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Re: [Xen-devel] To use xcs or not?

Anthony Liguori wrote:
Jacob Gorm Hansen wrote:

I am creating a graphics system where each VM draws into an OpenGL surface of a process running in dom0. I need to syncronize updates, ideally with the vertical blanking of the screen, but in the world of stupid PC hardware probably just with some refresh timer that my OpenGL process is tied to.

Neat, is this some sort of specialized application or are you implementing a virtual frame buffer?

This is a specialized app for a research project, and the way I store pixels means I will not be compatible with applications using the kernel frame buffer, at least not initially. Hopefully my approach will so much better that people will dump X and recode their toolkits to run on my stuff though ;-) It will probably be a little while before this is at a level where it is usable to anyone else than me, but right now I do have some cool demos running.

So when the screen has been redrawn, I need to wake up my domUs, and for this I wanted to use the ctrl_if mechanism. I borrowed some code from vm-shutdown in the (very nice) vm-tools package, setup a semaphore in the guest kernel, and for every screen update I send an XCS_REQUEST (only type that seems to do anything) up to the domU.

This is probably a little overkill. If all you need is notification, you probably just want to setup your own evtchn.

OK, I actually got the impression that using XCS was the easiest way around the problem, as you seem to need a lot of code for setting up your own channel (which I can copy-paste from somewhere I am sure).

Can I setup my own event channel in the guest, and still access it using /dev/evtchn in dom0?


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