[ovs-discuss] detecting supported port types and enabling dpdk datapaths in OpenStack

[Ben Pfaff]

On Wed, Jul 23, 2014 at 03:46:24PM +0000, Mooney, Sean K wrote:
> 1.            The command line of the ovs-vSwitchd process could be stored in the ovsdb. (least preferable option,  but smallest change)
> 2.            The datapath type of the DPDK build could be changed to NETDEV-DPDK (better, but not optimal)
> 3.            The bridge table in the ovsdb  could be extended with a supported_port_types field.

Of those options, #3 seems the best to me too.

It is easy for Open vSwitch to internally enumerate all of the types
of netdevs it supports (just call netdev_enumerate_types()).  It's
more difficult to figure out which types of datapaths support
particular netdev types, since netdevs aren't tied directly to
datapaths.  It might be appropriate to couple netdevs more closely to
datapaths, I would not want to just have each datapath provide a list
(e.g. in the form of a set of strings), because that could easily get
out of sync.

When other factors don't rule it out, it's ideal to probe for a
feature by trying it to see whether it works, because that isn't
sensitive to false positives or false negatives due to incorrect
capabilities announced by the software being tested.  (This is the
same philosophy as Autoconf.)  Have you considered using a feature
probe, by simply trying to use the feature that you want to use from
OpenStack?