Re: [PATCH v3 2/3] nvme: Pass pointers, not dma addresses, to nvme_get/set_features()

[Jens Axboe]

On 09/16/2016 09:13 AM, Andy Lutomirski wrote:
> On Sep 16, 2016 1:41 AM, "Christoph Hellwig" <hch@xxxxxx> wrote:
> > On Thu, Sep 15, 2016 at 10:24:20PM -0700, Andy Lutomirski wrote:
> > > Any user I can imagine that needs a buffer at all will want to pass
> > > a pointer directly.  There are no currently callers that use
> > > buffers, so this change is painless, and it will make it much easier
> > > to start using features that use buffers (e.g. APST).
> > >
> > > Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
> > > ---
> >
> > Looks good mostly good, but a nitpick below:
> >
> > > +     /*
> > > +      * Casting buffer to void* is safe here: __nvme_submit_sync_cmd knows
> > > +      * that we're writing because it decodes the opcode.
> > > +      */
> > > +     ret = __nvme_submit_sync_cmd(dev->admin_q, &c, &cqe,
> > > +                     (void *)buffer, buflen, 0, NVME_QID_ANY, 0, 0);
> >
> > Cant we just drop the const annotation to avoid these casts?
>
> Then we'd have nvme_set_feature() taking a non-const pointer, which
> would seem a little bit silly to me and might require the same cast
> somewhere else down the road.

That'd still be a lot cleaner than the cast, which needs a comment to
explain why it's supposedly safe. Just drop the const, imho.

--
Jens Axboe