Re: [PATCH v15 7/9] nvmet-passthru: Add passthru code to process commands

[Sagi Grimberg]

> > > Thanks for the review Christoph. I think I should be able to make all
> > > the requested changes in the next week or two.
> > >
> > > On 2020-07-20 1:35 p.m., Sagi Grimberg wrote:
> > > > > I'm still not so happy about having to look up the namespace and still
> > > > > wonder if we should generalize the connect_q to a passthrough_q. But
> > > > > I guess we can do that later and then reduce some of the exports here..
> > > >
> > > > That is a neat idea! should be easy to do (and we can then lose the host
> > > > xarray stuff). I don't mind having it on a later patch, but it should be
> > > > easy enough to do even before...
> > >
> > > I sort of follow this. I can try to work something up but it will
> > > probably take me a few iterations to get it to where you want it. So,
> > > roughly, we'd create a passthrough_q in core with the controller's IO
> > > tagset and then cleanup the fabrics hosts to use that instead of each
> > > independently creating their connect_q?
> > >
> > > Though, I don't understand how this relates to the host xarray stuff
> > > that Sagi mentioned...
> >
> > passthru commands are in essence REQ_OP_DRV_IN/REQ_OP_DRV_OUT, which
> > means that the driver shouldn't need the ns at all. So if you have a
> > dedicated request queue (mapped to the I/O tagset), you don't need the
> > ns->queue and we can lose the ns lookup altogether.
> >
> > The only part is to check the effects, but that can probably be handled
> > when we setup the passthru controller or something...
>
> Yes, I implemented the passthru_q (which was quite simple).

Nice..

> But I'm not
> sure how we are supposed to call nvme_command_effects() correctly
> without the ns. You can't possibly do that during setup for every
> possible opcode on every namespace. And even if we do, we'll still need
> the same nvme_find_get_ns() and nvme_put_ns() exports and probably
> another xarray to lookup the information.
>
> Also, we pass the namespace's disk to in order to get proper block
> accounting for the underlying disk. (Which is pretty important for
> debugging). So we need to lookup the namespace for this too.
>
> Unless there are some other ideas to solve these issues, I don't think
> this change will gain us anything.

Let's defer it to a followup set than.