NAA breakage

Hello folks,

I'd like to reopen this discussion because there was no conclusion in last three weeks and I still believe that the present implementation of NAA IDs is wrong, regardless of the Andy's Shevchenko patch. Let me explain why:

(1) According to SCSI SPC-3 (7.6.10), 0x80 VPD unit serial number is a vendor-assigned variable-length string of ASCII data with characters 20h through 7Eh.

(2) target_emulate_evpd_83() wrongly assumes that the unit serial number is a hex-encoded string with at least 25 characters and generates NAA ID using hex2bin() from its first 25 chars.

(3) SCSI SPC-3 (7.6.3.6.4) states that NAA IEEE Registered Extended identifier is a 16-byte fixed-length binary sequence that is _uniquely_ assigned by the organization associated with the IEEE company_id (LIO uses OpenFabrics IEEE ID 00 14 05). That is, NAA ID must be a guaranteed _stable_ worldwide-unique identifier and e.g. VMware strongly relies on this.

From (1) and (2) it follows me that LIO does not guarantee the
uniqueness and in fact it very easily produces duplicate NAA IDs. For example, unit serial numbers with a common 25-character prefix will necessarily lead to the same NAA ID.

With Andy's Shevchenko patch, the
same also holds for serial numbers that contain only non-hex characters in first 25 bytes, resulting in NAA IDs full of 0xff. And there are other cases where hex2bin() conversion applied to serial numbers leads to duplicates.

So the way NAA ID is generated from the serial number seems to be broken and does not guarantee NAA ID uniqueness even if the serial numbers are unique and SPC-3 compliant.

However, I think that the solution is easy:

(a) Provide a ConfigFS entry for NAA ID to allow userspace to maintain the uniqueness on its own.

(b) If no ConfigFS NAA ID is specified, target_emulate_evpd_83() should make the best effort to generate unique NAA ID from the unit serial number. An obvious solution is to compute a hash (e.g. SHA1) from the unit serial number and use its 13 most significant bytes to fill vendor-specific NAA ID bytes.

Yes, the drawback is that such a change breaks NAA IDs of existing setups. It's a question if it is better to maintain backward compatibility, or fix it while LIO is in mainline for a short time yet.

Quoted 7 lines

Hello folks,

I'd like to reopen this discussion because there was no conclusion in last three weeks and I still believe that the present implementation of NAA IDs is wrong, regardless of the Andy's Shevchenko patch. Let me explain why:

Hi Martin,

Thanks for your follow-up here Martin. Getting this resolved for v3.1 is still on my todo list, and the patch I would like to push will be ready for review in the next days. My thoughts on your comments are below.

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(1) According to SCSI SPC-3 (7.6.10), 0x80 VPD unit serial number is a vendor-assigned variable-length string of ASCII data with characters 20h through 7Eh.

Correct

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(2) target_emulate_evpd_83() wrongly assumes that the unit serial number is a hex-encoded string with at least 25 characters and generates NAA ID using hex2bin() from its first 25 chars.

Correct, the fix that I think makes the most sense here is to ensure that the unit serial number always contains only hex digits (by stripping out the non hex charactes) when set via configfs in vpd_unit_serial.

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(3) SCSI SPC-3 (7.6.3.6.4) states that NAA IEEE Registered Extended identifier is a 16-byte fixed-length binary sequence that is _uniquely_ assigned by the organization associated with the IEEE company_id (LIO uses OpenFabrics IEEE ID 00 14 05). That is, NAA ID must be a guaranteed _stable_ worldwide-unique identifier and e.g. VMware strongly relies on this.

From (1) and (2) it follows me that LIO does not guarantee the
uniqueness and in fact it very easily produces duplicate NAA IDs. For example, unit serial numbers with a common 25-character prefix will necessarily lead to the same NAA ID.

It's the job of userspace to generate a UUID for the unit_serial number, and to ensure (as much as possible) the UUID is unique. Taking the first 25 characters of this value has not created a problem so far. Can you give an example of how it's 'very easily' able to produce duplicate NAA IDs..?

