linux-kernel - Re: [virtio-dev] Re: [RFC PATCH 1/1] virtio: write back features before verify

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Message-ID: <87r1cz2a76.fsf@redhat.com>
Date:   Tue, 05 Oct 2021 09:38:05 +0200
From:   Cornelia Huck <cohuck@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     Halil Pasic <pasic@...ux.ibm.com>,
        Jason Wang <jasowang@...hat.com>,
        Xie Yongji <xieyongji@...edance.com>,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, markver@...ibm.com,
        Christian Borntraeger <borntraeger@...ibm.com>,
        linux-s390@...r.kernel.org, virtio-dev@...ts.oasis-open.org
Subject: Re: [virtio-dev] Re: [RFC PATCH 1/1] virtio: write back features
 before verify

On Mon, Oct 04 2021, "Michael S. Tsirkin" <mst@...hat.com> wrote:

> On Mon, Oct 04, 2021 at 05:45:06PM +0200, Cornelia Huck wrote:
>> On Mon, Oct 04 2021, "Michael S. Tsirkin" <mst@...hat.com> wrote:
>> 
>> > On Mon, Oct 04, 2021 at 04:27:23PM +0200, Cornelia Huck wrote:
>> >> On Mon, Oct 04 2021, "Michael S. Tsirkin" <mst@...hat.com> wrote:
>> >> 
>> >> > Do we want to also add explanation that features can be
>> >> > changed until FEATURES_OK?
>> >> 
>> >> I always considered that to be implict, as feature negotiation is not
>> >> over until we have FEATURES_OK. Not sure whether we need an extra note.
>> >
>> > Well Halil here says once you set a feature bit you can't clear it.
>> > So maybe not ...
>> 
>> Ok, so what about something like
>> 
>> "If FEATURES_OK is not set, the driver MAY change the set of features it
>> accepts."
>> 
>> in the device initialization section?
>
> Maybe "as long as". However Halil implied that some features are not
> turned off properly if that happens. Halil could you pls provide
> some examples?

Yes, "as long as" sounds better.