Still use a sensible default of 9216, but if the L3 packet size is set
on the VPP interface, copy it forward (just as we do in the 'host'
interface of the TAP itself, ie the interface created in the linux
namespace). Now they will all line up initially.
The TAP interface does copy forward the host MTU based on the VPP
interface's L3 MTU, but it should also ensure that the VPP tap
interface has an MTU that is greater-or-equal to those. Considering
users can set the interfaces at runtime (set interface mtu packet ...)
ensure that the tap MTU is large enough.
Ideally, a callback updates the MTU to the same value as the L3 MTU of
the VPP interface, or the L3 MTU of the host interface, if either of
those change. For now, it's a safe bet to take jumbo 9216.
This gives a lot of operational problems later. It's definitely reasonable
to be able to create tap interfaces in other namespaces, and this is
still possible (see below for syntax).
However, changing the runtime netns makes the netlink listener much more
complicated because it will have to listen on not just one netns, but all
of them, for netlink updates.
So, for now, let's remove the ability to set the namespace in the API.
Still possible:
- set at startup.conf in lcpng { netns <x> }
- force creating in 'lcpng create ... netns <x>'
This will nudge folks to create one singular namespace (say,
'dataplane', in the startup.conf), and then handle all netlink messages
in that namespace only.
