Re: [PATCH RFC v4 net-next 17/26] tracing: allow eBPF programs to be attached to events

From: Alexei Starovoitov
Date: Fri Aug 15 2014 - 15:35:27 EST

On Fri, Aug 15, 2014 at 12:18 PM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:
>> clang/llvm has no problem with u64 :)
>> This bpf_context struct for tracing is trying to answer the question:
>> 'what's the most convenient way to access tracepoint arguments
>> from a script'.
>> When kernel code has something like:
>> trace_kfree_skb(skb, net_tx_action);
>> the script needs to be able to access this 'skb' and 'net_tx_action'
>> values through _single_ data structure.
>> In this proposal they are ctx->arg1 and ctx->arg2.
>> I've considered having different bpf_context's for every event, but
>> the complexity explodes. I need to hack all event definitions and so on.
>> imo it's better to move complexity to userspace, so program author
>> or high level language abstracts these details.
> I still don't understand why making them long instead of u64 is
> helpful, though. I feel like I'm missing obvious here.

I promise to come back to this... Have to go off grid...
will think of it in the mean time... Appreciate this discussion!!
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