target_submit_cmd_map_sgls is being removed, so convert xen
to the new submission API. This has it use
target_init_cmd/target_submit_prep/target_submit because we need to
have lio core map sgls which is now done in target_submit_prep.
target_init_cmd will never fail for xen because it does it's
own sync during session shutdown, so we can remove that code.

Note: xen never calls target_stop_session so
target_submit_cmd_map_sgls never failed (in the new API
target_init_cmd handles target_stop_session being called when cmds
are being submitted). If it were to have used target_stop_session
and got an error, we would have hit a refcount bug like xen and usb,
because it does:

    if (rc < 0) {
            transport_send_check_condition_and_sense(se_cmd,
                            TCM_LOGICAL_UNIT_COMMUNICATION_FAILURE, 0);
            transport_generic_free_cmd(se_cmd, 0);
    }

transport_send_check_condition_and_sense calls queue_status which
calls scsiback_cmd_done->target_put_sess_cmd. We do an extra
transport_generic_free_cmd call above which would have dropped
the refcount to -1 and the refcount code would spit out errors.

Signed-off-by: Mike Christie <michael.christie@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
---
 drivers/xen/xen-scsiback.c | 21 +++++++++------------
 1 file changed, 9 insertions(+), 12 deletions(-)

diff --git a/drivers/xen/xen-scsiback.c b/drivers/xen/xen-scsiback.c
index 862162dca33c..7bf9a6bede6d 100644
--- a/drivers/xen/xen-scsiback.c
+++ b/drivers/xen/xen-scsiback.c

@@ -360,21 +360,18 @@ static void scsiback_cmd_exec(struct vscsibk_pend *pending_req)
 {
 	struct se_cmd *se_cmd = &pending_req->se_cmd;
 	struct se_session *sess = pending_req->v2p->tpg->tpg_nexus->tvn_se_sess;
-	int rc;
 
 	scsiback_get(pending_req->info);
 	se_cmd->tag = pending_req->rqid;
-	rc = target_submit_cmd_map_sgls(se_cmd, sess, pending_req->cmnd,
-			pending_req->sense_buffer, pending_req->v2p->lun,
-			pending_req->data_len, 0,
-			pending_req->sc_data_direction, TARGET_SCF_ACK_KREF,
-			pending_req->sgl, pending_req->n_sg,
-			NULL, 0, NULL, 0);
-	if (rc < 0) {
-		transport_send_check_condition_and_sense(se_cmd,
-				TCM_LOGICAL_UNIT_COMMUNICATION_FAILURE, 0);
-		transport_generic_free_cmd(se_cmd, 0);
-	}
+	target_init_cmd(se_cmd, sess, pending_req->sense_buffer,
+			pending_req->v2p->lun, pending_req->data_len, 0,
+			pending_req->sc_data_direction, TARGET_SCF_ACK_KREF);
+
+	if (target_submit_prep(se_cmd, pending_req->cmnd, pending_req->sgl,
+			       pending_req->n_sg, NULL, 0, NULL, 0))
+		return;
+
+	target_submit(se_cmd);
 }
 
 static int scsiback_gnttab_data_map_batch(struct gnttab_map_grant_ref *map,

-- 
2.25.1