Quoted 6 lines

With Andy's Shevchenko patch, the
same also holds for serial numbers that contain only non-hex characters in first 25 bytes, resulting in NAA IDs full of 0xff. And there are other cases where hex2bin() conversion applied to serial numbers leads to duplicates.

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So the way NAA ID is generated from the serial number seems to be broken and does not guarantee NAA ID uniqueness even if the serial numbers are unique and SPC-3 compliant.

However, I think that the solution is easy:

(a) Provide a ConfigFS entry for NAA ID to allow userspace to maintain the uniqueness on its own.

I am against exposing the NAA ID as a configfs attribute. I still think basing this upon the EVPD 0x80 unit serial still makes the most sense, and to make userspace ensure (as much as possible) that the UUID -> unit serial is unique.

Quoted 6 lines

(b) If no ConfigFS NAA ID is specified, target_emulate_evpd_83() should make the best effort to generate unique NAA ID from the unit serial number. An obvious solution is to compute a hash (e.g. SHA1) from the unit serial number and use its 13 most significant bytes to fill vendor-specific NAA ID bytes.

Generating a hash based upon unit serial for the vendor-specific NAA ID bytes might be useful, but I am still not convinced there is a real problem of duplicate NAA IDs using UUID based unit seriales for the vendor specific area..

Quoted 4 lines

Yes, the drawback is that such a change breaks NAA IDs of existing setups. It's a question if it is better to maintain backward compatibility, or fix it while LIO is in mainline for a short time yet.

I think the drawback is worth the extra pain here.. As mentioned, I am still leaning toward a simple fix to force hex characters for all vpd_unit_serial values set via configfs.

--nab

Hi Nicholas,

thanks for your response, see my comments below.

Dne 9.9.2011 23:38, Nicholas A. Bellinger napsal(a):

Quoted 1 line · Martin Svec

Quoted 5 lines

Quoted 5 lines

(2) target_emulate_evpd_83() wrongly assumes that the unit serial number is a hex-encoded string with at least 25 characters and generates NAA ID using hex2bin() from its first 25 chars.

Quoted 4 lines

Correct, the fix that I think makes the most sense here is to ensure that the unit serial number always contains only hex digits (by stripping out the non hex charactes) when set via configfs in vpd_unit_serial.

Martin: But then you place additional undocumented restrictions on the unit serial number format, don't you?

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(3) SCSI SPC-3 (7.6.3.6.4) states that NAA IEEE Registered Extended identifier is a 16-byte fixed-length binary sequence that is _uniquely_ assigned by the organization associated with the IEEE company_id (LIO uses OpenFabrics IEEE ID 00 14 05). That is, NAA ID must be a guaranteed _stable_ worldwide-unique identifier and e.g. VMware strongly relies on this.

From (1) and (2) it follows me that LIO does not guarantee the
uniqueness and in fact it very easily produces duplicate NAA IDs. For example, unit serial numbers with a common 25-character prefix will necessarily lead to the same NAA ID.

Quoted 5 lines

It's the job of userspace to generate a UUID for the unit_serial number, and to ensure (as much as possible) the UUID is unique. Taking the first 25 characters of this value has not created a problem so far. Can you give an example of how it's 'very easily' able to produce duplicate NAA IDs..?

Martin: Again, SPC-3 says nothing about hex-character UUID as a unit serial number. That's the key point I try to emphasize -- you assume that it has a particular format but everbody who follows only the SPC-3 specification and doesn't know these LIO-specific restrictions risks duplicate NAA IDs.

