On Fri, 27 Jun 2014 17:06:03 -0700, Alexei Starovoitov wrote:
> User interface:
> cat bpf_123 > /sys/kernel/debug/tracing/__event__/filter
>
> where 123 is an id of the eBPF program priorly loaded.
> __event__ is static tracepoint event.
> (kprobe events will be supported in the future patches)
>
> eBPF programs can call in-kernel helper functions to:
> - lookup/update/delete elements in maps
> - memcmp
> - trace_printk
ISTR Steve doesn't like to use trace_printk() (at least for production
kernels) anymore. And I'm not sure it'd work if there's no existing
trace_printk() on a system.
> - load_pointer
> - dump_stack
[SNIP]
> @@ -634,6 +635,15 @@ ftrace_raw_event_##call(void *__data, proto)
> \
> if (ftrace_trigger_soft_disabled(ftrace_file)) \
> return; \
> \
> + if (unlikely(ftrace_file->flags & FTRACE_EVENT_FL_FILTERED) && \
> + unlikely(ftrace_file->event_call->flags & TRACE_EVENT_FL_BPF)) { \
> + struct bpf_context __ctx; \
> + \
> + populate_bpf_context(&__ctx, args, 0, 0, 0, 0, 0); \
> + trace_filter_call_bpf(ftrace_file->filter, &__ctx); \
> + return; \
> + } \
> + \
Hmm.. But it seems the eBPF prog is not a filter - it'd always drop the
event. And I think it's better to use a recorded entry rather then args
as a bpf_context so that tools like perf can manipulate it at compile
time based on the event format.
Thanks,
Namhyung
> __data_size = ftrace_get_offsets_##call(&__data_offsets, args); \
> \
> entry = ftrace_event_buffer_reserve(&fbuffer, ftrace_file, \
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