target: simplify backend driver registration

Rewrite the backend driver registration based on what we did to the fabric
drivers:  introduce a read-only struct target_bakckend_ops that the driver
registers, which is then instanciate as a struct target_backend by the
core.  This allows the ops vector to be smaller and allows us to mark it
const.  At the same time the registration function can set up the
configfs attributes, avoiding the need to add additional boilerplate code
for that to the drivers.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

11 files changed, 135 insertions, 158 deletions

diff --git a/drivers/target/target_core_configfs.c b/drivers/target/target_core_configfs.c
index 4a31d4765390..57c099dd9da5 100644
--- a/drivers/target/target_core_configfs.c
+++ b/drivers/target/target_core_configfs.c
@@ -51,15 +51,26 @@
 #include "target_core_xcopy.h"
 
 #define TB_CIT_SETUP(_name, _item_ops, _group_ops, _attrs)		\
-static void target_core_setup_##_name##_cit(struct se_subsystem_api *sa) \
+static void target_core_setup_##_name##_cit(struct target_backend *tb)	\
 {									\
-	struct target_backend_cits *tbc = &sa->tb_cits;			\
-	struct config_item_type *cit = &tbc->tb_##_name##_cit;		\
+	struct config_item_type *cit = &tb->tb_##_name##_cit;		\
 									\
 	cit->ct_item_ops = _item_ops;					\
 	cit->ct_group_ops = _group_ops;					\
 	cit->ct_attrs = _attrs;						\
-	cit->ct_owner = sa->owner;					\
+	cit->ct_owner = tb->ops->owner;					\
+	pr_debug("Setup generic %s\n", __stringify(_name));		\
+}
+
+#define TB_CIT_SETUP_DRV(_name, _item_ops, _group_ops)			\
+static void target_core_setup_##_name##_cit(struct target_backend *tb)	\
+{									\
+	struct config_item_type *cit = &tb->tb_##_name##_cit;		\
+									\
+	cit->ct_item_ops = _item_ops;					\
+	cit->ct_group_ops = _group_ops;					\
+	cit->ct_attrs = tb->ops->tb_##_name##_attrs;			\
+	cit->ct_owner = tb->ops->owner;					\
 	pr_debug("Setup generic %s\n", __stringify(_name));		\
 }
 
@@ -469,7 +480,7 @@ static struct configfs_item_operations target_core_dev_attrib_ops = {
 	.store_attribute	= target_core_dev_attrib_attr_store,
 };
 
-TB_CIT_SETUP(dev_attrib, &target_core_dev_attrib_ops, NULL, NULL);
+TB_CIT_SETUP_DRV(dev_attrib, &target_core_dev_attrib_ops, NULL);
 
 /* End functions for struct config_item_type tb_dev_attrib_cit */
 
@@ -1174,13 +1185,13 @@ TB_CIT_SETUP(dev_pr, &target_core_dev_pr_ops, NULL, target_core_dev_pr_attrs);
 static ssize_t target_core_show_dev_info(void *p, char *page)
 {
 	struct se_device *dev = p;
-	struct se_subsystem_api *t = dev->transport;
 	int bl = 0;
 	ssize_t read_bytes = 0;
 
 	transport_dump_dev_state(dev, page, &bl);
 	read_bytes += bl;
-	read_bytes += t->show_configfs_dev_params(dev, page+read_bytes);
+	read_bytes += dev->transport->show_configfs_dev_params(dev,
+			page+read_bytes);
 	return read_bytes;
 }
 
@@ -1198,9 +1209,8 @@ static ssize_t target_core_store_dev_control(
 	size_t count)
 {
 	struct se_device *dev = p;
-	struct se_subsystem_api *t = dev->transport;
 
