nvmet: introduce the passthru configfs interface

When CONFIG_NVME_TARGET_PASSTHRU as 'passthru' directory will
be added to each subsystem. The directory is similar to a namespace
and has two attributes: device_path and enable. The user must set the
path to the nvme controller's char device and write '1' to enable the
subsystem to use passthru.

Any given subsystem is prevented from enabling both a regular namespace
and the passthru device. If one is enabled, enabling the other will
produce an error.
Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Reviewed-by: Keith Busch <kbusch@kernel.org>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Christoph Hellwig <hch@lst.de>

drivers/nvme/target/configfs.c

@@ -666,6 +666,103 @@ static const struct config_item_type nvmet_namespaces_type = {
 	.ct_owner		= THIS_MODULE,
 };
 
+#ifdef CONFIG_NVME_TARGET_PASSTHRU
+
+static ssize_t nvmet_passthru_device_path_show(struct config_item *item,
+		char *page)
+{
+	struct nvmet_subsys *subsys = to_subsys(item->ci_parent);
+
+	return snprintf(page, PAGE_SIZE, "%s\n", subsys->passthru_ctrl_path);
+}
+
+static ssize_t nvmet_passthru_device_path_store(struct config_item *item,
+		const char *page, size_t count)
+{
+	struct nvmet_subsys *subsys = to_subsys(item->ci_parent);
+	size_t len;
+	int ret;
+
+	mutex_lock(&subsys->lock);
+
+	ret = -EBUSY;
+	if (subsys->passthru_ctrl)
+		goto out_unlock;
+
+	ret = -EINVAL;
+	len = strcspn(page, "\n");
+	if (!len)
+		goto out_unlock;
+
+	kfree(subsys->passthru_ctrl_path);
+	ret = -ENOMEM;
+	subsys->passthru_ctrl_path = kstrndup(page, len, GFP_KERNEL);
+	if (!subsys->passthru_ctrl_path)
+		goto out_unlock;
+
+	mutex_unlock(&subsys->lock);
+
+	return count;
+out_unlock:
+	mutex_unlock(&subsys->lock);
+	return ret;
+}
+CONFIGFS_ATTR(nvmet_passthru_, device_path);
+
+static ssize_t nvmet_passthru_enable_show(struct config_item *item,
+		char *page)
+{
+	struct nvmet_subsys *subsys = to_subsys(item->ci_parent);
+
+	return sprintf(page, "%d\n", subsys->passthru_ctrl ? 1 : 0);
+}
+
+static ssize_t nvmet_passthru_enable_store(struct config_item *item,
+		const char *page, size_t count)
+{
+	struct nvmet_subsys *subsys = to_subsys(item->ci_parent);
+	bool enable;
+	int ret = 0;
+
+	if (strtobool(page, &enable))
+		return -EINVAL;
+
+	if (enable)
+		ret = nvmet_passthru_ctrl_enable(subsys);
+	else
+		nvmet_passthru_ctrl_disable(subsys);
+
+	return ret ? ret : count;
+}
+CONFIGFS_ATTR(nvmet_passthru_, enable);
+
+static struct configfs_attribute *nvmet_passthru_attrs[] = {
+	&nvmet_passthru_attr_device_path,
+	&nvmet_passthru_attr_enable,
+	NULL,
+};
+
+static const struct config_item_type nvmet_passthru_type = {
+	.ct_attrs		= nvmet_passthru_attrs,
+	.ct_owner		= THIS_MODULE,
+};
+
+static void nvmet_add_passthru_group(struct nvmet_subsys *subsys)
+{
+	config_group_init_type_name(&subsys->passthru_group,
+				    "passthru", &nvmet_passthru_type);
+	configfs_add_default_group(&subsys->passthru_group,
+				   &subsys->group);
+}
+
+#else /* CONFIG_NVME_TARGET_PASSTHRU */
+
+static void nvmet_add_passthru_group(struct nvmet_subsys *subsys)
+{
+}
+
+#endif /* CONFIG_NVME_TARGET_PASSTHRU */
+
 static int nvmet_port_subsys_allow_link(struct config_item *parent,
 		struct config_item *target)
 {
@@ -1125,6 +1222,8 @@ static struct config_group *nvmet_subsys_make(struct config_group *group,
 	configfs_add_default_group(&subsys->allowed_hosts_group,
 			&subsys->group);
 
+	nvmet_add_passthru_group(subsys);
+
 	return &subsys->group;
 }
 

drivers/nvme/target/nvmet.h

@@ -248,6 +248,7 @@ struct nvmet_subsys {
 #ifdef CONFIG_NVME_TARGET_PASSTHRU
 	struct nvme_ctrl	*passthru_ctrl;
 	char			*passthru_ctrl_path;
+	struct config_group	passthru_group;
 #endif /* CONFIG_NVME_TARGET_PASSTHRU */
 };