Re: [Qemu-devel] [virtio-net] migration

[Stefan Hajnoczi]

On Fri, May 27, 2016 at 12:59:51PM +0000, Catalin Vasile wrote:
> What is the workflow for virtio-net devices when migrating the VM it belongs 
> to?
> From what I understand so far the stop() primitives in qemu are called for 
> virtio_net and vhost_net which makes the virtqueue reset such that it seems 
> the queues are completely empty.
> How does the guest know that the jobs he sent on the virtqueue were discarded 
> so that he can retry or release resources that were used for managing those 
> jobs/packets?

No, virtqueues stay as-is across migration.  vring state (e.g.
last_avail_idx) is migrated so that the new QEMU can pick up where the
old one left off.

See hw/virtio/virtio.c load/save code to learn more.

Stefan

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