Re: [PATCH v2] content: clarify feature negotiation terminology and init sequence

[Stefan Hajnoczi <stefanha@redhat.com>]

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On Thu, Apr 23, 2026 at 06:24:12PM -0400, Michael S. Tsirkin wrote:
> Make several clarifications to the init sequence documentation:
> 
> The Linux virtio core (drivers/virtio/virtio.c) initializes devices
> as follows:
>   1. Intersect driver and device feature bits
>   2. finalize_features() - write accepted features to the device
>   3. drv->validate() - read config space, may clear feature bits
>      (e.g. virtio-net clears VIRTIO_NET_F_MTU if mtu < MIN_MTU,
>      balloon clears PAGE_POISON if guest does not init pages)
>   4. If validate changed any features, finalize_features() again
>   5. virtio_features_ok() - set FEATURES_OK, confirm with device
> 
> this allows the device to know which fields will be read:
> recommend this in the spec.
> 
> Legacy driver detection is specified using a mechanism that
> does not work on all transports. Make it clear that it's an
> example: what matters is that devices do detection in some way
> and are compatible with legacy drivers.
> 
> Define "negotiated" for features confirmed via FEATURES_OK.
> 
> "acknowledged" is used as a synonym for "accepted", but only in two
> places. Just use "accepted" consistently.
> 
> Spec describes multiple moving pieces then ends with "before accepting
> it" - vague, and is overloading "accept". Replace with a reference to
> FEATURES_OK.
> 
> Fixes: https://github.com/oasis-tcs/virtio-spec/issues/241
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> ---
> 
> changes:
> address review comments by Stefan
> 
>  content.tex | 28 +++++++++++++++++++++-------
>  1 file changed, 21 insertions(+), 7 deletions(-)

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

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