[PATCH 13/17] nvme: allow user passthrough commands to poll

[Kanchan Joshi]

On Tue, Mar 8, 2022 at 10:39 PM Keith Busch <kbusch at kernel.org> wrote:
>
> On Tue, Mar 08, 2022 at 08:51:01PM +0530, Kanchan Joshi wrote:
> >       if (copy_from_user(&io, uio, sizeof(io)))
> >               return -EFAULT;
> > -     if (io.flags)
> > -             return -EINVAL;
> > +     if (io.flags & NVME_HIPRI)
> > +             rq_flags |= REQ_POLLED;
>
> I'm pretty sure we can repurpose this previously reserved field for this
> kind of special handling without an issue now, but we should continue
> returning EINVAL if any unknown flags are set. I have no idea what, if
> any, new flags may be defined later, so we shouldn't let a future
> application think an older driver honored something we are not handling.

Would it be better if we don't try to pass NVME_HIPRI by any means
(flags or rsvd1/rsvd2), and that means not enabling sync-polling and
killing this patch.
We have another flag "IO_URING_F_UCMD_POLLED" in ioucmd->flags, and we
can use that instead to enable only the async polling. What do you
think?