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    SubjectRe: [PATCH 1/3] A device for zero-copy based on KVM virtio-net.
    On Wed, Apr 07, 2010 at 10:41:08AM +0800, Xin, Xiaohui wrote:
    > Michael,
    > >> Qemu needs a userspace write, is that a synchronous one or
    > >>asynchronous one?
    > >It's a synchronous non-blocking write.
    > Sorry, why the Qemu live migration needs the device have a userspace write?
    > how does the write operation work? And why a read operation is not cared here?
    > Thanks
    > Xiaohui

    Roughly, with ethernet bridges, moving a device from one location in
    the network to another makes forwarding tables incorrect (or incomplete),
    until outgoing traffic from the device causes these tables
    to be updated. Since there's no guarantee that guest
    will generate outgoing traffic, after migration qemu sends out several
    dummy packets itself.


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