[PATCH 24/27] block: implement bio helper to add iter kvec pages to bio

[Jens Axboe <axboe@kernel.dk>]

For an ITER_KVEC, we can just iterate the iov and add the pages
to the bio directly.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 block/bio.c         | 30 ++++++++++++++++++++++++++++++
 include/linux/bio.h |  1 +
 2 files changed, 31 insertions(+)

diff --git a/block/bio.c b/block/bio.c
index ab174bce5436..7e59ef547ed4 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -903,6 +903,36 @@ int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
 }
 EXPORT_SYMBOL_GPL(bio_iov_iter_get_pages);
 
+/**
+ * bio_iov_kvec_add_pages - add pages from an ITER_KVEC to a bio
+ * @bio: bio to add pages to
+ * @iter: iov iterator describing the region to be added
+ *
+ * Iterate pages in the @iter and add them to the bio. We flag the
+ * @bio with BIO_HOLD_PAGES, telling IO completion not to free them.
+ */
+int bio_iov_kvec_add_pages(struct bio *bio, struct iov_iter *iter)
+{
+	unsigned short orig_vcnt = bio->bi_vcnt;
+	const struct kvec *kv;
+
+	do {
+		struct page *page;
+		size_t size;
+
+		kv = iter->kvec + iter->iov_offset;
+		page = virt_to_page(kv->iov_base);
+		size = bio_add_page(bio, page, kv->iov_len,
+					offset_in_page(kv->iov_base));
+		if (size != kv->iov_len)
+			break;
+		iov_iter_advance(iter, size);
+	} while (iov_iter_count(iter) && !bio_full(bio));
+
+	bio_set_flag(bio, BIO_HOLD_PAGES);
+	return bio->bi_vcnt > orig_vcnt ? 0 : -EINVAL;
+}
+
 static void submit_bio_wait_endio(struct bio *bio)
 {
 	complete(bio->bi_private);
diff --git a/include/linux/bio.h b/include/linux/bio.h
index 056fb627edb3..23ae8fb66b1e 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -434,6 +434,7 @@ bool __bio_try_merge_page(struct bio *bio, struct page *page,
 void __bio_add_page(struct bio *bio, struct page *page,
 		unsigned int len, unsigned int off);
 int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter);
+int bio_iov_kvec_add_pages(struct bio *bio, struct iov_iter *iter);
 struct rq_map_data;
 extern struct bio *bio_map_user_iov(struct request_queue *,
 				    struct iov_iter *, gfp_t);
-- 
2.17.1