allow using tap device on netdev enabled host

[norman shen]

hello, after reading the code, it seems nova-compute can only use vhostuser mode if netdev is enabled on ovs bridge. an internal use case requires us to allow using tap device as well as vhostuser device on the same host. Do this sound like a valid use case?

[Akihiro Motoki (amotoki)]

Could you share more detail information on why the tap device is needed?
More information would help us understand the background.

[Rodolfo Alonso (rodolfo-alonso-hernandez)]

Hello:

I assume you are talking about OVS ML2 plugin.

All traffic goes through the integration bridge (usually "br-int"). The datapath type is defined at bridge level. If this bridge datapath type is "netdev", only "dpdkvhostuser" or "dpdkvhostuserclient" ports can be attached. If the datapath type is "system", only normal tap ports can be created and attached.

You cannot mix both types.

Regards.

[norman shen (jshen28)]

hi all, thank you very much for the replies. the background is that vhostuser typed port requires hugepages to be used, so the idea behind this request is to potentially save some memory by using tap devices.

actually tap device could still be used even for netdev data_path but of course there will be some penalties on performance.