Helper function bpf_skb_change_tail
Definition
Copyright (c) 2015 The Libbpf Authors. All rights reserved.
Resize (trim or grow) the packet associated to skb to the new len. The flags are reserved for future usage, and must be left at zero.
The basic idea is that the helper performs the needed work to change the size of the packet, then the eBPF program rewrites the rest via helpers like bpf_skb_store_bytes(), bpf_l3_csum_replace(), bpf_l3_csum_replace() and others. This helper is a slow path utility intended for replies with control messages. And because it is targeted for slow path, the helper itself can afford to be slow: it implicitly linearizes, unclones and drops offloads from the skb.
A call to this helper is susceptible to change the underlying packet buffer. Therefore, at load time, all checks on pointers previously done by the verifier are invalidated and must be performed again, if the helper is used in combination with direct packet access.
Returns
0 on success, or a negative error in case of failure.
static long (* const bpf_skb_change_tail)(struct __sk_buff *skb, __u32 len, __u64 flags) = (void *) 38;
Usage
Docs could be improved
This part of the docs is incomplete, contributions are very welcome
Program types
This helper call can be used in the following program types:
Example
Docs could be improved
This part of the docs is incomplete, contributions are very welcome