SCSI persistent reservation terms

SCSI persistent reservation terms

[lemons_terry]

Hi

I'm trying to understand one aspect of the SCSI persistent reservation functionality. SPC-4 mentions the terms 'All Registrants' and 'Registrants Only', and applies these to both 'Write Exclusive' and 'Exclusive Access'.  Nowhere can I find a definition of what these terms mean.  If you would, please point me in the right direction.

Thanks!
tl

Terry Lemons
Backup Recovery Systems Division
EMC²
where information lives
4400 Computer Drive, MS D239
Westboro MA 01580
Phone: 508 898 7312
Email: Lemons_Terry@emc.com 



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Re: SCSI persistent reservation terms

[Nicholas A. Bellinger]

On Wed, 2010-04-07 at 10:55 -0400, lemons_terry@emc.com wrote:
> Hi
> 
> I'm trying to understand one aspect of the SCSI persistent reservation functionality.
> SPC-4 mentions the terms 'All Registrants' and 'Registrants Only', and applies these
> to both 'Write Exclusive' and 'Exclusive Access'.  Nowhere can I find a definition
> of what these terms mean.  If you would, please point me in the right direction.
> 

Greetings Terry,

'All Registrants' means that the persistent reservation holder is any
registstered I_T Nexus (eg: multiple reservation holders)

'Registrants Only' means that the persistent reservation holder is the
single registered I_T Nexus that has obtained the reservation via
RESERVE, PREEMPT, PREEMPT_AND_ABORT, or via another I_T Nexus with
REGISTER_AND_MOVE. (eg: single reservation holder)

You can find how this logic works for multi-fabric target mode by
grepping '_ALLREG' and '_REGONLY' in TCM code at:

http://git.kernel.org/?p=linux/kernel/git/nab/lio-core-2.6.git;a=blob;f=drivers/target/target_core_pr.c

Best,

--nab

RE: SCSI persistent reservation terms

[lemons_terry]

Hi

Thanks very much for the reply!  The difference between those terms make
sense now.

I took a look at these comments in the code:

303         switch (pr_reg_type) { 
304         case PR_TYPE_WRITE_EXCLUSIVE: 
305                 we = 1; 
306         case PR_TYPE_EXCLUSIVE_ACCESS: 
307                 /* 
308                  * Some commands are only allowed for the persistent
reservation 
309                  * holder. 
310                  */ 
311                 if (se_deve->deve_flags & DEF_PR_REGISTERED) 
312                         registered_nexus = 1; 
313                 break; 
314         case PR_TYPE_WRITE_EXCLUSIVE_REGONLY: 
315                 we = 1; 
316         case PR_TYPE_EXCLUSIVE_ACCESS_REGONLY: 
317                 /* 
318                  * Some commands are only allowed for registered I_T
Nexuses. 
319                  */ 
320                 reg_only = 1; 
321                 if (se_deve->deve_flags & DEF_PR_REGISTERED) 
322                         registered_nexus = 1; 
323                 break; 
324         case PR_TYPE_WRITE_EXCLUSIVE_ALLREG: 
325                 we = 1; 
326         case PR_TYPE_EXCLUSIVE_ACCESS_ALLREG: 
327                 /* 
328                  * Each registered I_T Nexus is a reservation
holder. 
329                  */ 
330                 all_reg = 1; 
331                 if (se_deve->deve_flags & DEF_PR_REGISTERED) 
332                         registered_nexus = 1; 
333                 break; 
334         default: 
335                 return -1; 
336         }

But I'm not able to devine the difference between 'write_exclusive' and
'write_exclusive_registrants_only'.  Given that a registration must
exist before a reservation can be done, what is the difference between
these two?  I just, again, looked for information describing these in
SPC-4, and didn't find any.

