[PATCH for-next v9 6/7] block: introduce helper to map bvec iterator

[Kanchan Joshi]

Add blk_rq_map_user_bvec which maps the pages from bvec iterator into a
bio, and places the bio into the request. This helper will be used by
nvme for uring-passthrough path with pre-mapped buffers.

Signed-off-by: Kanchan Joshi <joshi.k at samsung.com>
Signed-off-by: Anuj Gupta <anuj20.g at samsung.com>
---
 block/blk-map.c        | 80 ++++++++++++++++++++++++++++++++++++++++++
 include/linux/blk-mq.h |  1 +
 2 files changed, 81 insertions(+)

diff --git a/block/blk-map.c b/block/blk-map.c
index a7838879e28e..d6265d49b15b 100644
--- a/block/blk-map.c
+++ b/block/blk-map.c
@@ -622,6 +622,86 @@ int blk_rq_map_user(struct request_queue *q, struct request *rq,
 }
 EXPORT_SYMBOL(blk_rq_map_user);
 
+/* Prepare bio for passthrough IO given an existing bvec iter */
+int blk_rq_map_user_bvec(struct request *rq, struct iov_iter *iter)
+{
+	struct request_queue *q = rq->q;
+	size_t nr_iter, nr_segs, i;
+	struct bio *bio = NULL;
+	struct bio_vec *bv, *bvecs, *bvprvp = NULL;
+	struct queue_limits *lim = &q->limits;
+	unsigned int nsegs = 0, bytes = 0;
+	bool copy = false;
+	int ret;
+	unsigned long align = q->dma_pad_mask | queue_dma_alignment(q);
+
+	/* see if we need to copy pages due to any weird situation */
+	if (blk_queue_may_bounce(q))
+		copy = true;
+	else if (iov_iter_alignment(iter) & align)
+		copy = true;
+
+	if (copy) {
+		do {
+			ret = bio_copy_user_iov(rq, NULL, iter, GFP_KERNEL);
+			if (ret) {
+				blk_rq_unmap_user(bio);
+				rq->bio = NULL;
+				break;
+			}
+			if (!bio)
+				bio = rq->bio;
+		} while (iov_iter_count(iter));
+
+		return ret;
+	}
+	/* common (non-copy) case handling */
+	nr_iter = iov_iter_count(iter);
+	nr_segs = iter->nr_segs;
+
+	if (!nr_iter || (nr_iter >> SECTOR_SHIFT) > queue_max_hw_sectors(q))
+		return -EINVAL;
+	if (nr_segs > queue_max_segments(q))
+		return -EINVAL;
+
+	/* no iovecs to alloc, as we already have a BVEC iterator */
+	bio = bio_map_get(rq, 0, GFP_KERNEL);
+	if (bio == NULL)
+		return -ENOMEM;
+
+	bio_iov_bvec_set(bio, iter);
+	blk_rq_bio_prep(rq, bio, nr_segs);
+
+	/* loop to perform a bunch of sanity checks */
+	bvecs = (struct bio_vec *)iter->bvec;
+	for (i = 0; i < nr_segs; i++) {
+		bv = &bvecs[i];
+		/*
+		 * If the queue doesn't support SG gaps and adding this
+		 * offset would create a gap, disallow it.
+		 */
+		if (bvprvp && bvec_gap_to_prev(lim, bvprvp, bv->bv_offset))
+			goto put_bio;
+
+		/* check full condition */
+		if (nsegs >= nr_segs || bytes > UINT_MAX - bv->bv_len)
+			goto put_bio;
+		if (bytes + bv->bv_len > nr_iter)
+			goto put_bio;
+		if (bv->bv_offset + bv->bv_len > PAGE_SIZE)
+			goto put_bio;
+
+		nsegs++;
+		bytes += bv->bv_len;
+		bvprvp = bv;
+	}
+	return 0;
+put_bio:
+	bio_map_put(bio);
+	return -EINVAL;
+}
+EXPORT_SYMBOL_GPL(blk_rq_map_user_bvec);
+
 /**
  * blk_rq_unmap_user - unmap a request with user data
  * @bio:	       start of bio list
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index 00a15808c137..1a9ae17e49be 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -977,6 +977,7 @@ struct rq_map_data {
 	bool from_user;
 };
 
+int blk_rq_map_user_bvec(struct request *rq, struct iov_iter *iter);
 int blk_rq_map_user(struct request_queue *, struct request *,
 		struct rq_map_data *, void __user *, unsigned long, gfp_t);
 int blk_rq_map_user_iov(struct request_queue *, struct request *,
-- 
2.25.1