Re: [dpdk-dev] [RFC 0/4] SocketPair Broker support for vhost and virtio-user.

[Ilya Maximets <i.maximets@ovn.org>]

On 3/25/21 10:35 AM, Stefan Hajnoczi wrote:
> On Wed, Mar 24, 2021 at 02:11:31PM +0100, Ilya Maximets wrote:
>> On 3/24/21 1:05 PM, Stefan Hajnoczi wrote:
>>> On Tue, Mar 23, 2021 at 04:54:57PM -0400, Billy McFall wrote:
>>>> On Tue, Mar 23, 2021 at 3:52 PM Ilya Maximets <i.maximets@ovn.org> wrote:
>>>>> On 3/23/21 6:57 PM, Adrian Moreno wrote:
>>>>>> On 3/19/21 6:21 PM, Stefan Hajnoczi wrote:
>>>>>>> On Fri, Mar 19, 2021 at 04:29:21PM +0100, Ilya Maximets wrote:
>>>>>>>> On 3/19/21 3:05 PM, Stefan Hajnoczi wrote:
>>>>>>>>> On Thu, Mar 18, 2021 at 08:47:12PM +0100, Ilya Maximets wrote:
>>>>>>>>>> On 3/18/21 6:52 PM, Stefan Hajnoczi wrote:
>>>>>>>>>>> On Wed, Mar 17, 2021 at 09:25:26PM +0100, Ilya Maximets wrote:
>> - How to get this fd again after the OVS restart?  CNI will not be invoked
>>   at this point to pass a new fd.
>>
>> - If application will close the connection for any reason (restart, some
>>   reconfiguration internal to the application) and OVS will be re-started
>>   at the same time, abstract socket will be gone.  Need a persistent daemon
>>   to hold it.
> 
> I remembered that these two points can be solved by sd_notify(3)
> FDSTORE=1. This requires that OVS runs as a systemd service. Not sure if
> this is the case (at least in the CNI use case)?
> 
> https://www.freedesktop.org/software/systemd/man/sd_notify.html

IIUC, these file descriptors only passed on the restart of the service,
so port-del + port-add scenario is not covered (and this is a very
common usecase, users are implementing some configuration changes this
way and also this is internally possible scenario, e.g. this sequence
will be triggered internally to change the OpenFlow port number).
port-del will release all the resources including the listening socket.
Keeping the fd for later use is not an option, because OVS will not know
if this port will be added back or not and fds is a limited resource.

It's also unclear how to map these file descriptors to particular ports
they belong to after restart.

OVS could run as a system pod or as a systemd service.  It differs from
one setup to another.  So it might not be controlled by systemd.

Also, it behaves as an old-style daemon, so it closes all the file
descriptors, forkes and so on.  This might be adjusted, though, with
some rework of the deamonization procedure.

On the side note, it maybe interesting to allow user application to
create a socket and pass a pollable file descriptor directly to
rte_vhost_driver_register() instead of a socket path.  This way
the user application may choose to use an abstract socket or a file
socket or any other future type of socket connections.  This will
also allow user application to store these sockets somewhere, or
receive them from systemd/init/other management software.

Best regards, Ilya Maximets.