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

[Pankaj Gupta <pagupta@redhat.com>]

> >
> >> 
> >> 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
> >> +..........................
> >> +
> >> +Here is two examples for how to setup these persistent backend on
> >> +linux, which leverages the tool ndctl [3].
> >> +
> >> +It is easy to setup DAX device backend file.
> >> +
> >> +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).
> >> +
> >> +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)
> >
> 
> Hi, Pankaj
> 
> Thanks for your comment.
> 
> >This namespace is for filesystem DAX? What if user wants to create namespace
> >for
> >device DAX to be used as persistent backend?
> >
> 
> User could choose the type (devdax/fsdax) in ndctl command line with -m
> option.

yes.

> 
> >Does this makes sense to mention about by default namespace created on
> >persistent
> >backend?
> >
> 
> I don't get your point. Here is an example to let user know how to create
> persistent backend. In case they want to get more control about the backend,
> they can refer to the ndctl link.

I agree this is helpful for users. 

> 
> You mean it is not proper to mention the backend setup example in the
> document? We found many users come to us for how to setup it, so we decide to
> add this section.

Sorry! For some reason I ignored devicedax namespace information in patch.
The patch looks good to me and I agree its helpful for the users.
   

Thanks,
Pankaj

> 
> Do you have other option?
> 
> >Thanks,
> >Pankaj
> >
> >> +
> >> +Then the new file in /mnt could be used in "mem-path" option.
> >> +
> >>  NVDIMM Persistence
> >>  ------------------
> >>  
> >> @@ -212,3 +238,5 @@ References
> >>      https://www.snia.org/sites/default/files/technical_work/final/NVMProgrammingModel_v1.2.pdf
> >>  [2] Persistent Memory Development Kit (PMDK), formerly known as NVML
> >>  project, home page:
> >>      http://pmem.io/pmdk/
> >> +[3] ndctl-create-namespace - provision or reconfigure a namespace
> >> +    http://pmem.io/ndctl/ndctl-create-namespace.html
> >> --
> >> 2.17.1
> >> 
> >> 
> >> 
> 
> --
> Wei Yang
> Help you, Help me
> 
>