-	return t->set_configfs_dev_params(dev, page, count);
+	return dev->transport->set_configfs_dev_params(dev, page, count);
 }
 
 static struct target_core_configfs_attribute target_core_attr_dev_control = {
@@ -2477,9 +2487,9 @@ static struct config_group *target_core_make_subdev(
 	const char *name)
 {
 	struct t10_alua_tg_pt_gp *tg_pt_gp;
-	struct se_subsystem_api *t;
 	struct config_item *hba_ci = &group->cg_item;
 	struct se_hba *hba = item_to_hba(hba_ci);
+	struct target_backend *tb = hba->backend;
 	struct se_device *dev;
 	struct config_group *dev_cg = NULL, *tg_pt_gp_cg = NULL;
 	struct config_group *dev_stat_grp = NULL;
@@ -2488,10 +2498,6 @@ static struct config_group *target_core_make_subdev(
 	ret = mutex_lock_interruptible(&hba->hba_access_mutex);
 	if (ret)
 		return ERR_PTR(ret);
-	/*
-	 * Locate the struct se_subsystem_api from parent's struct se_hba.
-	 */
-	t = hba->transport;
 
 	dev = target_alloc_device(hba, name);
 	if (!dev)
@@ -2504,17 +2510,17 @@ static struct config_group *target_core_make_subdev(
 	if (!dev_cg->default_groups)
 		goto out_free_device;
 
-	config_group_init_type_name(dev_cg, name, &t->tb_cits.tb_dev_cit);
+	config_group_init_type_name(dev_cg, name, &tb->tb_dev_cit);
 	config_group_init_type_name(&dev->dev_attrib.da_group, "attrib",
-			&t->tb_cits.tb_dev_attrib_cit);
+			&tb->tb_dev_attrib_cit);
 	config_group_init_type_name(&dev->dev_pr_group, "pr",
-			&t->tb_cits.tb_dev_pr_cit);
+			&tb->tb_dev_pr_cit);
 	config_group_init_type_name(&dev->t10_wwn.t10_wwn_group, "wwn",
-			&t->tb_cits.tb_dev_wwn_cit);
+			&tb->tb_dev_wwn_cit);
 	config_group_init_type_name(&dev->t10_alua.alua_tg_pt_gps_group,
-			"alua", &t->tb_cits.tb_dev_alua_tg_pt_gps_cit);
+			"alua", &tb->tb_dev_alua_tg_pt_gps_cit);
 	config_group_init_type_name(&dev->dev_stat_grps.stat_group,
-			"statistics", &t->tb_cits.tb_dev_stat_cit);
+			"statistics", &tb->tb_dev_stat_cit);
 
 	dev_cg->default_groups[0] = &dev->dev_attrib.da_group;
 	dev_cg->default_groups[1] = &dev->dev_pr_group;
@@ -2644,7 +2650,7 @@ static ssize_t target_core_hba_show_attr_hba_info(
 	char *page)
 {
 	return sprintf(page, "HBA Index: %d plugin: %s version: %s\n",
-			hba->hba_id, hba->transport->name,
+			hba->hba_id, hba->backend->ops->name,
 			TARGET_CORE_CONFIGFS_VERSION);
 }
 
@@ -2664,11 +2670,10 @@ static ssize_t target_core_hba_show_attr_hba_mode(struct se_hba *hba,
 static ssize_t target_core_hba_store_attr_hba_mode(struct se_hba *hba,
 				const char *page, size_t count)
 {
-	struct se_subsystem_api *transport = hba->transport;
 	unsigned long mode_flag;
 	int ret;
 
-	if (transport->pmode_enable_hba == NULL)
+	if (hba->backend->ops->pmode_enable_hba == NULL)
 		return -EINVAL;
 
 	ret = kstrtoul(page, 0, &mode_flag);
@@ -2682,7 +2687,7 @@ static ssize_t target_core_hba_store_attr_hba_mode(struct se_hba *hba,
 		return -EINVAL;
 	}
 
-	ret = transport->pmode_enable_hba(hba, mode_flag);
+	ret = hba->backend->ops->pmode_enable_hba(hba, mode_flag);
 	if (ret < 0)
 		return -EINVAL;
 	if (ret > 0)
@@ -2808,16 +2813,15 @@ static struct config_item_type target_core_cit = {
 
