linux-kernel - Re: [PATCH v3 01/18] nitro_enclaves: Add ioctl interface definition

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Message-ID: <20200605081503.GA59410@stefanha-x1.localdomain>
Date:   Fri, 5 Jun 2020 09:15:03 +0100
From:   Stefan Hajnoczi <stefanha@...il.com>
To:     "Paraschiv, Andra-Irina" <andraprs@...zon.com>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        linux-kernel@...r.kernel.org,
        Anthony Liguori <aliguori@...zon.com>,
        Colm MacCarthaigh <colmmacc@...zon.com>,
        Bjoern Doebel <doebel@...zon.de>,
        David Woodhouse <dwmw@...zon.co.uk>,
        Frank van der Linden <fllinden@...zon.com>,
        Alexander Graf <graf@...zon.de>,
        Martin Pohlack <mpohlack@...zon.de>,
        Matt Wilson <msw@...zon.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Balbir Singh <sblbir@...zon.com>,
        Stefano Garzarella <sgarzare@...hat.com>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        Stewart Smith <trawets@...zon.com>,
        Uwe Dannowski <uwed@...zon.de>, kvm@...r.kernel.org,
        ne-devel-upstream@...zon.com
Subject: Re: [PATCH v3 01/18] nitro_enclaves: Add ioctl interface definition

On Mon, Jun 01, 2020 at 10:20:18AM +0300, Paraschiv, Andra-Irina wrote:
> 
> 
> 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?
> > > 
> > > Even if you intend to always compile userspace against the exact kernel
> > > 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).
> > > 
> > > 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 :)
> > 
> > That said, yes, at least a way to query the API version would be
> > useful.
> 
> I see there are several thoughts with regard to extensions possibilities. :)
> 
> 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 the
> 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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