Re: [virtio-dev] [PATCH v5 08/10] vhost-user: remove the extra PCI capabilities

[Stefan Hajnoczi <stefanha@redhat.com>]

On Mon, May 18, 2020 at 11:37:19PM +0300, Nikos Dragazis wrote:
> -Additional resources are configured on the virtio PCI transport by the following \field{struct virtio_pci_cap.cfg_type} values:
> +\subsubsection{Doorbell layout}\label{sec:Device Types / Vhost-user Device Backend / Additional Device Resources / Doorbell layout}
>  
> -\begin{lstlisting}
> -#define VIRTIO_PCI_CAP_DOORBELL_CFG 6
> -#define VIRTIO_PCI_CAP_NOTIFICATION_CFG 7
> -#define VIRTIO_PCI_CAP_SHARED_MEMORY_CFG 8
> -\end{lstlisting}
> +The device MUST reserve 2N+1 virtqueue indices that can be used by the driver to
> +send doorbell notifications. The driver can use these indices to send doorbell
> +notifications in the same way that it sends available buffer notifications
> +\ref{sec:Basic Facilities of a Virtio Device / Notifications} for a virtqueue.

Notifications and doorbells should be first-class VIRTIO device model
concepts, like Shared Memory resources. It should not be necessary to
reserve dummy virtqueues (a hack for getting MSI-X vectors and doorbell
registers).

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