[PATCH for-next v4 3/4] block: add helper to map bvec iterator for passthrough

[Kanchan Joshi <joshi.k@xxxxxxxxxxx>]

Add blk_rq_map_user_bvec which maps the bvec iterator into a bio and
places that into the request. This helper will be used in nvme for
uring-passthrough with fixed-buffer.
While at it, create another helper bio_map_get to reduce the code
duplication.

Signed-off-by: Kanchan Joshi <joshi.k@xxxxxxxxxxx>
Signed-off-by: Anuj Gupta <anuj20.g@xxxxxxxxxxx>
---
 block/blk-map.c        | 94 +++++++++++++++++++++++++++++++++++++-----
 include/linux/blk-mq.h |  1 +
 2 files changed, 85 insertions(+), 10 deletions(-)

diff --git a/block/blk-map.c b/block/blk-map.c
index f3768876d618..e2f268167342 100644
--- a/block/blk-map.c
+++ b/block/blk-map.c
@@ -241,17 +241,10 @@ static void bio_map_put(struct bio *bio)
 	}
 }
 
-static int bio_map_user_iov(struct request *rq, struct iov_iter *iter,
+static struct bio *bio_map_get(struct request *rq, unsigned int nr_vecs,
 		gfp_t gfp_mask)
 {
-	unsigned int max_sectors = queue_max_hw_sectors(rq->q);
-	unsigned int nr_vecs = iov_iter_npages(iter, BIO_MAX_VECS);
 	struct bio *bio;
-	int ret;
-	int j;
-
-	if (!iov_iter_count(iter))
-		return -EINVAL;
 
 	if (rq->cmd_flags & REQ_POLLED) {
 		blk_opf_t opf = rq->cmd_flags | REQ_ALLOC_CACHE;
@@ -259,13 +252,31 @@ static int bio_map_user_iov(struct request *rq, struct iov_iter *iter,
 		bio = bio_alloc_bioset(NULL, nr_vecs, opf, gfp_mask,
 					&fs_bio_set);
 		if (!bio)
-			return -ENOMEM;
+			return NULL;
 	} else {
 		bio = bio_kmalloc(nr_vecs, gfp_mask);
 		if (!bio)
-			return -ENOMEM;
+			return NULL;
 		bio_init(bio, NULL, bio->bi_inline_vecs, nr_vecs, req_op(rq));
 	}
+	return bio;
+}
+
+static int bio_map_user_iov(struct request *rq, struct iov_iter *iter,
+		gfp_t gfp_mask)
+{
+	unsigned int max_sectors = queue_max_hw_sectors(rq->q);
+	unsigned int nr_vecs = iov_iter_npages(iter, BIO_MAX_VECS);
+	struct bio *bio;
+	int ret;
+	int j;
+
+	if (!iov_iter_count(iter))
+		return -EINVAL;
+
+	bio = bio_map_get(rq, nr_vecs, gfp_mask);
+	if (bio == NULL)
+		return -ENOMEM;
 
 	while (iov_iter_count(iter)) {
 		struct page **pages, *stack_pages[UIO_FASTIOV];
@@ -612,6 +623,69 @@ 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 iter_count, nr_segs;
+	struct bio *bio;
+	struct bio_vec *bv, *bvec_arr, *bvprvp = NULL;
+	struct queue_limits *lim = &q->limits;
+	unsigned int nsegs = 0, bytes = 0;
+	int ret, i;
+
+	iter_count = iov_iter_count(iter);
+	nr_segs = iter->nr_segs;
+
+	if (!iter_count || (iter_count >> 9) > 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 */
+	bvec_arr = (struct bio_vec *)iter->bvec;
+	for (i = 0; i < nr_segs; i++) {
+		bv = &bvec_arr[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)) {
+			ret = -EINVAL;
+			goto out_free;
+		}
+
+		/* check full condition */
+		if (nsegs >= nr_segs || bytes > UINT_MAX - bv->bv_len) {
+			ret = -EINVAL;
+			goto out_free;
+		}
+
+		if (bytes + bv->bv_len <= iter_count &&
+				bv->bv_offset + bv->bv_len <= PAGE_SIZE) {
+			nsegs++;
+			bytes += bv->bv_len;
+		} else {
+			ret = -EINVAL;
+			goto out_free;
+		}
+		bvprvp = bv;
+	}
+	return 0;
+out_free:
+	bio_map_put(bio);
+	return ret;
+}
+EXPORT_SYMBOL(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 b43c81d91892..83bef362f0f9 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -970,6 +970,7 @@ 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