nvmet: implement valid sqhd values in completions

To support sqhd, for initiators that are following the spec and
paying attention to sqhd vs their sqtail values:

- add sqhd to struct nvmet_sq
- initialize sqhd to 0 in nvmet_sq_setup
- rather than propagate the 0's-based qsize value from the connect message
  which requires a +1 in every sqhd update, and as nothing else references
  it, convert to 1's-based value in nvmt_sq/cq_setup() calls.
- validate connect message sqsize being non-zero per spec.
- updated assign sqhd for every completion that goes back.

Also remove handling the NULL sq case in __nvmet_req_complete, as it can't
happen with the current code.
Signed-off-by: NJames Smart <james.smart@broadcom.com>
Reviewed-by: NSagi Grimberg <sagi@grimberg.me>
Reviewed-by: NMax Gurtovoy <maxg@mellanox.com>
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

drivers/nvme/target/core.c

@@ -390,9 +390,8 @@ static void __nvmet_req_complete(struct nvmet_req *req, u16 status)
 	if (status)
 		nvmet_set_status(req, status);
 
-	/* XXX: need to fill in something useful for sq_head */
-	req->rsp->sq_head = 0;
-	if (likely(req->sq)) /* may happen during early failure */
+	req->sq->sqhd = (req->sq->sqhd + 1) % req->sq->size;
+	req->rsp->sq_head = cpu_to_le16(req->sq->sqhd);
 	req->rsp->sq_id = cpu_to_le16(req->sq->qid);
 	req->rsp->command_id = req->cmd->common.command_id;
 
@@ -420,6 +419,7 @@ void nvmet_cq_setup(struct nvmet_ctrl *ctrl, struct nvmet_cq *cq,
 void nvmet_sq_setup(struct nvmet_ctrl *ctrl, struct nvmet_sq *sq,
 		u16 qid, u16 size)
 {
+	sq->sqhd = 0;
 	sq->qid = qid;
 	sq->size = size;
 

drivers/nvme/target/fabrics-cmd.c

@@ -109,9 +109,14 @@ static u16 nvmet_install_queue(struct nvmet_ctrl *ctrl, struct nvmet_req *req)
 		pr_warn("queue already connected!\n");
 		return NVME_SC_CONNECT_CTRL_BUSY | NVME_SC_DNR;
 	}
+	if (!sqsize) {
+		pr_warn("queue size zero!\n");
+		return NVME_SC_CONNECT_INVALID_PARAM | NVME_SC_DNR;
+	}
 
-	nvmet_cq_setup(ctrl, req->cq, qid, sqsize);
-	nvmet_sq_setup(ctrl, req->sq, qid, sqsize);
+	/* note: convert queue size from 0's-based value to 1's-based value */
+	nvmet_cq_setup(ctrl, req->cq, qid, sqsize + 1);
+	nvmet_sq_setup(ctrl, req->sq, qid, sqsize + 1);
 	return 0;
 }
 

drivers/nvme/target/nvmet.h

@@ -74,6 +74,7 @@ struct nvmet_sq {
 	struct percpu_ref	ref;
 	u16			qid;
 	u16			size;
+	u16			sqhd;
 	struct completion	free_done;
 	struct completion	confirm_done;
 };