 /* Stop functions for struct config_item_type target_core_hba_cit */
 
-void target_core_setup_sub_cits(struct se_subsystem_api *sa)
+void target_setup_backend_cits(struct target_backend *tb)
 {
-	target_core_setup_dev_cit(sa);
-	target_core_setup_dev_attrib_cit(sa);
-	target_core_setup_dev_pr_cit(sa);
-	target_core_setup_dev_wwn_cit(sa);
-	target_core_setup_dev_alua_tg_pt_gps_cit(sa);
-	target_core_setup_dev_stat_cit(sa);
+	target_core_setup_dev_cit(tb);
+	target_core_setup_dev_attrib_cit(tb);
+	target_core_setup_dev_pr_cit(tb);
+	target_core_setup_dev_wwn_cit(tb);
+	target_core_setup_dev_alua_tg_pt_gps_cit(tb);
+	target_core_setup_dev_stat_cit(tb);
 }
-EXPORT_SYMBOL(target_core_setup_sub_cits);
 
 static int __init target_core_init_configfs(void)
 {
diff --git a/drivers/target/target_core_device.c b/drivers/target/target_core_device.c
index 47a73609e277..af906f1caaa7 100644
--- a/drivers/target/target_core_device.c
+++ b/drivers/target/target_core_device.c
@@ -1367,13 +1367,13 @@ struct se_device *target_alloc_device(struct se_hba *hba, const char *name)
 	struct se_device *dev;
 	struct se_lun *xcopy_lun;
 
-	dev = hba->transport->alloc_device(hba, name);
+	dev = hba->backend->ops->alloc_device(hba, name);
 	if (!dev)
 		return NULL;
 
 	dev->dev_link_magic = SE_DEV_LINK_MAGIC;
 	dev->se_hba = hba;
-	dev->transport = hba->transport;
+	dev->transport = hba->backend->ops;
 	dev->prot_length = sizeof(struct se_dif_v1_tuple);
 
 	INIT_LIST_HEAD(&dev->dev_list);
@@ -1571,7 +1571,7 @@ int core_dev_setup_virtual_lun0(void)
 		goto out_free_hba;
 	}
 
-	hba->transport->set_configfs_dev_params(dev, buf, sizeof(buf));
+	hba->backend->ops->set_configfs_dev_params(dev, buf, sizeof(buf));
 
 	ret = target_configure_device(dev);
 	if (ret)
diff --git a/drivers/target/target_core_file.c b/drivers/target/target_core_file.c
index e865885352da..7c5b1ef57d34 100644
--- a/drivers/target/target_core_file.c
+++ b/drivers/target/target_core_file.c
@@ -46,10 +46,6 @@ static inline struct fd_dev *FD_DEV(struct se_device *dev)
 	return container_of(dev, struct fd_dev, dev);
 }
 
-/*	fd_attach_hba(): (Part of se_subsystem_api_t template)
- *
- *
- */
 static int fd_attach_hba(struct se_hba *hba, u32 host_id)
 {
 	struct fd_host *fd_host;
@@ -881,7 +877,7 @@ static struct configfs_attribute *fileio_backend_dev_attrs[] = {
 	NULL,
 };
 
-static struct se_subsystem_api fileio_template = {
+static const struct target_backend_ops fileio_ops = {
 	.name			= "fileio",
 	.inquiry_prod		= "FILEIO",
 	.inquiry_rev		= FD_VERSION,
@@ -899,21 +895,17 @@ static struct se_subsystem_api fileio_template = {
 	.init_prot		= fd_init_prot,
 	.format_prot		= fd_format_prot,
 	.free_prot		= fd_free_prot,
+	.tb_dev_attrib_attrs	= fileio_backend_dev_attrs,
 };
 
 static int __init fileio_module_init(void)
 {
-	struct target_backend_cits *tbc = &fileio_template.tb_cits;
-
-	target_core_setup_sub_cits(&fileio_template);
-	tbc->tb_dev_attrib_cit.ct_attrs = fileio_backend_dev_attrs;
-
-	return transport_subsystem_register(&fileio_template);
+	return transport_backend_register(&fileio_ops);
 }
 
 static void __exit fileio_module_exit(void)
 {
-	transport_subsystem_release(&fileio_template);
+	target_backend_unregister(&fileio_ops);
 }
 
