Re: [Qemu-devel] [RESEND PATCH 1/2] nvdimm: warn if the backend is not a DAX device

[Xiao Guangrong]

On 05/26/2017 10:32 AM, Haozhong Zhang wrote:

> +static void nvdimm_check_dax(HostMemoryBackend *hostmem)
> +{
> +    char *mem_path =
> +        object_property_get_str(OBJECT(hostmem), "mem-path", NULL);
> +    char *dev_name = NULL, *sysfs_path = NULL;
> +    bool is_dax = false;
> +
> +    if (!mem_path) {
> +        goto out;
> +    }
> +
> +    if (!g_str_has_prefix(mem_path, "/dev/dax")) {
> +        goto out;
> +    }
> +
> +    dev_name = mem_path + strlen("/dev/");
> +    sysfs_path = g_strdup_printf("/sys/class/dax/%s", dev_name);
> +    if (access(sysfs_path, F_OK)) {
> +        goto out;
> +    }
> +
> +    is_dax = true;
> +

So only dax raw disk has write-persistence guaranty， a pre-allocated
file which locates on a DAX-enabled filesystem can not?