Thanks!
tl

-----Original Message-----
From: Nicholas A. Bellinger [mailto:nab@linux-iscsi.org] 
Sent: Wednesday, April 07, 2010 2:48 PM
To: Lemons, Terry
Cc: linux-scsi@vger.kernel.org
Subject: Re: SCSI persistent reservation terms

On Wed, 2010-04-07 at 10:55 -0400, lemons_terry@emc.com wrote:
> Hi
> 
> I'm trying to understand one aspect of the SCSI persistent reservation
functionality.
> SPC-4 mentions the terms 'All Registrants' and 'Registrants Only', and
applies these
> to both 'Write Exclusive' and 'Exclusive Access'.  Nowhere can I find
a definition
> of what these terms mean.  If you would, please point me in the right
direction.
> 

Greetings Terry,

'All Registrants' means that the persistent reservation holder is any
registstered I_T Nexus (eg: multiple reservation holders)

'Registrants Only' means that the persistent reservation holder is the
single registered I_T Nexus that has obtained the reservation via
RESERVE, PREEMPT, PREEMPT_AND_ABORT, or via another I_T Nexus with
REGISTER_AND_MOVE. (eg: single reservation holder)

You can find how this logic works for multi-fabric target mode by
grepping '_ALLREG' and '_REGONLY' in TCM code at:

http://git.kernel.org/?p=linux/kernel/git/nab/lio-core-2.6.git;a=blob;f=
drivers/target/target_core_pr.c

Best,

--nab

Re: SCSI persistent reservation terms

[Douglas Gilbert]

Are you looking at section 5.7 on Reservations in
SPC-4 (spc4r23.pdf)? Table 51 seems to address your
question.

Complex commands like Persistent Reservation In and Out
often have a brief explanation under the command entry.
However in earlier chapters (in this case "Model common
to all device types" (section 5)) important mechanisms
such as reservations are explained in more detail.
Also Annex B discusses the mapping between the newer
Persistent Reservation commands and the now obsolete
Reserve/Release commands.

Doug Gilbert


lemons_terry@emc.com wrote:
> Hi
> 
> Thanks very much for the reply!  The difference between those terms make
> sense now.
> 
> I took a look at these comments in the code:
> 
> 303         switch (pr_reg_type) { 
> 304         case PR_TYPE_WRITE_EXCLUSIVE: 
> 305                 we = 1; 
> 306         case PR_TYPE_EXCLUSIVE_ACCESS: 
> 307                 /* 
> 308                  * Some commands are only allowed for the persistent
> reservation 
> 309                  * holder. 
> 310                  */ 
> 311                 if (se_deve->deve_flags & DEF_PR_REGISTERED) 
> 312                         registered_nexus = 1; 
> 313                 break; 
> 314         case PR_TYPE_WRITE_EXCLUSIVE_REGONLY: 
> 315                 we = 1; 
> 316         case PR_TYPE_EXCLUSIVE_ACCESS_REGONLY: 
> 317                 /* 
> 318                  * Some commands are only allowed for registered I_T
> Nexuses. 
> 319                  */ 
> 320                 reg_only = 1; 
> 321                 if (se_deve->deve_flags & DEF_PR_REGISTERED) 
> 322                         registered_nexus = 1; 
> 323                 break; 
> 324         case PR_TYPE_WRITE_EXCLUSIVE_ALLREG: 
> 325                 we = 1; 
> 326         case PR_TYPE_EXCLUSIVE_ACCESS_ALLREG: 
> 327                 /* 
> 328                  * Each registered I_T Nexus is a reservation
> holder. 
> 329                  */ 
> 330                 all_reg = 1; 
> 331                 if (se_deve->deve_flags & DEF_PR_REGISTERED) 
> 332                         registered_nexus = 1; 
> 333                 break; 
> 334         default: 
> 335                 return -1; 
> 336         }
> 
> But I'm not able to devine the difference between 'write_exclusive' and
> 'write_exclusive_registrants_only'.  Given that a registration must
> exist before a reservation can be done, what is the difference between
> these two?  I just, again, looked for information describing these in
> SPC-4, and didn't find any.
> 
> Thanks!
> tl
> 
> -----Original Message-----
> From: Nicholas A. Bellinger [mailto:nab@linux-iscsi.org] 
> Sent: Wednesday, April 07, 2010 2:48 PM
> To: Lemons, Terry
> Cc: linux-scsi@vger.kernel.org
> Subject: Re: SCSI persistent reservation terms
> 
> On Wed, 2010-04-07 at 10:55 -0400, lemons_terry@emc.com wrote:
>> Hi
>>
>> I'm trying to understand one aspect of the SCSI persistent reservation
> functionality.
>> SPC-4 mentions the terms 'All Registrants' and 'Registrants Only', and
> applies these
>> to both 'Write Exclusive' and 'Exclusive Access'.  Nowhere can I find
> a definition
>> of what these terms mean.  If you would, please point me in the right
> direction.
> 
> Greetings Terry,
> 
> 'All Registrants' means that the persistent reservation holder is any
> registstered I_T Nexus (eg: multiple reservation holders)
> 
> 'Registrants Only' means that the persistent reservation holder is the
> single registered I_T Nexus that has obtained the reservation via
> RESERVE, PREEMPT, PREEMPT_AND_ABORT, or via another I_T Nexus with
> REGISTER_AND_MOVE. (eg: single reservation holder)
> 
> You can find how this logic works for multi-fabric target mode by
> grepping '_ALLREG' and '_REGONLY' in TCM code at:
> 
> http://git.kernel.org/?p=linux/kernel/git/nab/lio-core-2.6.git;a=blob;f=
> drivers/target/target_core_pr.c
> 
> Best,
> 
> --nab
> 
> 
> 
> 
> --
> 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
> 

