Re: [Qemu-devel] [RFC PATCH 2/4] nvdimm: add functions to initialize and perform flush on back store

[Xiao Guangrong <guangrong.xiao@gmail.com>]

On 03/31/2017 04:41 PM, Haozhong Zhang wrote:
> fsync() is used to persist modifications to the back store. If the
> host NVDIMM is used as the back store, fsync() on Linux will trigger
> the write to the host flush hint address.
>
> Signed-off-by: Haozhong Zhang <haozhong.zhang@intel.com>
> ---
>  hw/mem/nvdimm.c         | 22 ++++++++++++++++++++++
>  include/hw/mem/nvdimm.h | 13 +++++++++++++
>  2 files changed, 35 insertions(+)
>
> diff --git a/hw/mem/nvdimm.c b/hw/mem/nvdimm.c
> index db896b0..484ab8b 100644
> --- a/hw/mem/nvdimm.c
> +++ b/hw/mem/nvdimm.c
> @@ -78,6 +78,26 @@ static MemoryRegion *nvdimm_get_memory_region(PCDIMMDevice *dimm)
>      return &nvdimm->nvdimm_mr;
>  }
>
> +static void nvdimm_flush_init(NVDIMMDevice *nvdimm, MemoryRegion *hostmem_mr)
> +{
> +    if (nvdimm->flush_hint_enabled) {
> +        nvdimm->backend_fd = memory_region_get_fd(hostmem_mr);

Hmm, IIRC host-mem-file does not initalize backend_fd at all.