Re: [Xen-devel] [RFC PATCH 4/6] vm_event: Use slotted channels for sync requests.

[Petre Ovidiu PIRCALABU <ppircalabu@xxxxxxxxxxxxxxx>]

On Thu, 2018-12-20 at 12:05 +0000, Paul Durrant wrote:
> > -----Original Message-----
> > 
> > The memory for the asynchronous ring and the synchronous channels
> > will
> > be allocated from domheap and mapped to the controlling domain
> > using the
> > foreignmemory_map_resource interface. Unlike the current
> > implementation,
> > the allocated pages are not part of the target DomU, so they will
> > not be
> > reclaimed when the vm_event domain is disabled.
> 
> Why re-invent the wheel here? The ioreq infrastructure already does
> pretty much everything you need AFAICT.
> 
>   Paul
> 

Hi Paul,

I'm still struggling to understand how the vm_event subsystem could be
integrated with an IOREQ server.

An IOREQ server shares with the emulator 2 pages, one for ioreqs and
one for buffered_ioreqs. For vm_event we need to share also one or more
pages for the async ring and a few pages for the slotted synchronous
vm_events.
So, to my understanding, your idea to use the ioreq infrastructure for
vm_events is basically to replace the custom signalling (event channels
+ ring / custom states) with ioreqs. Since the
vm_event_request/response structures are larger than 8 bytes, the
"data_is_ptr" flag should be used in conjunction with the addresses
(indexes) from the shared vm_event buffers. 

Is this the mechanism you had in mind?

Many thanks,
Petre

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