Re: [PATCH 1/4] nvdimm: Add wrapper for IOCTL pass thru.

[Linda Knippers]

On 11/10/2015 3:27 PM, Dan Williams wrote:
> On Tue, Nov 10, 2015 at 11:49 AM, Jerry Hoemann <jerry.hoemann@xxxxxxx> wrote:
> > On Tue, Nov 10, 2015 at 12:51:59PM -0500, Jeff Moyer wrote:
> > > Jerry Hoemann <jerry.hoemann@xxxxxxx> writes:
> > >
> > > > Add IOCTL type 'P' to denote NVDIMM_TYPE_PASSTHRU.
> > >
> > > Can't you just make passthrough a separate command?  If you actually add
> >
> > There are multiple conflicting NVDIMM _DSM running around, they
> > are "device specific".  So, we should plan in general and not just
> > for the example DSM that Intel added support for.  These DSM have
> > over lapping and incompatible function ids.
> >
> > The Intel example is an example,  not standard. They are free to
> > change it at will. So, we can't be certain there won't be a
> > conflict some time in the future if we try to use their number space.
> >
> > I'm trying to create a generic pass thru that any vendors can use.  Putting
> > this in the Intel function number space doesn't make a lot of sense to me.
>
> It isn't the "Intel" function number space.  The fact that they
> currently align is just a happy accident.

It's not really a happy accident. Your commit message says it
was derived from the Intel spec 'for convenience', which I think is convenient
for anything that implements that spec.

We've discussed ways of supporting different command sets with you
and determined that this pass-through mechanism was a good approach
because it allows multiple different command sets to be support in
a generic way.  Blending the two flavors (generic pass through and explicit
function definitions) is confusing to me.

> The kernel is free to break
> the 1:1 ioctl number to DSM function number relationship, and I think
> it would make the implementation cleaner in this case.

To me it's less clean and even for your own example spec, less
convenient if Intel ever updates that spec.

-- ljk
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