Re: [PATCH v2] nvme: allow 64-bit results in passthru commands

[James Smart]

On 8/19/2019 7:49 AM, Keith Busch wrote:
> On Mon, Aug 19, 2019 at 12:06:23AM -0700, Marta Rybczynska wrote:
> > ----- On 16 Aug, 2019, at 15:16, Christoph Hellwig hch@xxxxxx wrote:
> > > Sorry for not replying to the earlier version, and thanks for doing
> > > this work.
> > >
> > > I wonder if instead of using our own structure we'd just use
> > > a full nvme SQE for the input and CQE for that output.  Even if we
> > > reserve a few fields that means we are ready for any newly used
> > > field (at least until the SQE/CQE sizes are expanded..).
> > We could do that, nvme_command and nvme_completion are already UAPI.
> > On the other hand that would mean not filling out certain fields like
> > command_id. Can do an approach like this.
> Well, we need to pass user space addresses and lengths, which isn't
> captured in struct nvme_command.
This is going to be fun. It's going to have to be a cooperative effort 
between app and transport. There will always need to be some parts of 
the SQE filled out by the transport like SGL, command type/subtype bits, 
as well as dealing with buffers as Keith states. Command ID is another 
of those fields.

-- james