[PATCH 1/2] nvmet: avoid recursive configfs open for file-backed namespaces

[Christoph Hellwig]

> +	ret = kern_path(ns->device_path, LOOKUP_FOLLOW, &path);
> +	if (ret) {
> +		pr_err("failed to open file %s: (%d)\n",
> +		       ns->device_path, ret);
> +		return ret;
> +	}
> +
> +	if (!strcmp(path.dentry->d_sb->s_type->name, "configfs")) {
> +		pr_err("configfs paths cannot back namespace %s\n",
> +		       ns->device_path);
> +		path_put(&path);
> +		return -EINVAL;
> +	}

String comparisons are a bit weird, checking the actual file_system_type
is a lot cheaper and more safe.  And please move this into a helper
in configfs as I bet there are tons of other users like this and they'd
benefit fro ma common helper.