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

[Bob Liu <bob.liu@oracle.com>]

On 04/07/2016 06:00 PM, 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.
> 
> Welcome any better ideas, thank you!
> 

A simpler possible solution:

bob@boliuliu:~/xen$ git diff xen/include/public/io/blkif.h
diff --git a/xen/include/public/io/blkif.h b/xen/include/public/io/blkif.h
index 3d8d39f..34581a5 100644
--- a/xen/include/public/io/blkif.h
+++ b/xen/include/public/io/blkif.h
@@ -689,6 +689,11 @@ struct blkif_request_segment {
 struct blkif_request {
     uint8_t        operation;    /* BLKIF_OP_???                         */
     uint8_t        nr_segments;  /* number of segments                   */
+    /*
+     * Recording how many segments are data integrity segments.
+     * raw data_segments + dix_segments = nr_segments
+     */
+    uint8_t       dix_segments;
     blkif_vdev_t   handle;       /* only for read/write requests         */
     uint64_t       id;           /* private guest value, echoed in resp  */
     blkif_sector_t sector_number;/* start sector idx on disk (r/w only)  */
@@ -715,6 +720,11 @@ struct blkif_request_indirect {
     uint8_t        operation;    /* BLKIF_OP_INDIRECT                    */
     uint8_t        indirect_op;  /* BLKIF_OP_{READ/WRITE}                */
     uint16_t       nr_segments;  /* number of segments                   */
+    /*
+     * Recording how many segments are data integrity segments.
+     * raw data_segments + dix_segments = nr_segments
+     */
+    uint16_t       dix_segments;
     uint64_t       id;           /* private guest value, echoed in resp  */
     blkif_sector_t sector_number;/* start sector idx on disk (r/w only)  */
     blkif_vdev_t   handle;       /* same as for read/write requests      */

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