fabrics: set persistent when connecting to a discovery controller

Currently a user can use the `nvme discover` to connect to a discovery
controller. This then allows the user to use a --persistent argument to
maintain a persistent or not. This correctly sets a KATO and works as
expected.

A user can also perform `nvme connect` to connect to a discovery
controller. In this case a KATO is not specified to the kernel (KATO of
0) yet we are actually creating a persistent connection. This results in
the nvme target constantly generating keep-alive timeouts as a Linux
target sets a KATO of 120 seconds (as allowed by the spec) yet we have
no keep-alive timer running for the persistent connection.

This patch checks if we are connecting to a discovery controller and if
we are sets the persistent option to true. We know it's a persistent
connection because we are using `nvme connect` so we want to stay
connected.

This fixes an issue where performing a
`nvme connect -n nqn.2014-08.org.nvmexpress.discovery ... ` to a Linux
NVMe target would result in constant keep-alive timeouts from the
target.

Signed-off-by: Alistair Francis <[email protected]>

Author: alistair23

fabrics.c

@@ -1120,6 +1120,16 @@ int nvmf_connect(const char *desc, int argc, char **argv)
 
 	nvme_parse_tls_args(keyring, tls_key, tls_key_identity, &cfg, c);
 
+	/*
+	 * We are connecting to a discovery controller, so let's treat
+	 * this as a persistent connection and specify a KATO.
+	 */
+	if (!strcmp(subsysnqn, NVME_DISC_SUBSYS_NAME)) {
+		persistent = true;
+
+		set_discovery_kato(&cfg);
+	}
+
 	ret = nvme_add_ctrl(h, c, &cfg);
 	if (ret) {
 		fprintf(stderr, "could not add new controller: %s\n",