 MODULE_DESCRIPTION("TCM FILEIO subsystem plugin");
diff --git a/drivers/target/target_core_hba.c b/drivers/target/target_core_hba.c
index e6e496ff9546..62ea4e8e70a8 100644
--- a/drivers/target/target_core_hba.c
+++ b/drivers/target/target_core_hba.c
@@ -39,63 +39,75 @@
 
 #include "target_core_internal.h"
 
-static LIST_HEAD(subsystem_list);
-static DEFINE_MUTEX(subsystem_mutex);
+static LIST_HEAD(backend_list);
+static DEFINE_MUTEX(backend_mutex);
 
 static u32 hba_id_counter;
 
 static DEFINE_SPINLOCK(hba_lock);
 static LIST_HEAD(hba_list);
 
-int transport_subsystem_register(struct se_subsystem_api *sub_api)
-{
-	struct se_subsystem_api *s;
-
-	INIT_LIST_HEAD(&sub_api->sub_api_list);
 
-	mutex_lock(&subsystem_mutex);
-	list_for_each_entry(s, &subsystem_list, sub_api_list) {
-		if (!strcmp(s->name, sub_api->name)) {
-			pr_err("%p is already registered with"
-				" duplicate name %s, unable to process"
-				" request\n", s, s->name);
-			mutex_unlock(&subsystem_mutex);
+int transport_backend_register(const struct target_backend_ops *ops)
+{
+	struct target_backend *tb, *old;
+
+	tb = kzalloc(sizeof(*tb), GFP_KERNEL);
+	if (!tb)
+		return -ENOMEM;
+	tb->ops = ops;
+
+	mutex_lock(&backend_mutex);
+	list_for_each_entry(old, &backend_list, list) {
+		if (!strcmp(old->ops->name, ops->name)) {
+			pr_err("backend %s already registered.\n", ops->name);
+			mutex_unlock(&backend_mutex);
+			kfree(tb);
 			return -EEXIST;
 		}
 	}
-	list_add_tail(&sub_api->sub_api_list, &subsystem_list);
-	mutex_unlock(&subsystem_mutex);
+	target_setup_backend_cits(tb);
+	list_add_tail(&tb->list, &backend_list);
+	mutex_unlock(&backend_mutex);
 
-	pr_debug("TCM: Registered subsystem plugin: %s struct module:"
-			" %p\n", sub_api->name, sub_api->owner);
+	pr_debug("TCM: Registered subsystem plugin: %s struct module: %p\n",
+			ops->name, ops->owner);
 	return 0;
 }
-EXPORT_SYMBOL(transport_subsystem_register);
+EXPORT_SYMBOL(transport_backend_register);
 
-void transport_subsystem_release(struct se_subsystem_api *sub_api)
+void target_backend_unregister(const struct target_backend_ops *ops)
 {
-	mutex_lock(&subsystem_mutex);
-	list_del(&sub_api->sub_api_list);
-	mutex_unlock(&subsystem_mutex);
+	struct target_backend *tb;
+
+	mutex_lock(&backend_mutex);
+	list_for_each_entry(tb, &backend_list, list) {
+		if (tb->ops == ops) {
+			list_del(&tb->list);
+			kfree(tb);
+			break;
+		}
+	}
+	mutex_unlock(&backend_mutex);
 }
-EXPORT_SYMBOL(transport_subsystem_release);
+EXPORT_SYMBOL(target_backend_unregister);
 
-static struct se_subsystem_api *core_get_backend(const char *sub_name)
+static struct target_backend *core_get_backend(const char *name)
 {
-	struct se_subsystem_api *s;
+	struct target_backend *tb;
 
