Re: [Xen-devel] [RFC PATCH] Data integrity extension support for xen-block

[David Vrabel <david.vrabel@xxxxxxxxxx>]

On 08/04/16 15:20, Ian Jackson wrote:
> David Vrabel writes ("Re: [RFC PATCH] Data integrity extension support for 
> xen-block"):
>> You need to read the relevant SCSI specification and find out what
>> interfaces and behaviour the hardware has so you can specify compatible
>> interfaces in blkif.
>>
>> My (brief) reading around this suggests that the integrity data has a
>> specific format (a CRC of some form) and the integrity data written for
>> sector S and retrieved verbatim when sector S is re-read.
> 
> I think it's this:
> 
> https://en.wikipedia.org/wiki/Data_Integrity_Field
> https://www.kernel.org/doc/Documentation/block/data-integrity.txt
> 
> In which case AFAICT the format is up to the guest (ie the operating
> system or file system) and it's opaque to the host (the storage) -
> unless the guest consents, of course.

I disagree, but I can't work out where to get the relevant T10 PI/DIF
spec from to provide an authoritative link[1].  The DI metadata has as a
set of well defined format, most of which include a 16-bit GUARD CRC, a
32 bit REFERENCE tag and 16 bit for user defined usage.

The application cannot use all the bits for its own use since the
hardware may check the GUARD and REFERENCE tags itself.

David

[0] Try: https://www.usenix.org/legacy/event/lsf07/tech/petersen.pdf

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