On Mon, Jul 23, 2018 at 02:21:05PM -0400, Andrew Wang wrote:
> Hi
>
> I am writing a bpf program for packet processing and have loaded my ingress
> function at BPF.XDP.
>
> I'm updating the destination IPv6 address and want to update the TCP
> checksum, but when I try to call the helper functions "bpf_csum_diff" or
> "bpf_l4_csum_replace", I get a "unknown func <function name>". Are these
> functions not available for XDP program types?
XDP programs cannot use bpf_l4_csum_replace, but they can use
bpf_csum_diff since commit 205c380 ("bpf: add csum_diff helper to xdp as
well") which landed in v4.16-rc1.
>
> Is there a way to tell what helper functions are available to what program
> types?
The list of helpers available to XDP programs is defined in function
xdp_func_proto in file net/core/filter.c of the Linux source code.
You might also want to check out pull request #1881 [1], which will
document helpers available to each program type in file kernel-versions.md
of bcc [2].
1 - https://github.com/iovisor/bcc/pull/1881
2 - https://github.com/iovisor/bcc/blob/master/docs/kernel-versions.md
>
> Thanks
> Andrew
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