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

[Jacob Gorm Hansen <jacobg@xxxxxxx>]

Anthony Liguori wrote:
> Jacob Gorm Hansen wrote:
>
> > 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).
>
> For just using notify, it's quite simply.  The control channels are 
> complicated because of the ring queue stuff.  If you were implementing 
> this as a virtual device in vm-tools (of course, I'm not bias ;-)), all 
> you would do is open /dev/evtchn and add that to the set of listener fds 
> (see the console device for an example of this).
> You would also need to allocate a port for notifications (vmm_alloc_port 
> in vm-tools or xc_evtchn_bind_interdomain otherwise).  The easiest thing 
> to do would be to use a well known endpoint (anything above 10 should be 
> relatively safe for now although you'll probably need to negotiate it in 
> the future).

Right now, in my domU driver I have:

    gfx_irq = bind_evtchn_to_irq(117);
    printk("got irq %d\n", gfx_irq);

    request_irq(gfx_irq, gfx_interrupt, SA_SAMPLE_RANDOM, "gfx", 0);

/which should get me interrupts when channel 117 gets notified, right?

> When you get a read event on /dev/evtchn, all you do is read a 2 byte 
> value from it.  This will be the port the event happened on.  You'll 
> also have to unmask the event by writing that same value back to the 
> device.
> > Can I setup my own event channel in the guest, and still access it 
> > using /dev/evtchn in dom0?
Hmm from looking at the code in drivers/xen/evtchn/evtchn.c, it seems if 
I write to this device, I can unmask local event channels, but there is 
no notion of a target domain.
If I want to notify eventchannel #117 in, say, domain 5, how can I do 
that from dom0 using /dev/xen/evtchn?
Thanks,
Jacob


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