[PATCH v3 2/2] nvmet-passthru: Cleanup nvmet_passthru_map_sg()

[Logan Gunthorpe]

Clean up some confusing elements of nvmet_passthru_map_sg() by returning
early if the request is greater than the maximum bio size. This allows
us to drop the sg_cnt variable.

This should not result in any functional change but makes the code
clearer and more understandable. The original code allocated a truncated
bio then would return EINVAL when bio_add_pc_page() filled that bio. The
new code just returns EINVAL early if this would happen.

Fixes: c1fef73f793b ("nvmet: add passthru code to process commands")
Signed-off-by: Logan Gunthorpe <logang at deltatee.com>
Suggested-by: Douglas Gilbert <dgilbert at interlog.com>
Reviewed-by: Sagi Grimberg <sagi at grimberg.me>
Cc: Christoph Hellwig <hch at lst.de>
Cc: Chaitanya Kulkarni <chaitanya.kulkarni at wdc.com>
---
 drivers/nvme/target/passthru.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/nvme/target/passthru.c b/drivers/nvme/target/passthru.c
index ed6b0586173e..0e891a286fd8 100644
--- a/drivers/nvme/target/passthru.c
+++ b/drivers/nvme/target/passthru.c
@@ -188,18 +188,20 @@ static void nvmet_passthru_req_done(struct request *rq,
 
 static int nvmet_passthru_map_sg(struct nvmet_req *req, struct request *rq)
 {
-	int sg_cnt = req->sg_cnt;
 	struct scatterlist *sg;
 	int op_flags = 0;
 	struct bio *bio;
 	int i, ret;
 
+	if (req->sg_cnt > BIO_MAX_PAGES)
+		return -EINVAL;
+
 	if (req->cmd->common.opcode == nvme_cmd_flush)
 		op_flags = REQ_FUA;
 	else if (nvme_is_write(req->cmd))
 		op_flags = REQ_SYNC | REQ_IDLE;
 
-	bio = bio_alloc(GFP_KERNEL, min(sg_cnt, BIO_MAX_PAGES));
+	bio = bio_alloc(GFP_KERNEL, req->sg_cnt);
 	bio->bi_end_io = bio_put;
 	bio->bi_opf = req_op(rq) | op_flags;
 
@@ -209,7 +211,6 @@ static int nvmet_passthru_map_sg(struct nvmet_req *req, struct request *rq)
 			bio_put(bio);
 			return -EINVAL;
 		}
-		sg_cnt--;
 	}
 
 	ret = blk_rq_append_bio(rq, &bio);
-- 
2.20.1