On Sun, Apr 3, 2022 at 9:08 AM Dmitrii Dolgov <9erthalion6@xxxxxxxxx> wrote: > > 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. Not really. What's the real use case where you need to define relative order of BPF programs on the same kprobe or tracepoint. Each of them is supposed to be independent of each other and not depend on any order of their execution. Further, given such tracing programs are read-only relative to the kernel (they can't change kernel behavior), the order is supposed to be irrelevant. > > 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 >
