Re: [PATCH 5/8] xen/evtchn: don't close the static event channel.

[Julien Grall <julien@xxxxxxx>]

On 05/07/2022 14:28, Rahul Singh wrote:
> Hi Julien,
Hi Rahul,

> > On 28 Jun 2022, at 4:18 pm, Julien Grall <julien@xxxxxxx> wrote:
> > > a new driver in linux kernel, etc where right now we just need to introduce an 
> > > extra IOCTL in linux to support this feature.
> > I don't understand why would need a new driver, etc. Given that you are introducing a new 
> > IOCTL you could pass a flag to say "This is a static event channel so don't close 
> > it".
> I tried to implement other solutions to this issue. We can introduce a new event channel 
> state “ECS_STATIC” and set the
> event channel state to ECS_STATIC when Xen allocate and create the static event 
> channels.
From what you wrote, ECS_STATIC is just an interdomain behind but where 
you want Xen to prevent closing the port.
From Xen PoV, it is still not clear why this is a problem to let Linux 
closing such port. From the guest PoV, there are other way to pass this 
information (see below).
>  From guest OS we can check if the event channel is static (via 
> EVTCHNOP_status()  hypercall ), if the event channel is
> static don’t try to close the event channel. If guest OS try to close the static event 
> channel Xen will return error as static event channel can’t be closed.
Why do you need this? You already need a binding indicating which ports 
will be pre-allocated. So you could update your binding to pass a flag 
telling Linux "don't close it".
I have already proposed that before and I haven't seen any explanation 
why this is not a viable solution.
Cheers,

--
Julien Grall