Re: [PATCH] xen/evtchn: Add design for static event channel signaling for domUs..

[David Vrabel <dvrabel@xxxxxxxxxx>]

On 23/03/2022 15:43, Rahul Singh wrote:
> in dom0less system. This patch introduce the new feature to support the
> signaling between two domUs in dom0less system.
>
> Signed-off-by: Rahul Singh <rahul.singh@xxxxxxx>
> ---
>   docs/designs/dom0less-evtchn.md | 96 +++++++++++++++++++++++++++++++++
>   1 file changed, 96 insertions(+)
>   create mode 100644 docs/designs/dom0less-evtchn.md
>
> diff --git a/docs/designs/dom0less-evtchn.md b/docs/designs/dom0less-evtchn.md
> new file mode 100644
> index 0000000000..6a1b7e8c22
> --- /dev/null
> +++ b/docs/designs/dom0less-evtchn.md
> @@ -0,0 +1,96 @@
> +# Signaling support between two domUs on dom0less system
> +
> +## Current state: Draft version
> +
> +## Proposer(s): Rahul Singh, Bertrand Marquis
> +
> +## Problem Statement:
> +
> +The goal of this work is to define a simple signaling system between Xen guests
> +in dom0less systems.
> +
> +In dom0less system, we cannot make use of xenbus and xenstore that are used in
> +normal systems with dynamic VMs to communicate between domains by providing a
> +bus abstraction for paravirtualized drivers.
> +
> +One possible solution to implement the signaling system between domUs is based
> +on event channels.
This problem statement could do with some example use cases that are 
usefully solved by this proposed solution.
"We don't have xenstore so can't set up shared rings, but here's a 
replacement comms mechanism that can do a single bit." Doesn't seem very 
compelling to me.
> +    chosen {
> +        ....
> +
> +        domU1: domU1 {
> +            ......
> +        };
> +
> +        domU2: domU2 {
> +            ......
> +        };
> +
> +        evtchn@1 {
> +            compatible = "xen,evtchn";
> +            xen,evtchn = <0xa &domU1 0xb &domU2>;
> +        };
> +
> +        evtchn@2 {
> +            compatible = "xen,evtchn";
> +            xen,evtchn = <0xc &domU1 0xd &domU2>;
> +        };
How is the domain supposed to know what these event channels are for?

I'm not that familiar with device tree. Is it possible to give these 
entries name?
David