Re: bpf_redirect and xdpgeneric

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On Fri, 18 Sep 2020 14:27:45 -0600
David Ahern <dsahern@xxxxxxxxx> wrote:

> On 9/18/20 12:42 PM, Thomas Ptacek wrote:
> > The setup is pretty simple. There's an eno1 (igb driver), to which our
> > default route points. On the same box are several VMs. There's a tap
> > interface (for each VM, call it tapX). Traffic for a VM flows in from
> > the Internet on eno1 and is directed to tapX; the response traffic
> > flows in the other direction.
> > 
> > I'm deliberately simplifying here:
> > 
> > eno1 runs an XDP program that does some lightweight IP rewriting from
> > anycast addresses to internal VM addresses on ingress. eno1's XDP
> > program currently XDP_PASS's rewritten packets to the IP stack, where
> > they're routed to the VM's tap. This works fine.
> > 
> > tapX runs an XDP program that does the same rewriting in reverse.
> > Right now, it also XDP_PASS's packets to the stack, which also works
> > --- the stack routes response traffic out eno1.
> > 
> > I'm playing with XDP_REDIRECT'ing instead of XDP_PASS'ing.
> > 
> > I have the ifindexes and MAC addresses (and those of IP neighbors) in
> > a map --- a normal HASH map, not a DEVMAP. Using that map, I can
> > successfully redirect traffic from tapX to arbitrary other tap
> > interfaces. What I can't do is redirect packets from tapX to eno1,
> > which is what the system actually needs to do.
> >   
> XDP_REDIRECT sends the packet to a devices ndo_xdp_xmit function. tap
> implements it hence eno1 -> tap works; igb does not meaning tap -> eno1
> fails.

There is clearly a real-life use-case for adding native-XDP support for
igb driver.  Sven (cc) have implemented this (v6[1]), but something is
causing this patch to not move forward, what is stalling Intel maintainers?

To Thomas, you could try out the patch[2] and report back if it works
for you?  (I think it will help moving patch forward...)

Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat

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