FYI, I have absolutely no interest in supporting any userspace hooks in nvmet.
Don't think we are discussing adding anything specific to nvmet, a userspace backend will most likely sit behind a block device exported via nvmet (at least from my perspective). Although I do see issues with using the passthru interface...
If you want a userspace nvme implementation please use SPDK.
The original use-case did not include nvmet, I may have stirred the pot saying that we have nvmet loopback instead of a new kind of device with a new set of tools. I don't think that spdk meets even the original android use-case. Not touching nvmet is fine, it just eliminates some of the possible use-cases. Although personally I don't see a huge issue with adding yet another backend to nvmet...
