[PATCH 02/19] block: add a bdev_rw_virt helper

[Christoph Hellwig <hch@lst.de>]

Add a helper to perform synchronous I/O on a kernel direct map range.
Currently this is implemented in various places in usually not very
efficient ways, so provide a generic helper instead.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
---
 block/bio.c         | 30 ++++++++++++++++++++++++++++++
 include/linux/bio.h |  5 ++++-
 2 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/block/bio.c b/block/bio.c
index c1789a58f23f..8db2db0bba0f 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -1317,6 +1317,36 @@ int submit_bio_wait(struct bio *bio)
 }
 EXPORT_SYMBOL(submit_bio_wait);
 
+/**
+ * bdev_rw_virt - synchronously read into / write from kernel mapping
+ * @bdev:	block device to access
+ * @sector:	sector to access
+ * @data:	data to read/write
+ * @len:	length in byte to read/write
+ * @op:		operation (e.g. REQ_OP_READ/REQ_OP_WRITE)
+ *
+ * Performs synchronous I/O to @bdev for @data/@len.  @data must be in
+ * the kernel direct mapping and not a vmalloc address.
+ */
+int bdev_rw_virt(struct block_device *bdev, sector_t sector, void *data,
+		size_t len, enum req_op op)
+{
+	struct bio_vec bv;
+	struct bio bio;
+	int error;
+
+	if (WARN_ON_ONCE(is_vmalloc_addr(data)))
+		return -EIO;
+
+	bio_init(&bio, bdev, &bv, 1, op);
+	bio.bi_iter.bi_sector = sector;
+	bio_add_virt_nofail(&bio, data, len);
+	error = submit_bio_wait(&bio);
+	bio_uninit(&bio);
+	return error;
+}
+EXPORT_SYMBOL_GPL(bdev_rw_virt);
+
 static void bio_wait_end_io(struct bio *bio)
 {
 	complete(bio->bi_private);
diff --git a/include/linux/bio.h b/include/linux/bio.h
index acca7464080c..ad54e6af20dc 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -402,7 +402,6 @@ static inline int bio_iov_vecs_to_alloc(struct iov_iter *iter, int max_segs)
 
 struct request_queue;
 
-extern int submit_bio_wait(struct bio *bio);
 void bio_init(struct bio *bio, struct block_device *bdev, struct bio_vec *table,
 	      unsigned short max_vecs, blk_opf_t opf);
 extern void bio_uninit(struct bio *);
@@ -419,6 +418,10 @@ void bio_add_folio_nofail(struct bio *bio, struct folio *folio, size_t len,
 			  size_t off);
 void bio_add_virt_nofail(struct bio *bio, void *vaddr, unsigned len);
 
+int submit_bio_wait(struct bio *bio);
+int bdev_rw_virt(struct block_device *bdev, sector_t sector, void *data,
+		size_t len, enum req_op op);
+
 int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter);
 void bio_iov_bvec_set(struct bio *bio, const struct iov_iter *iter);
 void __bio_release_pages(struct bio *bio, bool mark_dirty);
-- 
2.47.2