From: Jon Doron <jond@xxxxxx> Add support for writing a custom event reader, by exposing the ring buffer state, and allowing to set it's tail. Few simple examples where this type of needed: 1. perf_event_read_simple is allocating using malloc, perhaps you want to handle the wrap-around in some other way. 2. Since perf buf is per-cpu then the order of the events is not guarnteed, for example: Given 3 events where each event has a timestamp t0 < t1 < t2, and the events are spread on more than 1 CPU, then we can end up with the following state in the ring buf: CPU[0] => [t0, t2] CPU[1] => [t1] When you consume the events from CPU[0], you could know there is a t1 missing, (assuming there are no drops, and your event data contains a sequential index). So now one can simply do the following, for CPU[0], you can store the address of t0 and t2 in an array (without moving the tail, so there data is not perished) then move on the CPU[1] and set the address of t1 in the same array. So you end up with something like: void **arr[] = [&t0, &t1, &t2], now you can consume it orderely and move the tails as you process in order. Jon Doron (1): libbpf: perfbuf: allow raw access to buffers tools/lib/bpf/libbpf.c | 40 ++++++++++++++++++++++++++++++++++++++++ tools/lib/bpf/libbpf.h | 6 ++++++ 2 files changed, 46 insertions(+) -- 2.36.1
