Re: [Qemu-devel] question about qemu IO process

[Stefan Hajnoczi]

On Thu, Dec 15, 2016 at 02:50:41PM +0800, address@hidden wrote:
> I recently try to figure out the the whole IO process in qemu, I have traced 
> most parts of this process, but I'm still confused about how guest OS notify 
> qemu to handle virtqueue
> I traced to virtio_queue_host_notifier_read -> event_notifier_test_and_clear, 
> and qemu will read e->rfd, so I assumed that some part of code will write to 
> this descriptor, to notify qemu
> Unfortunatelly, I have set some breakpoints but noting catched yet.
> Could someone point it out for me which code write to this descriptor? Or 
> show me the web link about this design?

"The KVM kernel module has a feature known as ioeventfd for taking an
eventfd and hooking it up to a particular guest I/O exit. QEMU userspace
registers an ioeventfd for the VIRTIO_PCI_QUEUE_NOTIFY hardware register
access which kicks the virtqueue."

From http://blog.vmsplice.net/2011/09/qemu-internals-vhost-architecture.html
(careful the rest of the post is about vhost, not QEMU)

http://blog.allenx.org/2015/07/05/kvm-irqfd-and-ioeventfd

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