nvme: factor out a add nvme_is_write helper

BugLink: https://bugs.launchpad.net/bugs/1664602

Centralize the check if a given NVMe command reads or writes data.
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Jay Freyensee <james.p.freyensee@intel.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
(backported from commit 7a5abb4b)
Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
Acked-By: AceLan Kao <acelan.kao@canonical.com>
Acked-By: Shrirang Bagul <shrirang.bagul@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

drivers/nvme/host/core.c

@@ -92,10 +92,9 @@ void nvme_requeue_req(struct request *req)
 struct request *nvme_alloc_request(struct request_queue *q,
 		struct nvme_command *cmd, unsigned int flags)
 {
-	bool write = cmd->common.opcode & 1;
 	struct request *req;
 
-	req = blk_mq_alloc_request(q, write, flags);
+	req = blk_mq_alloc_request(q, nvme_is_write(cmd), flags);
 	if (IS_ERR(req))
 		return req;
 
@@ -153,7 +152,7 @@ int __nvme_submit_user_cmd(struct request_queue *q, struct nvme_command *cmd,
 		void __user *meta_buffer, unsigned meta_len, u32 meta_seed,
 		u32 *result, unsigned timeout)
 {
-	bool write = cmd->common.opcode & 1;
+	bool write = nvme_is_write(cmd);
 	struct nvme_completion cqe;
 	struct nvme_ns *ns = q->queuedata;
 	struct gendisk *disk = ns ? ns->disk : NULL;