Dan Siemon <dan@xxxxxxxxxxxxx> wrote: [ CCing bpf maling list ] > Commit f12064d1b402c60c5db9c4b63d5ed6d7facb33f6 zeros out skb->cb in > br_input.c: > > memset(skb->cb, 0, sizeof(struct br_input_skb_cb)); > > https://github.com/torvalds/linux/commit/f12064d1b402c60c5db9c4b63d5ed6d7facb33f6 > > Prior to 5.2, it was possible to store information in skb->cb and have it > pass through the bridge to the output link. I did not know this was even possible. Any owner of the skb (bridge, ip stack, etc.) use skb->cb[] as they see fit. > We leveraged this to have a BPF > prog that runs on ingress and does custom packet parsing and stores the > output qdisc:class in skb->cb. This enabled the egress BPF filter to be > super simple and avoid having to parse the entire packet again. > > Note I haven't built with this patch removed so it's possible this isn't > the problem but the memset is unconditional... You're not exactly saying what the problem is, so I have no idea. > Is this a regression? Is it expected that the bridge would wipe this field > when just passing frames? Even if you remove the memset, that commit br_input_skb_cb has existed, and is used. Fields were just cleared on-demand rather than unconditionally at the start. I think the latter is better practice and also what other owners do. So please explain what exactly the problem is and/or check that the cb clearing "is the problem". If it is, I have no idea how to fix it.
