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

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Date:   Fri, 5 Jun 2020 18:39:15 +0300
From:   "Paraschiv, Andra-Irina" <andraprs@...zon.com>
To:     Stefan Hajnoczi <stefanha@...il.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 05/06/2020 11:15, Stefan Hajnoczi wrote:
> 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.

Agree, as we achieve the ultimate goal of having a stable interface, 
open for extensions without breaking changes.

Thanks,
Andra



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