This adds optional integrity functions for given bio, they are
passsed to bio_integrity_prep and initialized in
bio_integrity_payload.
The optional integrity generate/verify functions take priority
over the ones registered on the block device.

It brings flexibility to bio integrity handling. e.g. a network
filesystem with integrity support would have integrity
generation happen on the clients, and send them over the wire.
On the server side once we receive the integrity bits and pass
the network layer checksums we would merely pass it on to the
block devices have integrity support, so we don't have to
calculate the integrity again.
Verification shares the same principle: on the server we just
copy the integrity bits from the device and send them through
the wire, then the verification happens on the clients.

Index: linux-3.10.0-862.9.1.el7/fs/bio-integrity.c
===================================================================
--- linux-3.10.0-862.9.1.el7.orig/fs/bio-integrity.c
+++ linux-3.10.0-862.9.1.el7/fs/bio-integrity.c
@@ -38,7 +38,7 @@ void blk_flush_integrity(void)
 }
 
 /**
- * bio_integrity_alloc - Allocate integrity payload and attach it to bio
+ * bio_integrity_alloc_fn - Allocate integrity payload and attach it to bio
  * @bio:	bio to attach integrity metadata to
  * @gfp_mask:	Memory allocation mask
  * @nr_vecs:	Number of integrity metadata scatter-gather elements
@@ -47,9 +47,11 @@ void blk_flush_integrity(void)
  * metadata.  nr_vecs specifies the maximum number of pages containing
  * integrity metadata that can be attached.
  */
-struct bio_integrity_payload *bio_integrity_alloc(struct bio *bio,
-						  gfp_t gfp_mask,
-						  unsigned int nr_vecs)
+struct bio_integrity_payload *bio_integrity_alloc_fn(struct bio *bio,
+						     gfp_t gfp_mask,
+						     unsigned int nr_vecs,
+						     integrity_gen_fn *generate_fn,
+						     integrity_vrfy_fn *verify_fn)
 {
 	struct bio_integrity_payload *bip;
 	struct bio_set *bs = bio->bi_pool;
@@ -81,6 +83,8 @@ struct bio_integrity_payload *bio_integr
 
 	bip->bip_slab = idx;
 	bip->bip_bio = bio;
+	bip->bip_generate_fn = generate_fn;
+	bip->bip_verify_fn = verify_fn;
 	bio->bi_integrity = bip;
 
 	return bip;
@@ -88,6 +92,13 @@ err:
 	mempool_free(bip, bs->bio_integrity_pool);
 	return NULL;
 }
+EXPORT_SYMBOL(bio_integrity_alloc_fn);
+
+struct bio_integrity_payload *bio_integrity_alloc(struct bio *bio, gfp_t gfp,
+						  unsigned int nr)
+{
+	return bio_integrity_alloc_fn(bio, gfp, nr, NULL, NULL);
+}
 EXPORT_SYMBOL(bio_integrity_alloc);
 
 /**
@@ -312,10 +323,12 @@ static void bio_integrity_generate(struc
 {
 	struct blk_integrity *bi = bdev_get_integrity(bio->bi_bdev);
 	struct blk_integrity_exchg bix;
+	struct bio_integrity_payload *bip = bio->bi_integrity;
 	struct bio_vec *bv;
 	sector_t sector = bio->bi_sector;
 	unsigned int i, sectors, total;
 	void *prot_buf = bio->bi_integrity->bip_buf;
+	integrity_gen_fn *generate_fn = bip->bip_generate_fn ?: bi->generate_fn;
 
 	total = 0;
 	bix.disk_name = bio->bi_bdev->bd_disk->disk_name;
@@ -328,7 +341,7 @@ static void bio_integrity_generate(struc
 		bix.prot_buf = prot_buf;
 		bix.sector = sector;
 
-		bi->generate_fn(&bix);
+		generate_fn(&bix);
 
 		sectors = bv->bv_len / bi->sector_size;
 		sector += sectors;
@@ -349,7 +362,7 @@ static inline unsigned short blk_integri
 }
 
 /**
- * bio_integrity_prep - Prepare bio for integrity I/O
+ * bio_integrity_prep_fn - Prepare bio for integrity I/O
  * @bio:	bio to prepare
  *
  * Description: Allocates a buffer for integrity metadata, maps the
@@ -359,7 +372,8 @@ static inline unsigned short blk_integri
  * block device's integrity function.  In the READ case, the buffer
  * will be prepared for DMA and a suitable end_io handler set up.
  */
-int bio_integrity_prep(struct bio *bio)
+int bio_integrity_prep_fn(struct bio *bio, integrity_gen_fn *generate_fn,
+			  integrity_vrfy_fn *verify_fn)
 {
 	struct bio_integrity_payload *bip;
 	struct blk_integrity *bi;
@@ -390,7 +404,8 @@ int bio_integrity_prep(struct bio *bio)
 	nr_pages = end - start;
 
 	/* Allocate bio integrity payload and integrity vectors */
-	bip = bio_integrity_alloc(bio, GFP_NOIO, nr_pages);
+	bip = bio_integrity_alloc_fn(bio, GFP_NOIO, nr_pages,
+				     generate_fn, verify_fn);
 	if (unlikely(bip == NULL)) {
 		printk(KERN_ERR "could not allocate data integrity bioset\n");
 		kfree(buf);
@@ -440,6 +455,12 @@ int bio_integrity_prep(struct bio *bio)
 
 	return 0;
 }
+EXPORT_SYMBOL(bio_integrity_prep_fn);
+
+int bio_integrity_prep(struct bio *bio)
+{
+	return bio_integrity_prep_fn(bio, NULL, NULL);
+}
 EXPORT_SYMBOL(bio_integrity_prep);
 
