[SCSI] block: make blk_rq_map_user take a NULL user-space buffer for WRITE

The commit 818827669d85b84241696ffef2de485db46b0b5e (block: make
blk_rq_map_user take a NULL user-space buffer) extended
blk_rq_map_user to accept a NULL user-space buffer with a READ
command. It was necessary to convert sg to use the block layer mapping
API.

This patch extends blk_rq_map_user again for a WRITE command. It is
necessary to convert st and osst drivers to use the block layer
apping API.

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Acked-by: Jens Axboe <jens.axboe@oracle.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>

block/blk-map.c

@@ -42,7 +42,7 @@ static int __blk_rq_unmap_user(struct bio *bio)
 
 static int __blk_rq_map_user(struct request_queue *q, struct request *rq,
 			     struct rq_map_data *map_data, void __user *ubuf,
-			     unsigned int len, int null_mapped, gfp_t gfp_mask)
+			     unsigned int len, gfp_t gfp_mask)
 {
 	unsigned long uaddr;
 	struct bio *bio, *orig_bio;
@@ -63,7 +63,7 @@ static int __blk_rq_map_user(struct request_queue *q, struct request *rq,
 	if (IS_ERR(bio))
 		return PTR_ERR(bio);
 
-	if (null_mapped)
+	if (map_data && map_data->null_mapped)
 		bio->bi_flags |= (1 << BIO_NULL_MAPPED);
 
 	orig_bio = bio;
@@ -114,17 +114,15 @@ int blk_rq_map_user(struct request_queue *q, struct request *rq,
 {
 	unsigned long bytes_read = 0;
 	struct bio *bio = NULL;
-	int ret, null_mapped = 0;
+	int ret;
 
 	if (len > (q->max_hw_sectors << 9))
 		return -EINVAL;
 	if (!len)
 		return -EINVAL;
-	if (!ubuf) {
-		if (!map_data || rq_data_dir(rq) != READ)
-			return -EINVAL;
-		null_mapped = 1;
-	}
+
+	if (!ubuf && (!map_data || !map_data->null_mapped))
+		return -EINVAL;
 
 	while (bytes_read != len) {
 		unsigned long map_len, end, start;
@@ -143,7 +141,7 @@ int blk_rq_map_user(struct request_queue *q, struct request *rq,
 			map_len -= PAGE_SIZE;
 
 		ret = __blk_rq_map_user(q, rq, map_data, ubuf, map_len,
-					null_mapped, gfp_mask);
+					gfp_mask);
 		if (ret < 0)
 			goto unmap_rq;
 		if (!bio)

drivers/scsi/sg.c

@@ -1670,6 +1670,7 @@ static int sg_start_req(Sg_request *srp, unsigned char *cmd)
 		md->page_order = req_schp->page_order;
 		md->nr_entries = req_schp->k_use_sg;
 		md->offset = 0;
+		md->null_mapped = hp->dxferp ? 0 : 1;
 	}
 
 	if (iov_count)

fs/bio.c

@@ -859,7 +859,7 @@ struct bio *bio_copy_user_iov(struct request_queue *q,
 	/*
 	 * success
 	 */
-	if (!write_to_vm) {
+	if (!write_to_vm && (!map_data || !map_data->null_mapped)) {
 		ret = __bio_copy_iov(bio, bio->bi_io_vec, iov, iov_count, 0, 0);
 		if (ret)
 			goto cleanup;

include/linux/blkdev.h

@@ -691,6 +691,7 @@ struct rq_map_data {
 	int page_order;
 	int nr_entries;
 	unsigned long offset;
+	int null_mapped;
 };
 
 struct req_iterator {