-	mutex_lock(&subsystem_mutex);
-	list_for_each_entry(s, &subsystem_list, sub_api_list) {
-		if (!strcmp(s->name, sub_name))
+	mutex_lock(&backend_mutex);
+	list_for_each_entry(tb, &backend_list, list) {
+		if (!strcmp(tb->ops->name, name))
 			goto found;
 	}
-	mutex_unlock(&subsystem_mutex);
+	mutex_unlock(&backend_mutex);
 	return NULL;
 found:
-	if (s->owner && !try_module_get(s->owner))
-		s = NULL;
-	mutex_unlock(&subsystem_mutex);
-	return s;
+	if (tb->ops->owner && !try_module_get(tb->ops->owner))
+		tb = NULL;
+	mutex_unlock(&backend_mutex);
+	return tb;
 }
 
 struct se_hba *
@@ -116,13 +128,13 @@ core_alloc_hba(const char *plugin_name, u32 plugin_dep_id, u32 hba_flags)
 	hba->hba_index = scsi_get_new_index(SCSI_INST_INDEX);
 	hba->hba_flags |= hba_flags;
 
-	hba->transport = core_get_backend(plugin_name);
-	if (!hba->transport) {
+	hba->backend = core_get_backend(plugin_name);
+	if (!hba->backend) {
 		ret = -EINVAL;
 		goto out_free_hba;
 	}
 
-	ret = hba->transport->attach_hba(hba, plugin_dep_id);
+	ret = hba->backend->ops->attach_hba(hba, plugin_dep_id);
 	if (ret < 0)
 		goto out_module_put;
 
@@ -137,8 +149,8 @@ core_alloc_hba(const char *plugin_name, u32 plugin_dep_id, u32 hba_flags)
 	return hba;
 
 out_module_put:
-	module_put(hba->transport->owner);
-	hba->transport = NULL;
+	module_put(hba->backend->ops->owner);
+	hba->backend = NULL;
 out_free_hba:
 	kfree(hba);
 	return ERR_PTR(ret);
@@ -149,7 +161,7 @@ core_delete_hba(struct se_hba *hba)
 {
 	WARN_ON(hba->dev_count);
 
-	hba->transport->detach_hba(hba);
+	hba->backend->ops->detach_hba(hba);
 
 	spin_lock(&hba_lock);
 	list_del(&hba->hba_node);
@@ -158,9 +170,9 @@ core_delete_hba(struct se_hba *hba)
 	pr_debug("CORE_HBA[%d] - Detached HBA from Generic Target"
 			" Core\n", hba->hba_id);
 
-	module_put(hba->transport->owner);
+	module_put(hba->backend->ops->owner);
 
-	hba->transport = NULL;
+	hba->backend = NULL;
 	kfree(hba);
 	return 0;
 }
diff --git a/drivers/target/target_core_iblock.c b/drivers/target/target_core_iblock.c
index 8c965683789f..79f651fb98fb 100644
--- a/drivers/target/target_core_iblock.c
+++ b/drivers/target/target_core_iblock.c
@@ -54,12 +54,6 @@ static inline struct iblock_dev *IBLOCK_DEV(struct se_device *dev)
 }
 
 
-static struct se_subsystem_api iblock_template;
-
-/*	iblock_attach_hba(): (Part of se_subsystem_api_t template)
- *
- *
- */
 static int iblock_attach_hba(struct se_hba *hba, u32 host_id)
 {
 	pr_debug("CORE_HBA[%d] - TCM iBlock HBA Driver %s on"
@@ -899,7 +893,7 @@ static struct configfs_attribute *iblock_backend_dev_attrs[] = {
 	NULL,
 };
 