 /**
@@ -454,10 +475,13 @@ static int bio_integrity_verify(struct b
 {
 	struct blk_integrity *bi = bdev_get_integrity(bio->bi_bdev);
 	struct blk_integrity_exchg bix;
+	struct bio_integrity_payload *bip = bio->bi_integrity;
 	struct bio_vec *bv;
 	sector_t sector = bio->bi_integrity->bip_sector;
 	unsigned int i, sectors, total, ret;
 	void *prot_buf = bio->bi_integrity->bip_buf;
+	integrity_vrfy_fn *verify_fn = bip->bip_verify_fn ?:
+					bi->verify_fn;
 
 	ret = total = 0;
 	bix.disk_name = bio->bi_bdev->bd_disk->disk_name;
@@ -474,7 +498,7 @@ static int bio_integrity_verify(struct b
 		bix.prot_buf = prot_buf;
 		bix.sector = sector;
 
-		ret = bi->verify_fn(&bix);
+		ret = verify_fn(&bix);
 
 		if (ret) {
 			kunmap_atomic(kaddr);
@@ -711,7 +735,9 @@ int bio_integrity_clone(struct bio *bio,
 
 	BUG_ON(bip_src == NULL);
 
-	bip = bio_integrity_alloc(bio, gfp_mask, bip_src->bip_vcnt);
+	bip = bio_integrity_alloc_fn(bio, gfp_mask, bip_src->bip_vcnt,
+				     bip_src->bip_generate_fn,
+				     bip_src->bip_verify_fn);
 
 	if (bip == NULL)
 		return -EIO;
Index: linux-3.10.0-862.9.1.el7/include/linux/bio.h
===================================================================
--- linux-3.10.0-862.9.1.el7.orig/include/linux/bio.h
+++ linux-3.10.0-862.9.1.el7/include/linux/bio.h
@@ -195,6 +195,11 @@ struct bio_integrity_payload {
 	struct work_struct	bip_work;	/* I/O completion */
 
 	struct bio_vec		*bip_vec;
+
+	/* put after bip_vec as that is last externally-accessed bip_ field */
+	integrity_gen_fn	*bip_generate_fn;
+	integrity_vrfy_fn	*bip_verify_fn;
+ 
 	struct bio_vec		bip_inline_vecs[0];/* embedded bvec array */
 };
 #endif /* CONFIG_BLK_DEV_INTEGRITY */
@@ -618,6 +623,11 @@ struct biovec_slab {
 #define bio_integrity(bio) (bio->bi_integrity != NULL)
 
 extern struct bio_integrity_payload *bio_integrity_alloc(struct bio *, gfp_t, unsigned int);
+extern struct bio_integrity_payload *bio_integrity_alloc_fn(struct bio *bio,
+						gfp_t gfp_mask,
+						unsigned int nr_vecs,
+						integrity_gen_fn *generate_fn,
+						integrity_vrfy_fn *verify_fn);
 extern void bio_integrity_free(struct bio *);
 extern int bio_integrity_add_page(struct bio *, struct page *, unsigned int, unsigned int);
 extern int bio_integrity_enabled(struct bio *bio);
@@ -624,6 +634,9 @@ struct biovec_slab {
 extern int bio_integrity_set_tag(struct bio *, void *, unsigned int);
 extern int bio_integrity_get_tag(struct bio *, void *, unsigned int);
 extern int bio_integrity_prep(struct bio *);
+extern int bio_integrity_prep_fn(struct bio *bio,
+				 integrity_gen_fn *generate_fn,
+				 integrity_vrfy_fn *verify_fn);
 extern void bio_integrity_endio(struct bio *, int);
 extern void bio_integrity_advance(struct bio *, unsigned int);
 extern void bio_integrity_trim(struct bio *, unsigned int, unsigned int);
Index: linux-3.10.0-862.9.1.el7/include/linux/blk_types.h
===================================================================
--- linux-3.10.0-862.9.1.el7.orig/include/linux/blk_types.h
+++ linux-3.10.0-862.9.1.el7/include/linux/blk_types.h
@@ -16,8 +16,11 @@ struct page;
 struct block_device;
 struct io_context;
 struct cgroup_subsys_state;
+struct blk_integrity_exchg;
 typedef void (bio_end_io_t) (struct bio *, int);
 typedef void (bio_destructor_t) (struct bio *);
+typedef void (integrity_gen_fn) (struct blk_integrity_exchg *bix);
+typedef int (integrity_vrfy_fn) (struct blk_integrity_exchg *bix);
 
 /*
  * was unsigned short, but we might as well be ready for > 64kB I/O pages
Index: linux-3.10.0-862.9.1.el7/include/linux/blkdev.h
===================================================================
--- linux-3.10.0-862.9.1.el7.orig/include/linux/blkdev.h
+++ linux-3.10.0-862.9.1.el7/include/linux/blkdev.h
@@ -1702,8 +1702,6 @@ struct blk_integrity_exchg {
 	const char		*disk_name;
 };
 
-typedef void (integrity_gen_fn) (struct blk_integrity_exchg *);
-typedef int (integrity_vrfy_fn) (struct blk_integrity_exchg *);
 typedef void (integrity_set_tag_fn) (void *, void *, unsigned int);
 typedef void (integrity_get_tag_fn) (void *, void *, unsigned int);