[LSF/MM/BPF BOF] Userspace command abouts

[Sagi Grimberg]

>>>> I did not understand what is the relationship between aborts and CDL.
>>>> Sounds to me that this would tie in to something like Time Limited Error
>>>> Recovery (TLER) and LR bit set based on ioprio?
>>>>
>>>> I am unclear where do aborts come into play here.
>>>
>>> CDL: Command Duration Limits
>>>
>>> One use case is reading from storage for audio visual output.
>>> An application only wants to wait so long (e.g. one or two frames
>>> on the video output) before it wants to forget about the current
>>> read (i.e. "abort" it) and move onto the next read. An alert viewer
>>> might notice a momentary freeze frame.
>>>
>>> The SCSI CDL mechanism uses the DL0, DL1 and DL2 bits in the READ(16,32)
>>> commands. CDL also depends on the CDLP and RWCDLP fields in the
>>> REPORT SUPPORTED OPERATION CODES command and one of the CDL
>>> mode pages. So there may be some additional "wiring" needed in the
>>> SCSI subsystem.
>>
>> I still don't understand where issuing aborts from userspace come into
>> play here...
> 
> The only connection is that aborts are obsolete and unnecessary if
> you have a working CDL implementation.

OK, that makes sense. Indeed I *think* that nvme can support CDL and if
this is useful for userspace then this is an interesting path to take.