-static struct se_subsystem_api iblock_template = {
+static const struct target_backend_ops iblock_ops = {
 	.name			= "iblock",
 	.inquiry_prod		= "IBLOCK",
 	.inquiry_rev		= IBLOCK_VERSION,
@@ -919,21 +913,17 @@ static struct se_subsystem_api iblock_template = {
 	.get_io_min		= iblock_get_io_min,
 	.get_io_opt		= iblock_get_io_opt,
 	.get_write_cache	= iblock_get_write_cache,
+	.tb_dev_attrib_attrs	= iblock_backend_dev_attrs,
 };
 
 static int __init iblock_module_init(void)
 {
-	struct target_backend_cits *tbc = &iblock_template.tb_cits;
-
-	target_core_setup_sub_cits(&iblock_template);
-	tbc->tb_dev_attrib_cit.ct_attrs = iblock_backend_dev_attrs;
-
-	return transport_subsystem_register(&iblock_template);
+	return transport_backend_register(&iblock_ops);
 }
 
 static void __exit iblock_module_exit(void)
 {
-	transport_subsystem_release(&iblock_template);
+	target_backend_unregister(&iblock_ops);
 }
 
 MODULE_DESCRIPTION("TCM IBLOCK subsystem plugin");
diff --git a/drivers/target/target_core_internal.h b/drivers/target/target_core_internal.h
index ce80ca76f68b..01181aed67dc 100644
--- a/drivers/target/target_core_internal.h
+++ b/drivers/target/target_core_internal.h
@@ -1,6 +1,19 @@
 #ifndef TARGET_CORE_INTERNAL_H
 #define TARGET_CORE_INTERNAL_H
 
+struct target_backend {
+	struct list_head list;
+
+	const struct target_backend_ops *ops;
+
+	struct config_item_type tb_dev_cit;
+	struct config_item_type tb_dev_attrib_cit;
+	struct config_item_type tb_dev_pr_cit;
+	struct config_item_type tb_dev_wwn_cit;
+	struct config_item_type tb_dev_alua_tg_pt_gps_cit;
+	struct config_item_type tb_dev_stat_cit;
+};
+
 /* target_core_alua.c */
 extern struct t10_alua_lu_gp *default_lu_gp;
 
@@ -40,6 +53,9 @@ struct se_device *target_alloc_device(struct se_hba *hba, const char *name);
 int	target_configure_device(struct se_device *dev);
 void	target_free_device(struct se_device *);
 
+/* target_core_configfs.c */
+void	target_setup_backend_cits(struct target_backend *);
+
 /* target_core_fabric_lib.c */
 int	target_get_pr_transport_id_len(struct se_node_acl *nacl,
 		struct t10_pr_registration *pr_reg, int *format_code);
diff --git a/drivers/target/target_core_pscsi.c b/drivers/target/target_core_pscsi.c
index 21db991b4465..2e3a0b004f9a 100644
--- a/drivers/target/target_core_pscsi.c
+++ b/drivers/target/target_core_pscsi.c
@@ -57,8 +57,6 @@ static inline struct pscsi_dev_virt *PSCSI_DEV(struct se_device *dev)
 	return container_of(dev, struct pscsi_dev_virt, dev);
 }
 
-static struct se_subsystem_api pscsi_template;
-
 static sense_reason_t pscsi_execute_cmd(struct se_cmd *cmd);
 static void pscsi_req_done(struct request *, int);
 
@@ -1141,7 +1139,7 @@ static struct configfs_attribute *pscsi_backend_dev_attrs[] = {
 	NULL,
 };
 
-static struct se_subsystem_api pscsi_template = {
+static const struct target_backend_ops pscsi_ops = {
 	.name			= "pscsi",
 	.owner			= THIS_MODULE,
 	.transport_flags	= TRANSPORT_FLAG_PASSTHROUGH,
@@ -1157,21 +1155,17 @@ static struct se_subsystem_api pscsi_template = {
 	.show_configfs_dev_params = pscsi_show_configfs_dev_params,
 	.get_device_type	= pscsi_get_device_type,
 	.get_blocks		= pscsi_get_blocks,
+	.tb_dev_attrib_attrs	= pscsi_backend_dev_attrs,
 };
 
 static int __init pscsi_module_init(void)
 {
-	struct target_backend_cits *tbc = &pscsi_template.tb_cits;
-
-	target_core_setup_sub_cits(&pscsi_template);
-	tbc->tb_dev_attrib_cit.ct_attrs = pscsi_backend_dev_attrs;
-
-	return transport_subsystem_register(&pscsi_template);
+	return transport_backend_register(&pscsi_ops);
 }
 
 static void __exit pscsi_module_exit(void)
 {
-	transport_subsystem_release(&pscsi_template);
+	target_backend_unregister(&pscsi_ops);
 }
 
