scsi: target: core: Add common tpg/enable attribute

Many fabric modules provide their own implementation of enable attribute in
tpg.

Provide a way to remove code duplication in the fabric modules and
automatically add "enable" attribute if a fabric module has an
implementation of fabric_enable_tpg().

Link: https://lore.kernel.org/r/[e-mail]
Reviewed-by: Roman Bolshakov <[e-mail]>
Reviewed-by: Mike Christie <[e-mail]>
Signed-off-by: Dmitry Bogdanov <[e-mail]>
Signed-off-by: Martin K. Petersen <[e-mail]>

drivers/target/target_core_configfs.c

···
 			 * fabric driver unload of TFO->module to proceed.
 			 */
 			rcu_barrier();
+			kfree(t->tf_tpg_base_cit.ct_attrs);
 			kfree(t);
 			return;
 		}

drivers/target/target_core_fabric_configfs.c

···
 	.release		= target_fabric_tpg_release,
 };
 
-TF_CIT_SETUP_DRV(tpg_base, &target_fabric_tpg_base_item_ops, NULL);
+static ssize_t target_fabric_tpg_base_enable_show(struct config_item *item,
+						  char *page)
+{
+	return sysfs_emit(page, "%d\n", to_tpg(item)->enabled);
+}
 
+static ssize_t target_fabric_tpg_base_enable_store(struct config_item *item,
+						   const char *page,
+						   size_t count)
+{
+	struct se_portal_group *se_tpg = to_tpg(item);
+	int ret;
+	bool op;
+
+	ret = strtobool(page, &op);
+	if (ret)
+		return ret;
+
+	if (se_tpg->enabled == op)
+		return count;
+
+	ret = se_tpg->se_tpg_tfo->fabric_enable_tpg(se_tpg, op);
+	if (ret)
+		return ret;
+
+	se_tpg->enabled = op;
+
+	return count;
+}
+
+CONFIGFS_ATTR(target_fabric_tpg_base_, enable);
+
+static int
+target_fabric_setup_tpg_base_cit(struct target_fabric_configfs *tf)
+{
+	struct config_item_type *cit = &tf->tf_tpg_base_cit;
+	struct configfs_attribute **attrs = NULL;
+	size_t nr_attrs = 0;
+	int i = 0;
+
+	if (tf->tf_ops->tfc_tpg_base_attrs)
+		while (tf->tf_ops->tfc_tpg_base_attrs[nr_attrs] != NULL)
+			nr_attrs++;
+
+	if (tf->tf_ops->fabric_enable_tpg)
+		nr_attrs++;
+
+	if (nr_attrs == 0)
+		goto done;
+
+	/* + 1 for final NULL in the array */
+	attrs = kcalloc(nr_attrs + 1, sizeof(*attrs), GFP_KERNEL);
+	if (!attrs)
+		return -ENOMEM;
+
+	if (tf->tf_ops->tfc_tpg_base_attrs)
+		for (; tf->tf_ops->tfc_tpg_base_attrs[i] != NULL; i++)
+			attrs[i] = tf->tf_ops->tfc_tpg_base_attrs[i];
+
+	if (tf->tf_ops->fabric_enable_tpg)
+		attrs[i] = &target_fabric_tpg_base_attr_enable;
+
+done:
+	cit->ct_item_ops = &target_fabric_tpg_base_item_ops;
+	cit->ct_attrs = attrs;
+	cit->ct_owner = tf->tf_ops->module;
+	pr_debug("Setup generic tpg_base\n");
+
+	return 0;
+}
 /* End of tfc_tpg_base_cit */
 
 /* Start of tfc_tpg_cit */
···
 
 int target_fabric_setup_cits(struct target_fabric_configfs *tf)
 {
+	int ret;
+
 	target_fabric_setup_discovery_cit(tf);
 	target_fabric_setup_wwn_cit(tf);
 	target_fabric_setup_wwn_fabric_stats_cit(tf);
 	target_fabric_setup_wwn_param_cit(tf);
 	target_fabric_setup_tpg_cit(tf);
-	target_fabric_setup_tpg_base_cit(tf);
+
+	ret = target_fabric_setup_tpg_base_cit(tf);
+	if (ret)
+		return ret;
+
 	target_fabric_setup_tpg_port_cit(tf);
 	target_fabric_setup_tpg_port_stat_cit(tf);
 	target_fabric_setup_tpg_lun_cit(tf);

include/target/target_core_base.h

···
 	 * Negative values can be used by fabric drivers for internal use TPGs.
 	 */
 	int			proto_id;
+	bool			enabled;
 	/* Used for PR SPEC_I_PT=1 and REGISTER_AND_MOVE */
 	atomic_t		tpg_pr_ref_count;
 	/* Spinlock for adding/removing ACLed Nodes */

include/target/target_core_fabric.h

···
 	void (*add_wwn_groups)(struct se_wwn *);
 	struct se_portal_group *(*fabric_make_tpg)(struct se_wwn *,
 						   const char *);
+	int (*fabric_enable_tpg)(struct se_portal_group *se_tpg, bool enable);
 	void (*fabric_drop_tpg)(struct se_portal_group *);
 	int (*fabric_post_link)(struct se_portal_group *,
 				struct se_lun *);