[LSF/MM/BPF BOF] Userspace command abouts

[Keith Busch]

On Wed, Feb 22, 2023 at 04:37:51PM +0200, Sagi Grimberg wrote:
> 
> > > 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.