 MODULE_DESCRIPTION("TCM PSCSI subsystem plugin");
diff --git a/drivers/target/target_core_rd.c b/drivers/target/target_core_rd.c
index 55315fd0f5d3..cf443a8a3cbe 100644
--- a/drivers/target/target_core_rd.c
+++ b/drivers/target/target_core_rd.c
@@ -43,10 +43,6 @@ static inline struct rd_dev *RD_DEV(struct se_device *dev)
 	return container_of(dev, struct rd_dev, dev);
 }
 
-/*	rd_attach_hba(): (Part of se_subsystem_api_t template)
- *
- *
- */
 static int rd_attach_hba(struct se_hba *hba, u32 host_id)
 {
 	struct rd_host *rd_host;
@@ -735,7 +731,7 @@ static struct configfs_attribute *rd_mcp_backend_dev_attrs[] = {
 	NULL,
 };
 
-static struct se_subsystem_api rd_mcp_template = {
+static const struct target_backend_ops rd_mcp_ops = {
 	.name			= "rd_mcp",
 	.inquiry_prod		= "RAMDISK-MCP",
 	.inquiry_rev		= RD_MCP_VERSION,
@@ -751,25 +747,15 @@ static struct se_subsystem_api rd_mcp_template = {
 	.get_blocks		= rd_get_blocks,
 	.init_prot		= rd_init_prot,
 	.free_prot		= rd_free_prot,
+	.tb_dev_attrib_attrs	= rd_mcp_backend_dev_attrs,
 };
 
 int __init rd_module_init(void)
 {
-	struct target_backend_cits *tbc = &rd_mcp_template.tb_cits;
-	int ret;
-
-	target_core_setup_sub_cits(&rd_mcp_template);
-	tbc->tb_dev_attrib_cit.ct_attrs = rd_mcp_backend_dev_attrs;
-
-	ret = transport_subsystem_register(&rd_mcp_template);
-	if (ret < 0) {
-		return ret;
-	}
-
-	return 0;
+	return transport_backend_register(&rd_mcp_ops);
 }
 
 void rd_module_exit(void)
 {
-	transport_subsystem_release(&rd_mcp_template);
+	target_backend_unregister(&rd_mcp_ops);
 }
diff --git a/drivers/target/target_core_user.c b/drivers/target/target_core_user.c
index 60330e00f59d..fb67e313dc4f 100644
--- a/drivers/target/target_core_user.c
+++ b/drivers/target/target_core_user.c
@@ -1115,7 +1115,7 @@ static struct configfs_attribute *tcmu_backend_dev_attrs[] = {
 	NULL,
 };
 
-static struct se_subsystem_api tcmu_template = {
+static const struct target_backend_ops tcmu_ops = {
 	.name			= "user",
 	.inquiry_prod		= "USER",
 	.inquiry_rev		= TCMU_VERSION,
@@ -1131,11 +1131,11 @@ static struct se_subsystem_api tcmu_template = {
 	.show_configfs_dev_params = tcmu_show_configfs_dev_params,
 	.get_device_type	= sbc_get_device_type,
 	.get_blocks		= tcmu_get_blocks,
+	.tb_dev_attrib_attrs	= tcmu_backend_dev_attrs,
 };
 
 static int __init tcmu_module_init(void)
 {
-	struct target_backend_cits *tbc = &tcmu_template.tb_cits;
 	int ret;
 
 	BUILD_BUG_ON((sizeof(struct tcmu_cmd_entry) % TCMU_OP_ALIGN_SIZE) != 0);
@@ -1158,10 +1158,7 @@ static int __init tcmu_module_init(void)
 		goto out_unreg_device;
 	}
 