Below is an example of two unique SPC-3
compliant serial numbers that result in the same NAA ID (tested with mainline kernel 3.1.0-rc1+):

$ sg_inq -p 0x83 /dev/sdc
VPD INQUIRY: Device Identification page
   Designation descriptor number 1, descriptor length: 20
     designator_type: NAA,  code_set: Binary
     associated with the addressed logical unit
       NAA 6, IEEE Company_id: 0x140f
       Vendor Specific Identifier: 0xfefbfef9f
       Vendor Specific Identifier Extension: 0xefefcfbfefef9fef
       [0x600140ffefbfef9fefefcfbfefef9fef]
   Designation descriptor number 2, descriptor length: 78
     designator_type: T10 vendor identification,  code_set: ASCII
     associated with the addressed logical unit
       vendor id: LIO-ORG
       vendor specific: 
IBLOCK:OurCompanyProductionSAN.StorageServer12.Customer524.Drive1

$ sg_inq -p 0x83 /dev/sdd
VPD INQUIRY: Device Identification page
   Designation descriptor number 1, descriptor length: 20
     designator_type: NAA,  code_set: Binary
     associated with the addressed logical unit
       NAA 6, IEEE Company_id: 0x140f
       Vendor Specific Identifier: 0xfefbfef9f
       Vendor Specific Identifier Extension: 0xefefcfbfefef9fef
       [0x600140ffefbfef9fefefcfbfefef9fef]
   Designation descriptor number 2, descriptor length: 78
     designator_type: T10 vendor identification,  code_set: ASCII
     associated with the addressed logical unit
       vendor id: LIO-ORG
       vendor specific: 
IBLOCK:OurCompanyProductionSAN.StorageServer12.Customer524.Drive2

Clearly, the serial numbers differ only in the last character (drive number), far beyond the 25 characters used for NAA. For somebody that starts with (i)SCSI and wants a unique and readable identification of its LUNs, these serial numbers IMHO perfectly make sense, are SPC-3 compliant, but VMware vSphere will be totally confused of their NAAs generated by LIO.

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However, I think that the solution is easy:

(a) Provide a ConfigFS entry for NAA ID to allow userspace to maintain the uniqueness on its own.

I am against exposing the NAA ID as a configfs attribute. I still think basing this upon the EVPD 0x80 unit serial still makes the most sense, and to make userspace ensure (as much as possible) that the UUID -> unit serial is unique.

Quoted 6 lines

(b) If no ConfigFS NAA ID is specified, target_emulate_evpd_83() should make the best effort to generate unique NAA ID from the unit serial number. An obvious solution is to compute a hash (e.g. SHA1) from the unit serial number and use its 13 most significant bytes to fill vendor-specific NAA ID bytes.

Generating a hash based upon unit serial for the vendor-specific NAA ID bytes might be useful, but I am still not convinced there is a real problem of duplicate NAA IDs using UUID based unit seriales for the vendor specific area..

Quoted 8 lines

Quoted 4 lines

Yes, the drawback is that such a change breaks NAA IDs of existing setups. It's a question if it is better to maintain backward compatibility, or fix it while LIO is in mainline for a short time yet.

I think the drawback is worth the extra pain here.. As mentioned, I am still leaning toward a simple fix to force hex characters for all vpd_unit_serial values set via configfs.

Martin: Yes, that's a possible solution -- enforce vpd_unit_serial to be a hex-character string at least 25 characters long, and document that the first 25 characters must be unique within a given SAN. It's more restrictive than SPC-3 says but at least it doesn't allow to set vpd_unit_serial to something that leads to duplicate NAA IDs.

I still think that my proposal is better because it provides the same guarantees without additional restrictions to SPC-3 standard but I can live with it :-) All that I want is to save future LIO users from surprises caused by the NAA ID generation based on undocumented vpd_unit_serial assumptions.

Quoted 6 lines

Hi Nicholas,

thanks for your response, see my comments below.

Dne 9.9.2011 23:38, Nicholas A. Bellinger napsal(a):

Quoted 1 line · Martin Svec

<SNIP>

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Quoted 8 lines

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(2) target_emulate_evpd_83() wrongly assumes that the unit serial number is a hex-encoded string with at least 25 characters and generates NAA ID using hex2bin() from its first 25 chars.

