Re: Feature control on PV devices

[Joao Martins <joao.m.martins@oracle.com>]

On 09/18/2017 08:59 PM, Konrad Rzeszutek Wilk wrote:
> On Thu, Sep 14, 2017 at 05:08:18PM +0100, Joao Martins wrote:
>> [ Realized that I didn't CC the maintainers,
>>   so doing that now, +Linux folks +PV interfaces czar
>>   Sorry for the noise! ]
>>
>> On 09/08/2017 09:49 AM, Joao Martins wrote:
>>> [Forgot two important details regarding Xenbus states]
>>> On 09/07/2017 05:53 PM, Joao Martins wrote:
>>>> Hey!
>>>>
>>>> We wanted to brought up this small proposal regarding the lack of
>>>> parameterization on PV devices on Xen.
>>>>
>>>> Currently users don't have a way for enforce and control what
>>>> features/queues/etc the backend provides. So far there's only global parameters
>>>> on backends, and specs do not mention anything in this regard.
> 
> How would this scale with say FreeBSD backends?
>
This is per-device parameter configuration support, based on xenstore entries.
All backend needs to understand is that the request/XXX xenstore entries and
superseed whatever global defaults were defined by backend (after validation).
So what I am proposing here makes no OS assumptions and should work for FreeBSD
or any other.

> And I am assuming you are
> also thinking about device driver backends - where you can't easily
> get access to the backend and change the SysFS parameters (if they have
> it all)?
> 
Yeah - Provided that the xenstore entries will be created with permissions for
toolstack domain and the backend domain then backends other than Dom0 should
work too. Note that this is device setup (e.g. domain create time), i.e. the
configuration of what the frontend is allowed to see/use.

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