Hello, I am relatively new to BPF/XDP, and I’m currently trying to use a TC egress program to redirect a packet back to ingress, where I have an XDP program attached. When the XDP program is attached in generic mode (XDP_SKB_MODE), the redirect occurs properly and the packet is seen on the ingress of the interface, but when the program is attached in native mode (XDP_DRV_MODE), the packet never redirects and is just seen exiting the interface, even though the return code of the redirect function is “success”. I've read previous threads that seemed related to this issue, but could not find the answer to my question. I’m trying to understand the difference in behavior between generic versus driver mode, and how to properly redirect the packet in driver mode (if this is possible). I would really appreciate any insight. Here are more details on my setup. When my TC program sees an outgoing packet, it should grab it, make a clone, and redirect the clone to the ingress direction XDP program using bpf_clone_redirect(skb, IFINDEX, BPF_F_INGRESS); When the XDP program is attached in generic mode the packets get redirected successfully and can be seen on the XDP ingress interface (and on tcpdump etc.). However, when the XDP program is attached in xdp native mode (with the NIC provided driver), the packet does not get redirected and simply exits (in this case since I am using the bpf_clone_redirect() helper, two packets are seen exiting). I understand that XDP native mode occurs sooner in the packet processing pipeline than XDP generic mode, and that in native mode there is no skb, but I’m having some trouble understanding exactly what is happening under the hood and how to “fix” it, if possible. My NIC driver is Intel xgbe. I am using bcc to attach and load my xdp and tc programs. I read in this thread https://marc.info/?l=xdp-newbies&m=162344478620095&w=2 that Netronome NICs do not support XDP_REDIRECT, but it seems from this Feb’21 thread https://marc.info/?l=xdp-newbies&m=161362777730255&w=2 that Intel xgbe drivers should support it, although there is additional discussion about potential buggy behavior in a May’21 thread https://marc.info/?l=xdp-newbies&m=162024487722215&w=2. These threads regarding XDP_REDIRECT support in relation to xdp frags also seemed relevant, but since I am new to this area I had some trouble understanding the significance for solving the issue I’m working on. https://marc.info/?l=linux-netdev&m=164275984217304&w=2 https://lore.kernel.org/bpf/YgeUFb4LIP7VfeL9@lore-desk/T/ I would appreciate any insight or advice on understanding the difference between what is happening in xdp generic versus xdp driver modes during a packet redirect from TC egress to XDP ingress whether it is possible to perform a redirect in xdp driver mode with an Intel xgbe driver if yes to 2, how to successfully redirect a packet from TC egress program to XDP ingress program attached in xdp driver mode Thank you very much for your time. Best, Sophia Yoo
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