target: Add target_alloc_session() helper function

BugLink: http://bugs.launchpad.net/bugs/1615665

Based on HCH's original patch, this adds a full version to
support percpu-ida tag pre-allocation and callback function
pointer into fabric driver code to complete session setup.
Reported-by: Christoph Hellwig <hch@lst.de>
Cc: Sagi Grimberg <sagig@mellanox.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Hannes Reinecke <hare@suse.de>
Cc: Andy Grover <agrover@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
(cherry picked from commit 7861728d)
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>

drivers/target/target_core_transport.c

@@ -281,6 +281,17 @@ struct se_session *transport_init_session_tags(unsigned int tag_num,
 	struct se_session *se_sess;
 	int rc;
 
+	if (tag_num != 0 && !tag_size) {
+		pr_err("init_session_tags called with percpu-ida tag_num:"
+		       " %u, but zero tag_size\n", tag_num);
+		return ERR_PTR(-EINVAL);
+	}
+	if (!tag_num && tag_size) {
+		pr_err("init_session_tags called with percpu-ida tag_size:"
+		       " %u, but zero tag_num\n", tag_size);
+		return ERR_PTR(-EINVAL);
+	}
+
 	se_sess = transport_init_session(sup_prot_ops);
 	if (IS_ERR(se_sess))
 		return se_sess;
@@ -375,6 +386,51 @@ void transport_register_session(
 }
 EXPORT_SYMBOL(transport_register_session);
 
+struct se_session *
+target_alloc_session(struct se_portal_group *tpg,
+		     unsigned int tag_num, unsigned int tag_size,
+		     enum target_prot_op prot_op,
+		     const char *initiatorname, void *private,
+		     int (*callback)(struct se_portal_group *,
+				     struct se_session *, void *))
+{
+	struct se_session *sess;
+
+	/*
+	 * If the fabric driver is using percpu-ida based pre allocation
+	 * of I/O descriptor tags, go ahead and perform that setup now..
+	 */
+	if (tag_num != 0)
+		sess = transport_init_session_tags(tag_num, tag_size, prot_op);
+	else
+		sess = transport_init_session(prot_op);
+
+	if (IS_ERR(sess))
+		return sess;
+
+	sess->se_node_acl = core_tpg_check_initiator_node_acl(tpg,
+					(unsigned char *)initiatorname);
+	if (!sess->se_node_acl) {
+		transport_free_session(sess);
+		return ERR_PTR(-EACCES);
+	}
+	/*
+	 * Go ahead and perform any remaining fabric setup that is
+	 * required before transport_register_session().
+	 */
+	if (callback != NULL) {
+		int rc = callback(tpg, sess, private);
+		if (rc) {
+			transport_free_session(sess);
+			return ERR_PTR(rc);
+		}
+	}
+
+	transport_register_session(tpg, sess->se_node_acl, sess, private);
+	return sess;
+}
+EXPORT_SYMBOL(target_alloc_session);
+
 static void target_release_session(struct kref *kref)
 {
 	struct se_session *se_sess = container_of(kref,

include/target/target_core_fabric.h

@@ -108,6 +108,12 @@ void target_unregister_template(const struct target_core_fabric_ops *fo);
 int target_depend_item(struct config_item *item);
 void target_undepend_item(struct config_item *item);
 
+struct se_session *target_alloc_session(struct se_portal_group *,
+		unsigned int, unsigned int, enum target_prot_op prot_op,
+		const char *, void *,
+		int (*callback)(struct se_portal_group *,
+				struct se_session *, void *));
+
 struct se_session *transport_init_session(enum target_prot_op);
 int transport_alloc_session_tags(struct se_session *, unsigned int,
 		unsigned int);