Re: [patch net-next RFC 0/4] introduce infrastructure for support of switch chip datapath

[Thomas Graf <tgraf@suug.ch>]

On 03/26/14 at 07:10am, Neil Horman wrote:
> But by creating net_devices that are registered in the current fashion we
> implicitly agree to levels of functionality that are assumed to be available and
> as such are not within the purview of a net_device to reject.  E.g. it is
> assumed that a netdevice can filter frames using iptables/ebtables, limit
> traffic using tc, etc.

I think this is the point where we disagree. We already have several
devices that hook into the rx handler and never have their packets
pass through either iptables or ebtables. Better examples of this are
macvtap or OVS.

What should happen is that these devices are given a chance to implement
the ACL in their own flow table. If no such facility exists, the rule
insertion should fall back to software mode if that is possible (an
OF capable switching chip could insert a 'upcall' flow), or as
a last resort return an error to indicate EOPNOTSUPP.

> And if a switch fabric is short cutting traffic so that
> the cpu doesn't see them, those bits of functionality won't work.  I agree we
> can likely work around that with richer feature capabilities, but such an
> infrastructure would both require extensive kernel changes to fully cover the
> set of existing features at a sufficient granularity, and require user space
> changes to grok the feature set of a given device.  Not saying its impossibible
> or even undesireable mind you, just thats its not any less invasive than what
> I'm proposing.

What I don't understand at this point is how hiding the ports behind
a master device would buy us anything. We would still need to abstract
the filtering capabilities of the ports at some level and hiding that
behind existing tools seems to most convenient way.