linux-kernel - Re: [PATCH v3 2/3] nvme: Pass pointers, not dma addresses, to nvme_get/set

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Date:   Fri, 16 Sep 2016 08:13:31 -0700
From:   Andy Lutomirski <luto@...capital.net>
To:     Christoph Hellwig <hch@....de>
Cc:     linux-nvme@...ts.infradead.org,
        J Freyensee <james_p_freyensee@...ux.intel.com>,
        Keith Busch <keith.busch@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Jens Axboe <axboe@...com>
Subject: Re: [PATCH v3 2/3] nvme: Pass pointers, not dma addresses, to nvme_get/set_features()

On Sep 16, 2016 1:41 AM, "Christoph Hellwig" <hch@....de> 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@...nel.org>
> > ---
>
> 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.