Correct, the fix that I think makes the most sense here is to ensure that the unit serial number always contains only hex digits (by stripping out the non hex charactes) when set via configfs in vpd_unit_serial.

Martin: But then you place additional undocumented restrictions on the unit serial number format, don't you?

No, it does not. It's vendor specific and perfectly within what's allowable as defined by SPC-3.

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(3) SCSI SPC-3 (7.6.3.6.4) states that NAA IEEE Registered Extended identifier is a 16-byte fixed-length binary sequence that is _uniquely_ assigned by the organization associated with the IEEE company_id (LIO uses OpenFabrics IEEE ID 00 14 05). That is, NAA ID must be a guaranteed _stable_ worldwide-unique identifier and e.g. VMware strongly relies on this.

From (1) and (2) it follows me that LIO does not guarantee the
uniqueness and in fact it very easily produces duplicate NAA IDs. For example, unit serial numbers with a common 25-character prefix will necessarily lead to the same NAA ID.

Quoted 5 lines

It's the job of userspace to generate a UUID for the unit_serial number, and to ensure (as much as possible) the UUID is unique. Taking the first 25 characters of this value has not created a problem so far. Can you give an example of how it's 'very easily' able to produce duplicate NAA IDs..?

Quoted 5 lines

Martin: Again, SPC-3 says nothing about hex-character UUID as a unit serial number. That's the key point I try to emphasize -- you assume that it has a particular format but everbody who follows only the SPC-3 specification and doesn't know these LIO-specific restrictions risks duplicate NAA IDs.

Not exactly. When it doubt, people need to follow the offical userspace code. I am happy to support people who insist on their own interface to configfs, but for something like this your code needs to follow what our existing userspace library does to ensure uniqueness.

Quoted 20 lines

Below is an example of two unique SPC-3
compliant serial numbers that result in the same NAA ID (tested with mainline kernel 3.1.0-rc1+):

$ sg_inq -p 0x83 /dev/sdc
VPD INQUIRY: Device Identification page
    Designation descriptor number 1, descriptor length: 20
      designator_type: NAA,  code_set: Binary
      associated with the addressed logical unit
        NAA 6, IEEE Company_id: 0x140f
        Vendor Specific Identifier: 0xfefbfef9f
        Vendor Specific Identifier Extension: 0xefefcfbfefef9fef
        [0x600140ffefbfef9fefefcfbfefef9fef]
    Designation descriptor number 2, descriptor length: 78
      designator_type: T10 vendor identification,  code_set: ASCII
      associated with the addressed logical unit
        vendor id: LIO-ORG
        vendor specific:
IBLOCK:OurCompanyProductionSAN.StorageServer12.Customer524.Drive1

Quoted 17 lines

$ sg_inq -p 0x83 /dev/sdd
VPD INQUIRY: Device Identification page
    Designation descriptor number 1, descriptor length: 20
      designator_type: NAA,  code_set: Binary
      associated with the addressed logical unit
        NAA 6, IEEE Company_id: 0x140f
        Vendor Specific Identifier: 0xfefbfef9f
        Vendor Specific Identifier Extension: 0xefefcfbfefef9fef
        [0x600140ffefbfef9fefefcfbfefef9fef]
    Designation descriptor number 2, descriptor length: 78
      designator_type: T10 vendor identification,  code_set: ASCII
      associated with the addressed logical unit
        vendor id: LIO-ORG
        vendor specific:
IBLOCK:OurCompanyProductionSAN.StorageServer12.Customer524.Drive2

FYI, descriptor number 2 above this is the 0x83 T10 vendor ID, and not the 0x80 unit serial number.

Quoted 6 lines

Clearly, the serial numbers differ only in the last character (drive number), far beyond the 25 characters used for NAA. For somebody that starts with (i)SCSI and wants a unique and readable identification of its LUNs, these serial numbers IMHO perfectly make sense, are SPC-3 compliant, but VMware vSphere will be totally confused of their NAAs generated by LIO.

This is broken userspace code that is using the unit serial number for informational purposes. Please don't do this.

