nvme-fabrics: allow discovery subsystems accept a kato

This modifies the behavior of discovery subsystems to accept
a kato as a preparation to support discovery log change
events. This also means that now every discovery controller
will have a default kato value, and for non-persistent connections
the host needs to pass in a zero kato value (keep_alive_tmo=0).
Reviewed-by: Minwoo Im <minwoo.im.dev@gmail.com>
Reviewed-by: James Smart <james.smart@broadcom.com>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Signed-off-by: Sagi Grimberg <sagi@grimberg.me>

drivers/nvme/host/fabrics.c

@@ -381,8 +381,8 @@ int nvmf_connect_admin_queue(struct nvme_ctrl *ctrl)
 	 * Set keep-alive timeout in seconds granularity (ms * 1000)
 	 * and add a grace period for controller kato enforcement
 	 */
-	cmd.connect.kato = ctrl->opts->discovery_nqn ? 0 :
-		cpu_to_le32((ctrl->kato + NVME_KATO_GRACE) * 1000);
+	cmd.connect.kato = ctrl->kato ?
+		cpu_to_le32((ctrl->kato + NVME_KATO_GRACE) * 1000) : 0;
 
 	if (ctrl->opts->disable_sqflow)
 		cmd.connect.cattr |= NVME_CONNECT_DISABLE_SQFLOW;
@@ -740,13 +740,6 @@ static int nvmf_parse_options(struct nvmf_ctrl_options *opts,
 				pr_warn("keep_alive_tmo 0 won't execute keep alives!!!\n");
 			}
 			opts->kato = token;
-
-			if (opts->discovery_nqn && opts->kato) {
-				pr_err("Discovery controllers cannot accept KATO != 0\n");
-				ret = -EINVAL;
-				goto out;
-			}
-
 			break;
 		case NVMF_OPT_CTRL_LOSS_TMO:
 			if (match_int(args, &token)) {
@@ -883,7 +876,6 @@ static int nvmf_parse_options(struct nvmf_ctrl_options *opts,
 	}
 
 	if (opts->discovery_nqn) {
-		opts->kato = 0;
 		opts->nr_io_queues = 0;
 		opts->nr_write_queues = 0;
 		opts->nr_poll_queues = 0;