[PATCH for-next v10 6/7] block: extend functionality to map bvec iterator

[Kanchan Joshi <joshi.k@xxxxxxxxxxx>]

Extend blk_rq_map_user_iov so that it can handle bvec iterator.
It  maps the pages from bvec iterator into a bio and place the bio into
request.

This helper will be used by nvme for uring-passthrough path when IO is
done using pre-mapped buffers.

Signed-off-by: Kanchan Joshi <joshi.k@xxxxxxxxxxx>
Signed-off-by: Anuj Gupta <anuj20.g@xxxxxxxxxxx>
---
 block/blk-map.c | 77 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 77 insertions(+)

diff --git a/block/blk-map.c b/block/blk-map.c
index a7838879e28e..a1aa8dacb02b 100644
--- a/block/blk-map.c
+++ b/block/blk-map.c
@@ -548,6 +548,74 @@ int blk_rq_append_bio(struct request *rq, struct bio *bio)
 }
 EXPORT_SYMBOL(blk_rq_append_bio);
 
+/* Prepare bio for passthrough IO given ITER_BVEC iter */
+static int blk_rq_map_user_bvec(struct request *rq, const struct iov_iter *iter,
+				bool *copy)
+{
+	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;
+	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))
+		goto out_copy;
+	else if (iov_iter_alignment(iter) & align)
+		goto out_copy;
+	/* virt-alignment gap is checked anyway down, so avoid extra loop here */
+
+	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, (struct iov_iter *)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, fallback to copy.
+		 */
+		if (bvprvp && bvec_gap_to_prev(lim, bvprvp, bv->bv_offset)) {
+			bio_map_put(bio);
+			goto out_copy;
+		}
+		/* 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;
+out_copy:
+	*copy = true;
+	return 0;
+}
+
 /**
  * blk_rq_map_user_iov - map user data to a request, for passthrough requests
  * @q:		request queue where request should be inserted
@@ -573,6 +641,14 @@ int blk_rq_map_user_iov(struct request_queue *q, struct request *rq,
 	struct iov_iter i;
 	int ret = -EINVAL;
 
+	if (iov_iter_is_bvec(iter)) {
+		ret = blk_rq_map_user_bvec(rq, iter, &copy);
+		if (ret != 0)
+			goto fail;
+		if (copy)
+			goto do_copy;
+		return ret;
+	}
 	if (!iter_is_iovec(iter))
 		goto fail;
 
@@ -585,6 +661,7 @@ int blk_rq_map_user_iov(struct request_queue *q, struct request *rq,
 	else if (queue_virt_boundary(q))
 		copy = queue_virt_boundary(q) & iov_iter_gap_alignment(iter);
 
+do_copy:
 	i = *iter;
 	do {
 		if (copy)
-- 
2.25.1