Re: [Qemu-devel] [PATCH 3/4] net/virtio: add failover support

[Eduardo Habkost]

On Fri, May 31, 2019 at 05:05:26PM -0400, Michael S. Tsirkin wrote:
> On Fri, May 31, 2019 at 02:29:33PM -0600, Alex Williamson wrote:
> > I don't know what this frontend/backend rework would
> > look like for vfio-pci, but it seems non-trivial for this one use case
> > and I don't see that it adds any value outside of this use case,
> > perhaps quite the opposite, it's an overly complicated interface for
> > the majority of use cases so we either move to a more complicated
> > interface or maintain both.  Poor choices either way.
> 
> Well put Alex this is what I meant when I said it's a useless
> interface. I meant it only has a single use.

I might agree if the code needed to hide the VFIO device from the
guest while keeping resources open (so it can be re-added if
migration fails) is demonstrably simpler than the code that would
be necessary to separate the device backend from the frontend.

But I couldn't find the code that does that in this series.  Is
this already implemented?

All I see is a qdev_unplug() call (which will close host
resources) and a qdev_device_add() call (which will reopen the
host device).

-- 
Eduardo