On 3/19/21 5:11 PM, Ilya Maximets wrote:

On 3/19/21 3:39 PM, Stefan Hajnoczi wrote:

quoted

Hi Ilya,
By the way, it's not clear to me why dpdkvhostuser is deprecated. If OVS
is restarted then existing vhost-user connections drop with an error but
QEMU could attempt to reconnect to the UNIX domain socket which the new
OVS instance will set up.

Why is it impossible to reconnect when OVS owns the listen socket?

Well, AFAIK, qemu reconnects client connections only:

    ``reconnect`` sets the timeout for reconnecting on non-server
    sockets when the remote end goes away. qemu will delay this many
    seconds and then attempt to reconnect. Zero disables reconnecting,
    and is the default.

I'm not sure about exact reason.  It was historically this way.
For me it doesn't make much sense.  I mean, your right that it's
just a socket, so it should not matter who listens and who connects.
If reconnection is possible in one direction, it should be possible
in the opposite direction too.

Sorry, my thought slipped. :)  Yes, QEMU supports re-connection
for client sockets.  So, in theory, dpdkvhostuser ports should work
after re-connection.  And that would be nice.  I don't remember
right now why this doesn't work...  Maybe vhost-user parts in QEMU
doesn't handle this case.  Need to dig some more into that and refresh
my memory.  It was so long ago...

Maxime, do you remember?

dpdkvhostuser was deprecated just to scare users and force them to
migrate to dpdkvhostuserclient and avoid constant bug reports like:

  "OVS service restarted and network is lost now".

BTW, virtio-user ports in DPDK doesn't support re-connection in client
mode too.

This is still true, though.  virtio-user in client mode doesn't reconnect.

BTW2, with SocketPair Broker it might be cheaper to implement server
reconnection in QEMU because all connections in these case are client
connections, i.e. both ends will connect() to a broker.

Bets regards, Ilya Maximets.