Re: [Qemu-devel] [PATCH] docs/nvdimm: add example on persistent backend setup

[Stefan Hajnoczi <stefanha@gmail.com>]

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On Wed, Jul 24, 2019 at 03:03:07PM +0800, Wei Yang wrote:
> Persistent backend setup requires some knowledge about nvdimm and ndctl
> tool. Some users report they may struggle to gather these knowledge and
> have difficulty to setup it properly.
> 
> Here we provide two examples for persistent backend and gives the link
> to ndctl. By doing so, user could try it directly and do more
> investigation on persistent backend setup with ndctl.
> 
> Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>
> ---
>  docs/nvdimm.txt | 28 ++++++++++++++++++++++++++++
>  1 file changed, 28 insertions(+)
> 
> diff --git a/docs/nvdimm.txt b/docs/nvdimm.txt
> index b531cacd35..baba7a940d 100644
> --- a/docs/nvdimm.txt
> +++ b/docs/nvdimm.txt
> @@ -171,6 +171,32 @@ guest software that this vNVDIMM device contains a region that cannot
>  accept persistent writes. In result, for example, the guest Linux
>  NVDIMM driver, marks such vNVDIMM device as read-only.
>  
> +Backend File Setup Example
> +..........................

For consistency with the rest of the document please use '-' instead of
'.'.

> +
> +Here is two examples for how to setup these persistent backend on
> +linux, which leverages the tool ndctl [3].

Small grammar tweaks:

  Here are two examples showing how to set up persistent backends on
  Linux using the tool ndctl [3].

> +
> +It is easy to setup DAX device backend file.

Please move this into the "A. DAX device" section and use it as an
introduction to explain what this section is about:

  Use the following command to set up /dev/dax0.0 so that the entirety
  of namespace0.0 can be exposed as an emulated NVDIMM to the guest:

> +
> +A. DAX device
> +
> +    ndctl create-namespace -f -e namespace0.0 -m devdax
> +
> +The /dev/dax0.0 could be used directly in "mem-path" option.
> +
> +For DAX file, it is more than creating the proper namespace. The
> +block device should be partitioned and mounted (with dax option).

Please move this into "B. DAX file":

  Individual files on a DAX host file system can be exposed as emulated
  NVDIMMS.  First an fsdax block device is created, partitioned, and
  then mounted with the "dax" mount option:

> +
> +B. DAX file
> +
> +    ndctl create-namespace -f -e namespace0.0 -m fsdax
> +    (partition /dev/pmem0 with name pmem0p1)
> +    mount -o dax /dev/pmem0p1 /mnt
> +    (dd a file with proper size in /mnt)

"dd a file" could be "create or copy a disk image file with qemu-img(1),
cp(1), or dd(1) in /mnt".

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