On 2020/06/17 1:13, Javier González wrote: > On 16.06.2020 09:07, Keith Busch wrote: >> On Tue, Jun 16, 2020 at 05:55:26PM +0200, Javier González wrote: >>> On 16.06.2020 08:48, Keith Busch wrote: >>>> On Tue, Jun 16, 2020 at 05:02:17PM +0200, Javier González wrote: >>>>> This depends very much on how the FS / application is managing >>>>> stripping. At the moment our main use case is enabling user-space >>>>> applications submitting I/Os to raw ZNS devices through the kernel. >>>>> >>>>> Can we enable this use case to start with? >>>> >>>> I think this already provides that. You can set the nsid value to >>>> whatever you want in the passthrough interface, so a namespace block >>>> device is not required to issue I/O to a ZNS namespace from user space. >>> >>> Mmmmm. Problem now is that the check on the nvme driver prevents the ZNS >>> namespace from being initialized. Am I missing something? >> >> Hm, okay, it may not work for you. We need the driver to create at least >> one namespace so that we have tags and request_queue. If you have that, >> you can issue IO to any other attached namespace through the passthrough >> interface, but we can't assume there is an available namespace. > > That makes sense for now. > > The next step for us is to enable a passthrough on uring, making sure > that I/Os do not split. Passthrough as in "application issues directly NVMe commands" like for SG_IO with SCSI ? Or do you mean raw block device file accesses by the application, meaning that the IO goes through the block IO stack as opposed to directly going to the driver ? For the latter case, I do not think it is possible to guarantee that an IO will not get split unless we are talking about single page IOs (e.g. 4K on X86). See a somewhat similar request here and comments about it. https://www.spinics.net/lists/linux-block/msg55079.html > > Does this make sense to you? > > Thanks, > Javier > -- Damien Le Moal Western Digital Research
