[PATCH v4 04/11] block: define meta io descriptor

[Martin K. Petersen]

Christoph,

>> Not sure what to do about the storage tag. For Linux that would
>> probably be owned by the filesystem (as opposed to the application).
>> But I guess one could envision a userland application acting as a
>> storage target and in that case the tag would need to be passed to
>> the kernel.
>
> Right now the series only supports PI on the block device.  In that
> case the userspace application can clearly make use of it.  If we
> want to support PI on file systems (which I'd really like to do for
> XFS) both ownership models might make sense depending on the file
> system, although I think just giving it to the application is going
> to be the only thing we'll see for a while.  Maybe we need a way
> to query if the application can use the app tag? 

tag_size currently indicates the size of the app tag available to the
application. I.e. if ATO=1, tag_size is 2. And if ATO=0, tag_size is 0.

To properly support the NVMe extensions I guess we'll have to have
fields indicating the actual size of the reference and storage tags.

-- 
Martin K. Petersen	Oracle Linux Engineering