Add BLK_EXPECTED_REF_TAG_CAPABLE to enum blk_integrity_flags to allow a
device to report support for specifying an expected initial ref tag in
I/O. Make blk_integrity_remap() a no-op if the flag is set, as the ref
tag seed used to generate/verify ref tags in the protection information
can be passed as the expected initial ref tag.

Ref tag remapping is necessary to merge bios with non-contiguous ref tag
seeds, as it converts both bios' ref tags to/from absolute integrity
interval numbers, which are contiguous. So don't merge bios to a
BLK_EXPECTED_REF_TAG_CAPABLE device if the next bio's ref tag seed
doesn't match the ref tag that would follow the end of the first bio.

Signed-off-by: Caleb Sander Mateos <csander@purestorage.com>
---
 block/blk-integrity.c         | 18 ++++++++++++++++++
 block/t10-pi.c                |  3 ++-
 include/linux/blk-integrity.h |  2 ++
 3 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/block/blk-integrity.c b/block/blk-integrity.c
index 964eebbee14d..85ebe13f0912 100644
--- a/block/blk-integrity.c
+++ b/block/blk-integrity.c
@@ -139,10 +139,12 @@ EXPORT_SYMBOL_GPL(blk_rq_integrity_map_user);
 
 bool blk_integrity_merge_rq(struct request_queue *q, struct request *req,
 			    struct request *next)
 {
 	struct bio_integrity_payload *bip, *bip_next;
+	struct blk_integrity *bi;
+	u64 intervals;
 
 	if (blk_integrity_rq(req) == 0 && blk_integrity_rq(next) == 0)
 		return true;
 
 	if (blk_integrity_rq(req) == 0 || blk_integrity_rq(next) == 0)
@@ -155,10 +157,17 @@ bool blk_integrity_merge_rq(struct request_queue *q, struct request *req,
 
 	if (bip->bip_flags & BIP_CHECK_APPTAG &&
 	    bip->app_tag != bip_next->app_tag)
 		return false;
 
+	bi = blk_get_integrity(req->bio->bi_bdev->bd_disk);
+	intervals = blk_rq_bytes(req) >> bi->interval_exp;
+	if (bip->bip_flags & BIP_CHECK_REFTAG &&
+	    bi->flags & BLK_EXPECTED_REF_TAG_CAPABLE &&
+	    bip->bip_iter.bi_sector + intervals != bip_next->bip_iter.bi_sector)
+		return false;
+
 	if (req->nr_integrity_segments + next->nr_integrity_segments >
 	    q->limits.max_integrity_segments)
 		return false;
 
 	if (integrity_req_gap_back_merge(req, next->bio))
@@ -169,11 +178,13 @@ bool blk_integrity_merge_rq(struct request_queue *q, struct request *req,
 
 bool blk_integrity_merge_bio(struct request_queue *q, struct request *req,
 			     struct bio *bio)
 {
 	struct bio_integrity_payload *bip, *bip_bio = bio_integrity(bio);
+	struct blk_integrity *bi;
 	int nr_integrity_segs;
+	u64 intervals;
 
 	if (blk_integrity_rq(req) == 0 && bip_bio == NULL)
 		return true;
 
 	if (blk_integrity_rq(req) == 0 || bip_bio == NULL)
@@ -185,10 +196,17 @@ bool blk_integrity_merge_bio(struct request_queue *q, struct request *req,
 
 	if (bip->bip_flags & BIP_CHECK_APPTAG &&
 	    bip->app_tag != bip_bio->app_tag)
 		return false;
 
+	bi = blk_get_integrity(req->bio->bi_bdev->bd_disk);
+	intervals = blk_rq_bytes(req) >> bi->interval_exp;
+	if (bip->bip_flags & BIP_CHECK_REFTAG &&
+	    bi->flags & BLK_EXPECTED_REF_TAG_CAPABLE &&
+	    bip->bip_iter.bi_sector + intervals != bip_bio->bip_iter.bi_sector)
+		return false;
+
 	nr_integrity_segs = blk_rq_count_integrity_sg(q, bio);
 	if (req->nr_integrity_segments + nr_integrity_segs >
 	    q->limits.max_integrity_segments)
 		return false;
 
diff --git a/block/t10-pi.c b/block/t10-pi.c
index 71367fd082bd..becf3e316b06 100644
--- a/block/t10-pi.c
+++ b/block/t10-pi.c
@@ -545,11 +545,12 @@ static void blk_integrity_remap(struct request *rq, unsigned int nr_bytes,
 	struct blk_integrity *bi = &rq->q->limits.integrity;
 	u64 ref = bio_integrity_intervals(bi, blk_rq_pos(rq));
 	unsigned intervals = nr_bytes >> bi->interval_exp;
 	struct bio *bio;
 
-	if (!(bi->flags & BLK_INTEGRITY_REF_TAG))
+	if (!(bi->flags & BLK_INTEGRITY_REF_TAG) ||
+	    bi->flags & BLK_EXPECTED_REF_TAG_CAPABLE)
 		return;
 
 	__rq_for_each_bio(bio, rq) {
 		__blk_reftag_remap(bio, bi, &intervals, &ref, prep);
 		if (!intervals)
diff --git a/include/linux/blk-integrity.h b/include/linux/blk-integrity.h
index c82b2f6fe194..e314d22d9922 100644
--- a/include/linux/blk-integrity.h
+++ b/include/linux/blk-integrity.h
@@ -13,10 +13,12 @@ enum blk_integrity_flags {
 	BLK_INTEGRITY_NOGENERATE	= 1 << 1,
 	BLK_INTEGRITY_DEVICE_CAPABLE	= 1 << 2,
 	BLK_INTEGRITY_REF_TAG		= 1 << 3,
 	BLK_INTEGRITY_STACKED		= 1 << 4,
 	BLK_SPLIT_INTERVAL_CAPABLE	= 1 << 5,
+	/* Device I/O specifies expected initial ref tag independent of LBA */
+	BLK_EXPECTED_REF_TAG_CAPABLE	= 1 << 6,
 };
 
 const char *blk_integrity_profile_name(struct blk_integrity *bi);
 bool queue_limits_stack_integrity(struct queue_limits *t,
 		struct queue_limits *b);
-- 
2.54.0