On 02/27/2018 01:32 AM, Tushar Dave wrote:
> Hello,
>
> I am writing sample eBPF kernel program that uses kprobe
> e.g.
> SEC("kprobe/xyz")
> int bpf_prog1(struct pt_regs *ctx)
> {
> .
> ..
> }
>
> And with pt_regs context I retrieved pointer to 'struct sk_buff_head'.
> From here on, I want to iterate over all skbs in the skb queue and
> print/gather packet data. This certainly involves loop and that causes
> my ebpf kernel program to fail with error,
> e.g.
> bpf_load_program() err=22
> back-edge from insn 51 to 39
> back-edge from insn 51 to 39
>
> Any other alternative so that I can retrieve all packet data from skb queue?
>
> Apology as this is not pure xdp query but I feel it should be okay to
> ask here.
Bounded loops are still wip in BPF core, but today you can make use of
loop unrolling like the following when <X> is a known constant:
#pragma unroll
for (i = 0; i < <X>; i++) {
[...]
}
I presume you're walking the skb via bpf_probe_read() helper from tracing
side, right? Other option could be to add a networking program (e.g. via
cls_bpf) and dump the full skb to perf RB via bpf_skb_event_output() helper.
Potentially if you already dump other data from tracing side via perf RB,
then the networking program can reuse/share the very same perf event map
as well.
Cheers,
Daniel
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