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

[Wei Yang]

On Wed, Jul 24, 2019 at 06:17:31AM -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)
>
>This is not clear to me. why 'dd' file is required in /mnt?
>You mean for creating a backend file?
>

Yes, create a backend file. You need to give a file instead of a directory to
qemu command line.

>> +
>> +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
>> --
>
>Looks good to me. Just a small comment above. 
>Other than that: Reviewed-by: Pankaj Gupta <address@hidden>
>

Thanks

>> 2.17.1
>> 
>> 
>> 

-- 
Wei Yang
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