block: make blk_rq_map_user take a NULL user-space buffer
This patch changes blk_rq_map_user to accept a NULL user-space buffer
with a READ command if rq_map_data is not NULL. Thus a caller can pass
page frames to lk_rq_map_user to just set up a request and bios with
page frames propely. bio_uncopy_user (called via blk_rq_unmap_user)
doesn't copy data to user space with such request.
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/include/linux/bio.h b/include/linux/bio.h
index bc386cd..7af373f 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -108,6 +108,7 @@
#define BIO_USER_MAPPED 6 /* contains user pages */
#define BIO_EOPNOTSUPP 7 /* not supported */
#define BIO_CPU_AFFINE 8 /* complete bio on same CPU as submitted */
+#define BIO_NULL_MAPPED 9 /* contains invalid user pages */
#define bio_flagged(bio, flag) ((bio)->bi_flags & (1 << (flag)))
/*