target: Add target_show_dynamic_sessions attribute helper

This patch adds a new helper function that can be used by fabric driver
TPG attributes for dumping the list of active sessions with a dynamically
generated se_node_acl. (generate_node_acl=1).

It prints one se_node_acl->initiatorname per line, up to PAGE_SIZE which
is due to the current limitiation of single page attribute output within
sysfs and configfs code.

Note that if a session is referencing a explicit NodeACL, the InitiatorName
will not appear within dynamic_sessions output.
Reported-by: Andy Grover <agrover@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/target/target_core_transport.c

@@ -404,6 +404,30 @@ void target_put_session(struct se_session *se_sess)
 }
 EXPORT_SYMBOL(target_put_session);
 
+ssize_t target_show_dynamic_sessions(struct se_portal_group *se_tpg, char *page)
+{
+	struct se_session *se_sess;
+	ssize_t len = 0;
+
+	spin_lock_bh(&se_tpg->session_lock);
+	list_for_each_entry(se_sess, &se_tpg->tpg_sess_list, sess_list) {
+		if (!se_sess->se_node_acl)
+			continue;
+		if (!se_sess->se_node_acl->dynamic_node_acl)
+			continue;
+		if (strlen(se_sess->se_node_acl->initiatorname) + 1 + len > PAGE_SIZE)
+			break;
+
+		len += snprintf(page + len, PAGE_SIZE - len, "%s\n",
+				se_sess->se_node_acl->initiatorname);
+		len += 1; /* Include NULL terminator */
+	}
+	spin_unlock_bh(&se_tpg->session_lock);
+
+	return len;
+}
+EXPORT_SYMBOL(target_show_dynamic_sessions);
+
 static void target_complete_nacl(struct kref *kref)
 {
 	struct se_node_acl *nacl = container_of(kref,

include/target/target_core_fabric.h

@@ -95,6 +95,7 @@ void	transport_register_session(struct se_portal_group *,
 		struct se_node_acl *, struct se_session *, void *);
 void	target_get_session(struct se_session *);
 void	target_put_session(struct se_session *);
+ssize_t	target_show_dynamic_sessions(struct se_portal_group *, char *);
 void	transport_free_session(struct se_session *);
 void	target_put_nacl(struct se_node_acl *);
 void	transport_deregister_session_configfs(struct se_session *);

include/target/target_core_fabric_configfs.h

@@ -90,6 +90,11 @@ static struct target_fabric_tpg_attribute _fabric##_tpg_##_name =	\
 	_fabric##_tpg_store_##_name);
 
 
+#define TF_TPG_BASE_ATTR_RO(_fabric, _name)				\
+static struct target_fabric_tpg_attribute _fabric##_tpg_##_name =	\
+	__CONFIGFS_EATTR_RO(_name,					\
+	_fabric##_tpg_show_##_name);
+
 CONFIGFS_EATTR_STRUCT(target_fabric_wwn, target_fabric_configfs);
 #define TF_WWN_ATTR(_fabric, _name, _mode)				\
 static struct target_fabric_wwn_attribute _fabric##_wwn_##_name =	\