Re: [Qemu-devel] [PATCH 00/15] NVDIMM: introduce nvdimm label support

[Stefan Hajnoczi]

On Tue, Mar 22, 2016 at 08:37:40AM -0700, Dan Williams wrote:
> On Thu, Mar 17, 2016 at 3:04 AM, Stefan Hajnoczi <address@hidden> wrote:
> > On Thu, Mar 17, 2016 at 04:32:46PM +0800, Xiao Guangrong wrote:
> >> This patchset is against commit d4207b223eef3 (fw-cfg: support writeable
> >> blobs) on pci branch of Michael's git tree and can be found at:
> >>       https://github.com/xiaogr/qemu.git nvdimm-label-v1
> >>
> >> This is the last part of vNVDIMM implementation which introduces nvdimm
> >> label support
> >>
> >> Currently Linux NVDIMM driver does not support namespace operation on this
> >> kind of PMEM, apply below changes to support dynamical namespace:
> >>
> >> @@ -798,7 +823,8 @@ static int acpi_nfit_register_dimms(struct 
> >> acpi_nfit_desc *a
> >>                         continue;
> >>                 }
> >>
> >> -               if (nfit_mem->bdw && nfit_mem->memdev_pmem)
> >> +               //if (nfit_mem->bdw && nfit_mem->memdev_pmem)
> >> +               if (nfit_mem->memdev_pmem)
> >>                         flags |= NDD_ALIASING;
> >
> > Not a blocker for this patch series, but why does Linux require Block
> > Device Window to enable namespace support?
> 
> A namespace label delineates aliased capacity between the pmem and
> block-window access mechanisms.  If there is no aliased capacity then
> the size of the namespace can be directly derived from the nfit range
> and a label need not be considered.  Contiguous (dax-capable)
> sub-divisions of pmem can be had via partitioning of the resulting
> gendisk.

Xiao Guangrong: Given this new information, what is the purpose of the
QEMU patches for ACPI DSM and especially the namespace label support?

The QEMU NVDIMM device only supports pmem so now I'm not sure we need
namespace labels or the ACPI DSM at all.

Stefan

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