Re: [dpdk-dev] [PATCH v2] net/enic: add private API to set ingress VLAN rewrite mode

[Thomas Monjalon <thomas@monjalon.net>]

13/03/2019 22:11, John Daley (johndale):
> From: Thomas Monjalon <thomas@monjalon.net>
> > 13/03/2019 19:32, Ferruh Yigit:
> > > On 3/5/2019 7:11 AM, Hyong Youb Kim wrote:
> > > > The driver currently has a devarg to set the rewrite mode during
> > > > init. Some apps want to programatically set it after running
> > > > rte_eal_init() and finding that ports are VIC. Add a private
> > > > function to support such applications.
> > >
> > > It is not good idea to have PMD specific APIs (although we already have
> > some).
> > >
> > > Specific to this case, as far as I can see it is to pass a config
> > > value and do the action related to it, what would you think having a
> > > generic key/value set/get API in ethdev for this? Similar to rawdev
> > get_attr/set_attr [1]?
> > >
> > > My concern is it may turn into something like ioctl with many things
> > > pushed to it, and cause possible duplication ...
> > 
> > Yes, it is clearly ioctl style.
> > 
> > Please could you explain more what is the rewrite mode?
> > Does it apply to the port or the queue?
> > 
> It applies to a port. By default the Cisco VIC VLAN tags every packet on ingress even if they were untagged coming in on the wire. They are tagged with VLAN 0 or a VLAN id programmed into the NIC depending on the configuration. Its part of the original design, to maintain priority bits, ancient history.
> 
> Some apps don't like this (VPP) or take a slower path (OVS). Hyong added a ig-vlan-rewrite=untag devarg to disable this (leave untagged/default vlan packets untagged) during rte_eal_init and this is helpful for OVS, but VPP likes to set the rewrite mode after rte_eal_init() and finding the ports are VIC ports. So that is the reasoning behind the private API call.

It looks like an application will always set this flag or never.
So I don't see the need for an API function.
Why VPP prefers set this flag later?
Would it be better to have some driver-specific flags, no matter the ports?