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

[Wei Wang <wei.w.wang@intel.com>]

On 01/24/2018 07:40 PM, Stefan Hajnoczi wrote:
> 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?

Is this an explicit qmp operation to make the master re-connect?

>
>> 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?

OK. I think that's not needed if the master can reconnect.

>
>> 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

Thanks. I haven't got time on this yet due to some more urgent things. 
I'll try.

Best,
Wei