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

[Wei Yang]

On Wed, Jul 24, 2019 at 03:28:22AM -0400, Pankaj Gupta 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 <address@hidden>
>> ---
>>  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.

>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. 

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.

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