[QUESTION] About virtio and eventloop

[zhukeqian]

Hi all maintainers and community friends,

 

Recently I am reviewing and learning the virtio and eventloop implementation of latest QEMU,

and now I have a questions for help:

 

In general, the IO requests of virtio is popped in iothread/mainloop and may submitted to “async IO

Engine”  (io_uring/linux aio/threadpool). Once the IO operation is done, the “async IO engine” will send notification

to iothread/mainloop through evenfd or bottomhalf, and the completion action for the IO request (add used ring and

notify guest) is done in iothread/mainloop.

 

And let’s look at the “deactive” procedure of virtio-pci devices (when guest write 0 to  device status or system

triggered reset), the basic requirement is that device should stop handling IO requests and accessing virtqueue before

returning back to guest, as the guest may destroy virqueue  once deactivation is done.

 

QEMU invokes stop_ioeventfd() callback to perform above actions. It unregisters ioeventfd from eventloop and KVM,

1. but I can’t find code that ensuring IO operations in “async IO engine” are done.  
2. And if IO operation is blocked, is vCPU thread will blocked when do deactivate?

 

It’s great that if anyone can help!

 

Thanks,                                                                                  

Keqian