All of the lio-utils and rtslib userspace generate a uuid for the unit serial number, and do not have an issue with the scenario you are describing. This is what your userspace should be doing as well.

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However, I think that the solution is easy:

(a) Provide a ConfigFS entry for NAA ID to allow userspace to maintain the uniqueness on its own.

I am against exposing the NAA ID as a configfs attribute. I still think basing this upon the EVPD 0x80 unit serial still makes the most sense,
and to make userspace ensure (as much as possible) that the UUID -> unit
serial is unique.

Quoted 6 lines

(b) If no ConfigFS NAA ID is specified, target_emulate_evpd_83() should make the best effort to generate unique NAA ID from the unit serial number. An obvious solution is to compute a hash (e.g. SHA1) from the unit serial number and use its 13 most significant bytes to fill vendor-specific NAA ID bytes.

Generating a hash based upon unit serial for the vendor-specific NAA ID bytes might be useful, but I am still not convinced there is a real problem of duplicate NAA IDs using UUID based unit seriales for the vendor specific area..

Quoted 8 lines

Quoted 4 lines

Yes, the drawback is that such a change breaks NAA IDs of existing setups. It's a question if it is better to maintain backward compatibility, or fix it while LIO is in mainline for a short time yet.

I think the drawback is worth the extra pain here.. As mentioned, I am still leaning toward a simple fix to force hex characters for all vpd_unit_serial values set via configfs.

Martin: Yes, that's a possible solution -- enforce vpd_unit_serial to be a hex-character string at least 25 characters long, and document that the first 25 characters must be unique within a given SAN. It's more restrictive than SPC-3 says but at least it doesn't allow to set vpd_unit_serial to something that leads to duplicate NAA IDs.

Quoted 6 lines

I still think that my proposal is better because it provides the same guarantees without additional restrictions to SPC-3 standard but I can live with it :-) All that I want is to save future LIO users from surprises caused by the NAA ID generation based on undocumented vpd_unit_serial assumptions.

No, changing kernel code to address the breakage of your own userspace is not an option here.

Please fix your userspace code to follow what rtslib has always done to ensure the uniqueness of vpd_unit_serial via a well known method (eg:
uuid).

http://www.risingtidesystems.com/git/?p=rtslib.git;a=blob;f=rtslib/tcm.py;h=4da49b0f4a4aea9a1eebed23d457181085a2d03d;hb=HEAD#l307

Thanks,

--nab

thanks a lot for your comments. Clearly there was a misunderstanding of who is the vendor that defines what is "vendor-specific" in case of LIO. Of course, it is easy for me to fix my userspace code to generate serial numbers without these issues. But I suggest to enforce vpd_unit_serial restrictions in configfs code because rtslib/lio-utils is just a referential userspace implementation, not a kernel ABI.

Quoted 6 lines · Martin Svec

thanks a lot for your comments. Clearly there was a misunderstanding of who is the vendor that defines what is "vendor-specific" in case of LIO. Of course, it is easy for me to fix my userspace code to generate serial numbers without these issues. But I suggest to enforce vpd_unit_serial restrictions in configfs code because rtslib/lio-utils is just a referential userspace implementation, not a kernel ABI.

I feel it's time to add my 2 cents to this discussion. A vendor-specific identifier in my mind could very well be what Martin uses it for, in my opinion - at least according to SPC-3.

If the LIO stack cannot handle
such use of identifiers the configfs code should refuse to accept such an identifier. If for example the LIO code only creates a valid NAA/WWN from a hex string of a certain length, it should only accept a hex string of that length. It should not be a requirement to exactly follow what rtslib does in every case.

Of course the way I see it the vendor specific identifier doesn't necessarily have anything to do with the NAA/WWN, so it would be nice if one could set both a WWN as a hex string of the correct length and format, and a vendor-specific string in a mostly freeform manner as long as it abides by SPC-3. The WWN shouldn't necessarily be generated from the vendor identifier.