Parsing Non linear packet payload in TC BPF programs
We are parsing DHCP packets in TC egress program, In our case, the packet after the UDP header was not present in between skb->data and skb->data_end. On further investigation we found that it lies in non-linear portion. and we have bpf_skb_pull_data(skb,len) to direct access non-linear data.
Few questions based on above:
1. After call to bpf_skb_pull_data(skb, skb->len); the value of skb->data and skb->data_end pointers changed. Can there be any implication down the stack with change in value of skb->data pointer. Also is this helper function analogous to skb_pull which changes the skb->data pointer and is typically moved when the packet goes up the stack as a result of packet being parsed on that layer? Do we have something similar to skb_linearize() in BPF or any other way to parse non-linear portion?
2. For our case, packet after the UDP header was in non-linear portion, can it happen that packet after IP header go in non-linear or packet after ethernet-header?