-	target_core_setup_sub_cits(&tcmu_template);
-	tbc->tb_dev_attrib_cit.ct_attrs = tcmu_backend_dev_attrs;
-
-	ret = transport_subsystem_register(&tcmu_template);
+	ret = transport_backend_register(&tcmu_ops);
 	if (ret)
 		goto out_unreg_genl;
 
@@ -1179,7 +1176,7 @@ out_free_cache:
 
 static void __exit tcmu_module_exit(void)
 {
-	transport_subsystem_release(&tcmu_template);
+	target_backend_unregister(&tcmu_ops);
 	genl_unregister_family(&tcmu_genl_family);
 	root_device_unregister(tcmu_root_device);
 	kmem_cache_destroy(tcmu_cmd_cache);
diff --git a/include/target/target_core_backend.h b/include/target/target_core_backend.h
index 80d9e486e33e..514b52019380 100644
--- a/include/target/target_core_backend.h
+++ b/include/target/target_core_backend.h
@@ -3,18 +3,7 @@
 
 #define TRANSPORT_FLAG_PASSTHROUGH		1
 
-struct target_backend_cits {
-	struct config_item_type tb_dev_cit;
-	struct config_item_type tb_dev_attrib_cit;
-	struct config_item_type tb_dev_pr_cit;
-	struct config_item_type tb_dev_wwn_cit;
-	struct config_item_type tb_dev_alua_tg_pt_gps_cit;
-	struct config_item_type tb_dev_stat_cit;
-};
-
-struct se_subsystem_api {
-	struct list_head sub_api_list;
-
+struct target_backend_ops {
 	char name[16];
 	char inquiry_prod[16];
 	char inquiry_rev[4];
@@ -52,7 +41,7 @@ struct se_subsystem_api {
 	int (*format_prot)(struct se_device *);
 	void (*free_prot)(struct se_device *);
 
-	struct target_backend_cits tb_cits;
+	struct configfs_attribute **tb_dev_attrib_attrs;
 };
 
 struct sbc_ops {
@@ -64,8 +53,8 @@ struct sbc_ops {
 	sense_reason_t (*execute_unmap)(struct se_cmd *cmd);
 };
 
-int	transport_subsystem_register(struct se_subsystem_api *);
-void	transport_subsystem_release(struct se_subsystem_api *);
+int	transport_backend_register(const struct target_backend_ops *);
+void	target_backend_unregister(const struct target_backend_ops *);
 
 void	target_complete_cmd(struct se_cmd *, u8);
 void	target_complete_cmd_with_length(struct se_cmd *, u8, int);
@@ -103,9 +92,6 @@ sense_reason_t	transport_generic_map_mem_to_cmd(struct se_cmd *,
 
 bool	target_lun_is_rdonly(struct se_cmd *);
 
-/* From target_core_configfs.c to setup default backend config_item_types */
-void	target_core_setup_sub_cits(struct se_subsystem_api *);
-
 /* attribute helpers from target_core_device.c for backend drivers */
 bool	se_dev_check_wce(struct se_device *);
 int	se_dev_set_max_unmap_lba_count(struct se_device *, u32);
diff --git a/include/target/target_core_base.h b/include/target/target_core_base.h
index 78ed2a83838c..03e2ee8f8337 100644
--- a/include/target/target_core_base.h
+++ b/include/target/target_core_base.h
@@ -797,7 +797,7 @@ struct se_device {
 #define SE_UDEV_PATH_LEN 512		/* must be less than PAGE_SIZE */
 	unsigned char		udev_path[SE_UDEV_PATH_LEN];
 	/* Pointer to template of function pointers for transport */
-	struct se_subsystem_api *transport;
+	const struct target_backend_ops *transport;
 	/* Linked list for struct se_hba struct se_device list */
 	struct list_head	dev_list;
 	struct se_lun		xcopy_lun;
@@ -819,7 +819,7 @@ struct se_hba {
 	spinlock_t		device_lock;
 	struct config_group	hba_group;
 	struct mutex		hba_access_mutex;
-	struct se_subsystem_api *transport;
+	struct target_backend	*backend;
 };
 
 struct scsi_port_stats {