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

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Date:   Mon, 01 Jun 2020 13:02:59 +1000
From:   Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:     Stefan Hajnoczi <stefanha@...il.com>,
        Andra Paraschiv <andraprs@...zon.com>
Cc:     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 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.

Cheers,
Ben.