Re: [Qemu-devel] [RFC 0/2] virtio-vhost-user: add virtio-vhost-user device

[Stefan Hajnoczi <stefanha@redhat.com>]

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On Tue, Jan 23, 2018 at 09:06:49PM +0800, Wei Wang wrote:
> On 01/23/2018 07:12 PM, Stefan Hajnoczi wrote:
> > On Mon, Jan 22, 2018 at 07:09:06PM +0800, Wei Wang wrote:
> > > On 01/19/2018 09:06 PM, Stefan Hajnoczi wrote:
> > > 
> > > 
> > >   - Suppose in the future there is also a kernel virtio-vhost-user driver as
> > > other PCI devices, can we unbind the kernel driver first, and then bind the
> > > device to the dpdk driver? A normal PCI device should be able to smoothly
> > > switch between the kernel driver and dpdk driver.
> > It depends what you mean by "smoothly switch".
> > 
> > If you mean whether it's possible to go from a kernel driver to
> > vfio-pci, then the answer is yes.
> > 
> > But if the kernel driver has an established vhost-user connection then
> > it will be closed.  This is the same as reconnecting with AF_UNIX
> > vhost-user.
> > 
> 
> Actually not only the case of switching to testpmd after kernel establishes
> the connection, but also for several runs of testpmd. That is, if we run
> testpmd, then exit testpmd. I think the second run of testpmd won't work.

The vhost-user master must reconnect and initialize again (SET_FEATURES,
SET_MEM_TABLE, etc).  Is your master reconnecting after the AF_UNIX
connection is closed?

> I'm thinking about caching the received master msgs in QEMU when
> virtio_vhost_user_parse_m2s().

Why is that necessary and how does QEMU know they are still up-to-date
when a new connection is made?

> Btw, I'm trying to run the code, but couldn't bind the virito-vhost-user
> device to vfio-pci (reports Unknown device), not sure if it is because the
> device type is "Unclassified device".

You need to use the modified usertools/dpdk-devbind.py from my patch
series inside the guest.  Please see:
https://dpdk.org/ml/archives/dev/2018-January/088177.html

Stefan

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