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Date:   Fri, 5 Jun 2020 09:15:03 +0100
From:   Stefan Hajnoczi <stefanha@gmail.com>
To:     "Paraschiv, Andra-Irina" <andraprs@amazon.com>
Cc:     Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        linux-kernel@vger.kernel.org,
        Anthony Liguori <aliguori@amazon.com>,
        Colm MacCarthaigh <colmmacc@amazon.com>,
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        David Woodhouse <dwmw@amazon.co.uk>,
        Frank van der Linden <fllinden@amazon.com>,
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        Martin Pohlack <mpohlack@amazon.de>,
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        Paolo Bonzini <pbonzini@redhat.com>,
        Balbir Singh <sblbir@amazon.com>,
        Stefano Garzarella <sgarzare@redhat.com>,
        Stefan Hajnoczi <stefanha@redhat.com>,
        Stewart Smith <trawets@amazon.com>,
        Uwe Dannowski <uwed@amazon.de>, kvm@vger.kernel.org,
        ne-devel-upstream@amazon.com
Subject: Re: [PATCH v3 01/18] nitro_enclaves: Add ioctl interface definition
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On Mon, Jun 01, 2020 at 10:20:18AM +0300, Paraschiv, Andra-Irina wrote:
>=20
>=20
> On 01/06/2020 06:02, Benjamin Herrenschmidt wrote:
> > On Wed, 2020-05-27 at 09:49 +0100, Stefan Hajnoczi wrote:
> > > What about feature bits or a API version number field? If you add
> > > features to the NE driver, how will userspace detect them?
> > >=20
> > > Even if you intend to always compile userspace against the exact kern=
el
> > > headers that the program will run on, it can still be useful to have =
an
> > > API version for informational purposes and to easily prevent user
> > > errors (running a new userspace binary on an old kernel where the API=
 is
> > > different).
> > >=20
> > > Finally, reserved struct fields may come in handy in the future. That
> > > way userspace and the kernel don't need to explicitly handle multiple
> > > struct sizes.
> > Beware, Greg might disagree :)
> >=20
> > That said, yes, at least a way to query the API version would be
> > useful.
>=20
> I see there are several thoughts with regard to extensions possibilities.=
 :)
>=20
> I added an ioctl for getting the API version, we have now a way to query
> that info. Also, I updated the sample in this patch series to check for t=
he
> API version.

Great. The ideas are orthogonal and not all of them need to be used
together. As long as their is a way of extending the API cleanly in the
future then extensions can be made without breaking userspace.

Stefan

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