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

[David Vrabel <david.vrabel@xxxxxxxxxx>]

On 07/04/16 11:00, Bob Liu wrote:
> * What's data integrity extension and why?
> Modern filesystems feature checksumming of data and metadata to protect 
> against
> data corruption.  However, the detection of the corruption is done at read 
> time
> which could potentially be months after the data was written.  At that point 
> the
> original data that the application tried to write is most likely lost.
> 
> The solution in Linux is the data integrity framework which enables protection
> information to be pinned to I/Os and sent to/received from controllers that
> support it. struct bio has been extended with a pointer to a struct bip which
> in turn contains the integrity metadata. The bip is essentially a trimmed down
> bio with a bio_vec and some housekeeping.
> 
> * Issues when xen-block get involved.
> xen-blkfront only transmits the normal data of struct bio while the integrity
> metadata buffer(struct bio_integrity_payload in each bio) is ignored.
> 
> * Proposal of transmitting bio integrity payload.
> Adding an extra request following the normal data request, this extra request
> contains the integrity payload.
> The xen-blkback will reconstruct an new bio with both received normal data and
> integrity metadata.

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.

David

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