From: Jakub Kicinski <kubak...@wp.pl> Date: Tue, 11 Apr 2017 11:34:25 -0700
> On Tue, 11 Apr 2017 18:43:47 +0200, Daniel Borkmann wrote: >> cls_bpf has a couple of helpers like bpf_l3_csum_replace(), >> bpf_l4_csum_replace() >> bpf_csum_diff(), bpf_csum_update(), where we (cilium at least) use checksum >> diffs extensively. You can then also leave the option to the user to feed >> pre-computed diffs from a map, etc, or, to just not care at all when not >> necessary. Pushing this via return code seems a bit odd, perhaps a xdp->csum >> member could be populated before calling into the program and the resulting >> xdp->csum processed further upon exit. > > +1 on exposing xdp->csum. I think having the csum complete available > in the eBPF program (rather than diff) may be useful for apps doing > encap to a csumed tunnel (e.g. UDP). If the header is pre-calculated > in the map, having csum complete makes calculating the outer csum > extremely easy, right? The outer checksum is constant because when the inner checksum is installed the inner frame checksums to zero. I really want to see how people are actually changing fields in XDP that requires special checksum facilities, that isn't already handled using the csum helpers Daniel mentioned.
