hack.  DG, Dell, HP, and others also
> support this hack.  If its taken out in 2.5 and replaced with
> REPORT_LUNS that'd be ok, but taking it out of 2.4 without replacing
> it with REPORT_LUNS is going to break people.

Note, these hacks have caused more more bug reports and more crap in the 
last 2 years than anything else when it comes to device scanning in linux.  
If it were up to me, I'm so fed up with them I'd yank *all* the hacks that 
make us scan for non-compliant devices and instead tell the vendors to fix 
their firmware to be SCSI compliant.

> > > 3) Linux should be using the Report Luns command to determine how
> > >    many luns are on a device and at what locations.  This might
> > >    even allow you to never probe more than 8 luns on a SCSI 2
> > >    device unless they support this command.  Does the Symetrix support
> > >    it?  Going beyond 8 luns on a SCSI2 device is really a hack
> > >    otherwise.
> > 
> > We currently only do report luns on SCSI-3 devices.  I didn't think this 
> > was a supported command on SCSI-2, but I hadn't checked the spec 
> > recently...hmmm...nope, not supported in SCSI-2, so using report luns on 
> > SCSI-2 devices is just as much a hack as going above lun 7 on SCSI-2 
> > devices without specific knowledge of transfer interconnect.
> 
> Symmetrix supports Report Luns despite reporting SCSI_2 Units.  The

Can you comment on why Symmetrix reports SCSI-2 units then?  Report Luns
is an optional SCSI-3 command.  If you don't have all the required SCSI-3
items implemented yet so that you can't report SCSI-3, then I would think
you need to not worry about optional commands until the required ones are
done.  On the other hand, if you've got all the required SCSI-3 items
implemented, then why aren't you reporting SCSI-3?

>  I don't know
> what the right fix is for 2.4.  We need a hack akin to something like:

The right fix doesn't exist.  Hack is exactly what it's going to take to 
fix this.  Once again, it's a case of some vendor wanting SCSI-3 features 
on a device that they only report as being SCSI-2 causing breakage.

I'm currently working in 2.5, not 2.4.  This will be fixed in 2.5 by using 
report luns.  My goal for 2.5 is to make the whitelist as small as 
possible though, so fixing up your firmware to report the proper SCSI 
version would be appreciated.  If not, then it will have to be a report 
luns whitelist entry.  For 2.4, I don't have an answer and I'm not sure 
when I would get around to looking at it personally.  Not this week 
anyway, maybe next.

-- 
  Doug Ledford <dledford@redhat.com>     919-754-3700 x44233
         Red Hat, Inc. 
         1801 Varsity Dr.
         Raleigh, NC 27606
  

Re: [PATCH] Ghost devices being reported with AIC7XXX version 6.2.6

[Patrick Mansfield]

On Thu, Oct 31, 2002 at 07:21:12PM +0000, Alan Cox wrote:
> On Thu, 2002-10-31 at 18:28, Matthew Jacob wrote:
> > > 3) Linux should be using the Report Luns command to determine how
> > >    many luns are on a device and at what locations.  This might
> > >    even allow you to never probe more than 8 luns on a SCSI 2
> > >    device unless they support this command.  Does the Symetrix support
> > >    it?  Going beyond 8 luns on a SCSI2 device is really a hack
> > >    otherwise.
> > 
> > Absolutely.
> 
> Now is the right time to fix this properly for 2.5

REPORT LUNS is a SCSI-3 command, not SCSI-2, so it can't solve
the problem. Right?

You should be able to configure any recent EMC box (and AFAIK any
recent disk array hardware, at least IBM Shark, IBM fastt) to report
back as a SCSI-3 device.

-- Patrick Mansfield

Re: [PATCH] Ghost devices being reported with AIC7XXX version 6.2.6

[Alan Cox]

On Thu, 2002-10-31 at 20:17, Doug Ledford wrote:
> On Thu, Oct 31, 2002 at 12:04:16PM -0800, Matthew Jacob wrote:
> > 
> > *blush*
> > 
> > I was actually going to start finally working 2.5 next week (don't hit
> > me! don't hit me)
> 
> Hehehe!  Going to start after the feature freeze is already over, makes it 
> kind of hard to get anything new in doesn't it ;-)

Its not a major new feature its just some more scsi bug fixing