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References: <20170526023213.18741-1-haozhong.zhang@intel.com>
From: Xiao Guangrong <guangrong.xiao@gmail.com>
Message-ID: <14af6adf-9076-1368-75bb-8001ed667150@gmail.com>
Date: Thu, 1 Jun 2017 20:00:34 +0800
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Subject: Re: [Qemu-devel] [RESEND PATCH 1/2] nvdimm: warn if the backend is
 not a DAX device
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To: Haozhong Zhang <haozhong.zhang@intel.com>, qemu-devel@nongnu.org
Cc: "Michael S. Tsirkin" <mst@redhat.com>, Igor Mammedov <imammedo@redhat.com>, Stefan Hajnoczi <stefanha@gmail.com>, Dan Williams <dan.j.williams@intel.com>



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?