RE: SCSI persistent reservation terms

[lemons_terry]

Hi Doug

Thanks for the reply.  I did stare at Table 51 before writing my email.
The 'Processing' language for the first and third rows is exactly the
same; that's why I'm still confused!

I've printed and read (several times) both section 5.7 'Reservations'
and sections 6.13 'PERSISTENT RESERVE IN' / 6.14 'PERSISTENT RESERVE
OUT'.  But I don't see any language that explains the difference between
'write_exclusive' and 'write_exclusive_registrants_only'.  If this is in
there, I apologize for not seeing it.

Thanks
tl

-----Original Message-----
From: Douglas Gilbert [mailto:dgilbert@interlog.com] 
Sent: Monday, April 12, 2010 9:55 AM
To: Lemons, Terry
Cc: nab@linux-iscsi.org; linux-scsi@vger.kernel.org
Subject: Re: SCSI persistent reservation terms

Are you looking at section 5.7 on Reservations in
SPC-4 (spc4r23.pdf)? Table 51 seems to address your
question.

Complex commands like Persistent Reservation In and Out
often have a brief explanation under the command entry.
However in earlier chapters (in this case "Model common
to all device types" (section 5)) important mechanisms
such as reservations are explained in more detail.
Also Annex B discusses the mapping between the newer
Persistent Reservation commands and the now obsolete
Reserve/Release commands.

