[v2,2/3] docs/nvdimm: add description of alignment requirement of device dax

For device dax (e.g., /dev/dax0.0), the NUM of 'align=NUM' option
needs to match the alignment requirement of the device dax.
It must be larger than or equal to the 'align' of device dax.

Signed-off-by: Jingqi Liu <jingqi.liu@intel.com>
---
 docs/nvdimm.txt | 9 +++++++++
 1 file changed, 9 insertions(+)

On 4/15/20 4:35 AM, Jingqi Liu wrote:
> For device dax (e.g., /dev/dax0.0), the NUM of 'align=NUM' option
> needs to match the alignment requirement of the device dax.
> It must be larger than or equal to the 'align' of device dax.
> 
> Signed-off-by: Jingqi Liu <jingqi.liu@intel.com>
> ---
>  docs/nvdimm.txt | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/docs/nvdimm.txt b/docs/nvdimm.txt
> index 362e99109e..3c7b6dab5f 100644
> --- a/docs/nvdimm.txt
> +++ b/docs/nvdimm.txt
> @@ -132,6 +132,15 @@ address to the page size (getpagesize(2)) by default. However, some
>  types of backends may require an alignment different than the page
>  size. In that case, QEMU v2.12.0 and later provide 'align' option to
>  memory-backend-file to allow users to specify the proper alignment.
> +For device dax (e.g., /dev/dax0.0), this alignment needs to match the
> +alignment requirement of the device dax. The NUM of 'align=NUM' option
> +must be larger than or equal to the 'align' of device dax.
> +We can use the following command to show the 'align' of device dax.
> +
> +    ndctl list -X
> +
> +In order to get the proper 'align' of device dax, you need to install
> +the library 'libdaxctl'.
>  
>  For example, device dax require the 2 MB alignment, so we can use
>  following QEMU command line options to use it (/dev/dax0.0) as the
> 

Given that this series introduces support for libdaxctl, perhaps suggesting in
the docs how you can also query the @align with daxctl tool? e.g.

"We can one of the following commands to show the 'align' of device dax:

     ndctl list -X
     daxctl list -R"

The unlikely reason being that users may only install daxctl-{,libs,devel} and
not ndctl-*. It also covers other users like ACPI HMAT/hmem which are not
instrumented with ndctl.

With that:

  Reviewed-by: Joao Martins <joao.m.martins@oracle.com>

	Joao

On 4/29/2020 12:22 AM, Joao Martins wrote:
> On 4/15/20 4:35 AM, Jingqi Liu wrote:
>> For device dax (e.g., /dev/dax0.0), the NUM of 'align=NUM' option
>> needs to match the alignment requirement of the device dax.
>> It must be larger than or equal to the 'align' of device dax.
>>
>> Signed-off-by: Jingqi Liu <jingqi.liu@intel.com>
>> ---
>>   docs/nvdimm.txt | 9 +++++++++
>>   1 file changed, 9 insertions(+)
>>
>> diff --git a/docs/nvdimm.txt b/docs/nvdimm.txt
>> index 362e99109e..3c7b6dab5f 100644
>> --- a/docs/nvdimm.txt
>> +++ b/docs/nvdimm.txt
>> @@ -132,6 +132,15 @@ address to the page size (getpagesize(2)) by default. However, some
>>   types of backends may require an alignment different than the page
>>   size. In that case, QEMU v2.12.0 and later provide 'align' option to
>>   memory-backend-file to allow users to specify the proper alignment.
>> +For device dax (e.g., /dev/dax0.0), this alignment needs to match the
>> +alignment requirement of the device dax. The NUM of 'align=NUM' option
>> +must be larger than or equal to the 'align' of device dax.
>> +We can use the following command to show the 'align' of device dax.
>> +
>> +    ndctl list -X
>> +
>> +In order to get the proper 'align' of device dax, you need to install
>> +the library 'libdaxctl'.
>>   
>>   For example, device dax require the 2 MB alignment, so we can use
>>   following QEMU command line options to use it (/dev/dax0.0) as the
>>
> Given that this series introduces support for libdaxctl, perhaps suggesting in
> the docs how you can also query the @align with daxctl tool? e.g.
>
> "We can one of the following commands to show the 'align' of device dax:
>
>       ndctl list -X
>       daxctl list -R"

Thanks for your comments.
I'll add "daxctl list -R" in this doc.

Jingqi

> The unlikely reason being that users may only install daxctl-{,libs,devel} and
> not ndctl-*. It also covers other users like ACPI HMAT/hmem which are not
> instrumented with ndctl.
>
> With that:
>
>    Reviewed-by: Joao Martins <joao.m.martins@oracle.com>
>
> 	Joao

Thanks.