[Qemu-devel] dataplane bug: fail to start VM with dataplane enable

[Dunrong Huang]

Hi,  Paolo && Stefan:

When I test the dataplane feature with git master, I find that VM will
hang if dataplane is enabled. But if I use qemu-1.4.0, VM can start
normally.

The command I boot QEMU is:
x86_64-softmmu/qemu-system-x86_64 -enable-kvm -m 1024 -smp 2 -drive
file=centos-6.4.raw,if=none,id=drive-virtio-disk,format=raw,cache=none,aio=native
-device 
virtio-blk-pci,config-wce=off,scsi=off,x-data-plane=on,drive=drive-virtio-disk,id=virtio-disk

git bisect implicates this bug was introduced by following commit:

commit 82959e8262df7da882d715f8a0cb4e8c7cd6e94b
Author: Paolo Bonzini <address@hidden>
Date:   Fri Feb 22 10:40:34 2013 +0100

    dataplane: remove EventPoll in favor of AioContext

    During the review of the dataplane code, the EventPoll API morphed itself
    (not concidentially) into something very very similar to an AioContext.
    Thus, it is trivial to convert virtio-blk-dataplane to use AioContext,
    and a first baby step towards letting dataplane talk directly to the
    QEMU block layer.

    The only interesting note is the value-copy of EventNotifiers.  At least
    in my opinion this is part of the EventNotifier API and is even portable
    to Windows.  Of course, in this case you should not close the notifier's
    underlying file descriptors or handle with event_notifier_cleanup.

    Signed-off-by: Paolo Bonzini <address@hidden>
    Signed-off-by: Stefan Hajnoczi <address@hidden>

I can provide more information if need.
-- 
Best Regards,

Dunrong Huang