Doug Gilbert


lemons_terry@emc.com wrote:
> Hi
> 
> Thanks very much for the reply!  The difference between those terms
make
> sense now.
> 
> I took a look at these comments in the code:
> 
> 303         switch (pr_reg_type) { 
> 304         case PR_TYPE_WRITE_EXCLUSIVE: 
> 305                 we = 1; 
> 306         case PR_TYPE_EXCLUSIVE_ACCESS: 
> 307                 /* 
> 308                  * Some commands are only allowed for the
persistent
> reservation 
> 309                  * holder. 
> 310                  */ 
> 311                 if (se_deve->deve_flags & DEF_PR_REGISTERED) 
> 312                         registered_nexus = 1; 
> 313                 break; 
> 314         case PR_TYPE_WRITE_EXCLUSIVE_REGONLY: 
> 315                 we = 1; 
> 316         case PR_TYPE_EXCLUSIVE_ACCESS_REGONLY: 
> 317                 /* 
> 318                  * Some commands are only allowed for registered
I_T
> Nexuses. 
> 319                  */ 
> 320                 reg_only = 1; 
> 321                 if (se_deve->deve_flags & DEF_PR_REGISTERED) 
> 322                         registered_nexus = 1; 
> 323                 break; 
> 324         case PR_TYPE_WRITE_EXCLUSIVE_ALLREG: 
> 325                 we = 1; 
> 326         case PR_TYPE_EXCLUSIVE_ACCESS_ALLREG: 
> 327                 /* 
> 328                  * Each registered I_T Nexus is a reservation
> holder. 
> 329                  */ 
> 330                 all_reg = 1; 
> 331                 if (se_deve->deve_flags & DEF_PR_REGISTERED) 
> 332                         registered_nexus = 1; 
> 333                 break; 
> 334         default: 
> 335                 return -1; 
> 336         }
> 
> But I'm not able to devine the difference between 'write_exclusive'
and
> 'write_exclusive_registrants_only'.  Given that a registration must
> exist before a reservation can be done, what is the difference between
> these two?  I just, again, looked for information describing these in
> SPC-4, and didn't find any.
> 
> Thanks!
> tl
> 
> -----Original Message-----
> From: Nicholas A. Bellinger [mailto:nab@linux-iscsi.org] 
> Sent: Wednesday, April 07, 2010 2:48 PM
> To: Lemons, Terry
> Cc: linux-scsi@vger.kernel.org
> Subject: Re: SCSI persistent reservation terms
> 
> On Wed, 2010-04-07 at 10:55 -0400, lemons_terry@emc.com wrote:
>> Hi
>>
>> I'm trying to understand one aspect of the SCSI persistent
reservation
> functionality.
>> SPC-4 mentions the terms 'All Registrants' and 'Registrants Only',
and
> applies these
>> to both 'Write Exclusive' and 'Exclusive Access'.  Nowhere can I find
> a definition
>> of what these terms mean.  If you would, please point me in the right
> direction.
> 
> Greetings Terry,
> 
> 'All Registrants' means that the persistent reservation holder is any
> registstered I_T Nexus (eg: multiple reservation holders)
> 
> 'Registrants Only' means that the persistent reservation holder is the
> single registered I_T Nexus that has obtained the reservation via
> RESERVE, PREEMPT, PREEMPT_AND_ABORT, or via another I_T Nexus with
> REGISTER_AND_MOVE. (eg: single reservation holder)
> 
> You can find how this logic works for multi-fabric target mode by
> grepping '_ALLREG' and '_REGONLY' in TCM code at:
> 
>
http://git.kernel.org/?p=linux/kernel/git/nab/lio-core-2.6.git;a=blob;f=
> drivers/target/target_core_pr.c
> 
> Best,
> 
> --nab
> 
> 
> 
> 
> --
> 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
> 

RE: SCSI persistent reservation terms

[James Bottomley]

On Mon, 2010-04-12 at 10:53 -0400, lemons_terry@emc.com wrote:
> Hi Doug
> 
> Thanks for the reply.  I did stare at Table 51 before writing my email.
> The 'Processing' language for the first and third rows is exactly the
> same; that's why I'm still confused!
> 
> I've printed and read (several times) both section 5.7 'Reservations'
> and sections 6.13 'PERSISTENT RESERVE IN' / 6.14 'PERSISTENT RESERVE
> OUT'.  But I don't see any language that explains the difference between
> 'write_exclusive' and 'write_exclusive_registrants_only'.  If this is in
> there, I apologize for not seeing it.

The change is in the definition of the "reservation holder" for the
reservation (5.7.10).  For exclusive all registrants reservations, the
holder is all registered initiators; otherwise it's the initiator port
the reservation was issued on.

James