quoted

So I've [finally] started looking into implementing XDP for qede, and
there's one thing I feel like I'm missing in regard to XDP_TX - what's
the guarantee/requirement that the bpf program isn't going to
transmute some fields of the rx packet in a way that would prevent the
forwarding?

I think there are really two separate questions you're probably asking. 1) Can
XDP modify a packet in such a way that it won't be forwarded by the driver when
XDP_TX is returned, ie. driver would drop packet  2) Does anything prevent the
BPF program from modifying the packet such that it becomes malformed (bad
checksum, mangled headers, etc.).

I believe the answer to #1 is "no", the XDP interface assumes raw packets. If
program returns XDP_TX then the driver will forward the raw packet without any
further consideration.

The answer to #2 is "no", there is no check that packet produced is sensible. We
assume that the user setting the XDP program knows what they are doing.

O.k., thanks - so I can safely assume forwarding wouldn't require any HW offloading.

BTW, are we considering some offload where the eBPF would return  a set
of changes [based on some pre-set capabilities set by driver] done on buffer
and let the HW offload those?

I understand end goal is eBPF hw-offloading, but seems like there are a lot of
existing offload facilities that might be leveraged.