On Tue, Mar 3, 2020 at 3:50 PM Jakub Kicinski <kuba@xxxxxxxxxx> wrote: > > On Tue, 3 Mar 2020 20:46:55 +0100 Daniel Borkmann wrote: > > Thus, when the data/data_end test fails in generic XDP, the user can > > call e.g. bpf_xdp_pull_data(xdp, 64) to make sure we pull in as much as > > is needed w/o full linearization and once done the data/data_end can be > > repeated to proceed. Native XDP will leave xdp->rxq->skb as NULL, but > > later we could perhaps reuse the same bpf_xdp_pull_data() helper for > > native with skb-less backing. Thoughts? Something akin to pskb_may_pull sounds like a great solution to me. Another approach would be a new xdp_action XDP_NEED_LINEARIZED that causes the program to be restarted after linearization. But that is both more expensive and less elegant. Instead of a sysctl or device option, is this an optimization that could be taken based on the program? Specifically, would XDP_FLAGS be a path to pass a SUPPORT_SG flag along with the program? I'm not entirely familiar with the XDP setup code, so this may be a totally off. But from a quick read it seems like generic_xdp_install could transfer such a flag to struct net_device. > I'm curious why we consider a xdpgeneric-only addition. Is attaching > a cls_bpf program noticeably slower than xdpgeneric? This just should not be xdp*generic* only, but allow us to use any XDP with large MTU sizes and without having to disable GRO. I'd still like a way to be able to drop or modify packets before GRO, or to signal that a type of packet should skip GRO.
