target: Add se_sess->sess_kref + get/put helpers

This patch adds basic se_session->sess_kref and get/put helpers for fabric
session reference counting.  It sets the initial kref in transport_init_session()
and adds a target_release_session() callback to invoke TFO->close_session()
for final session shutdown.

Cc: Roland Dreier <roland@purestorage.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Joern Engel <joern@logfs.org>
Cc: Andy Grover <agrover@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/target/target_core_transport.c

@@ -246,6 +246,7 @@ struct se_session *transport_init_session(void)
 	INIT_LIST_HEAD(&se_sess->sess_cmd_list);
 	INIT_LIST_HEAD(&se_sess->sess_wait_list);
 	spin_lock_init(&se_sess->sess_cmd_lock);
+	kref_init(&se_sess->sess_kref);
 
 	return se_sess;
 }
@@ -313,6 +314,27 @@ void transport_register_session(
 }
 EXPORT_SYMBOL(transport_register_session);
 
+static void target_release_session(struct kref *kref)
+{
+	struct se_session *se_sess = container_of(kref,
+			struct se_session, sess_kref);
+	struct se_portal_group *se_tpg = se_sess->se_tpg;
+
+	se_tpg->se_tpg_tfo->close_session(se_sess);
+}
+
+void target_get_session(struct se_session *se_sess)
+{
+	kref_get(&se_sess->sess_kref);
+}
+EXPORT_SYMBOL(target_get_session);
+
+int target_put_session(struct se_session *se_sess)
+{
+	return kref_put(&se_sess->sess_kref, target_release_session);
+}
+EXPORT_SYMBOL(target_put_session);
+
 void transport_deregister_session_configfs(struct se_session *se_sess)
 {
 	struct se_node_acl *se_nacl;

include/target/target_core_base.h

@@ -654,6 +654,7 @@ struct se_session {
 	struct list_head	sess_cmd_list;
 	struct list_head	sess_wait_list;
 	spinlock_t		sess_cmd_lock;
+	struct kref		sess_kref;
 };
 
 struct se_device;

include/target/target_core_fabric.h

@@ -105,6 +105,8 @@ void	__transport_register_session(struct se_portal_group *,
 		struct se_node_acl *, struct se_session *, void *);
 void	transport_register_session(struct se_portal_group *,
 		struct se_node_acl *, struct se_session *, void *);
+void	target_get_session(struct se_session *);
+int	target_put_session(struct se_session *);
 void	transport_free_session(struct se_session *);
 void	transport_deregister_session_configfs(struct se_session *);
 void	transport_deregister_session(struct se_session *);