On Wed, 2017-03-22 at 19:19 +0100, Christoph Hellwig wrote: > On Tue, Mar 21, 2017 at 02:59:01PM -0400, Tejun Heo wrote: > > I do like the fact that this is a lot simpler than the previous > > implementation but am not quite sure we want to deviate > > significantly from what we do for other commands (command > > translation). Is it because fixing the existing implementation > > would involve invaisve changes including memory allocations? > > The current implementation already has the issue of that it does > corrupt user data reliably if the using SG_IO for WRITE SAME > commands. That does need fixing. > Doing ranges using translation would turn into a nightmare because > ATA TRIM ranges are 16 bits long while SCSI UNAMP ranges are 32-bit, > so we effectively can't translated them without introducing a > non-standard hook between libata and scsi to communicate that > limit. Why can't we do what the t10 sat document recommends: if the ATA device doesn't support the XL version (32 bit ranges) then translate unmap to multiple non-XL commands? I don't necessarily object to the vendor specific 1<->1 approach, it's just it won't fix the problem you cited above (SG_IO WRITE SAME), its just that now we error the command, which may cause some surprise. I also wonder if we couldn't simply do an ATA_16 TRIM if we're already going to all the trouble of recognising ATA devices in the sd discard path? James > And once we're down that path we might as well just do the > right thing directly.
