Re: Inter VM Communication

[Avi Kivity <avi@redhat.com>]

Cam Macdonell wrote:
>> If you just want to share a page (or a bunch of memory), write a qemu 
>> PCI device model that exposes that page through a BAR.  The guests 
>> can then map the BAR and access the page.
>>
>> To share the page, use normal Linux memory sharing, such as shared 
>> memory segments or mapped files (possibly on /dev/shm).
>
> I've actually created a patch (and corresponding device driver) that 
> works this way based on Avi's suggestion of this approach before.  I'm 
> willing to release it of course, but it's in pretty rough form being 
> my first Qemu/KVM PCI device.  Avi (or anyone else), would you mind 
> having a quick look first before I release it to the list?

I'm of course willing to take a look, but I think you should post it 
directly to the list.  More eyes mean more comments, and on this list we 
usually see constructive criticism.

>
> I haven't implemented PCI interrupts yet, but would appreciate some 
> pointers on how to go about this.

Call qemu_set_irq(pci_dev->irq[0], 1) when you want your guest to take 
notice, and qemu_set_irq(pci_dev->irq[0], 0) when service is no longer 
necessary.

You'll also need to set pci_dev->config[PCI_INTERRUPT_PIN] to 1 to let 
the guest know you're using irq[0].

See virtio or rtl8139.c as examples.

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.