Re: To use xcs or not?

[Jacob Gorm Hansen <jacobg@diku.dk>]

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?

Thanks,
Jacob



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