With growing number of various products and tools using BPF it could easily happen that multiple BPF programs from different processes will be attached to the same tracepoint. It seems that in such case there is no way to specify a custom order in which those programs may want to be executed -- it will depend on the order in which they were attached. Consider an example when the BPF program A is attached to tracepoint T, the BFP program B needs to be attached to the T as well and start before/end after the A (e.g. to monitor the whole process of A + tracepoint in some way). If the program A could not be changed and is attached before B, the order specified above will not be possible. One way to address this in a limited, but less invasive way is to utilize link options structure to pass the desired priority to perf_event_set_bpf_prog, and add new bpf_prog into the bpf_prog_array based on its value. This will allow to specify the priority value via bpf_tracepoint_opts when attaching a new prog. Does this make sense? There maybe a better way to achieve this, I would be glad to hear any feedback on it. Dmitrii Dolgov (2): bpf: tracing: Introduce prio field for bpf_prog libbpf: Allow setting bpf_prog priority drivers/media/rc/bpf-lirc.c | 4 ++-- include/linux/bpf.h | 3 ++- include/linux/trace_events.h | 7 ++++--- include/uapi/linux/bpf.h | 1 + kernel/bpf/core.c | 19 +++++++++++++++++-- kernel/bpf/syscall.c | 3 ++- kernel/events/core.c | 8 ++++---- kernel/trace/bpf_trace.c | 8 +++++--- tools/include/uapi/linux/bpf.h | 1 + tools/lib/bpf/bpf.c | 1 + tools/lib/bpf/bpf.h | 1 + tools/lib/bpf/libbpf.c | 4 +++- tools/lib/bpf/libbpf.h | 6 ++++-- 13 files changed, 47 insertions(+), 19 deletions(-) -- 2.32.0
