On Fri, Jul 30, 2021 at 1:23 PM Quentin Monnet <quentin@xxxxxxxxxxxxx> wrote: > > On Fri, 30 Jul 2021 at 18:24, Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> wrote: > > [...] > > > > > The right approach will be to define > > > > LIBBPF_MAJOR_VERSION/LIBBPF_MINOR_VERSION in some sort of > > > > auto-generated header, included from libbpf_common.h and installed as > > > > part of libbpf package. > > > > > > So generating this header is easy. Installing it with the other headers > > > is simple too. It becomes a bit trickier when we build outside of the > > > directory (it seems I need to pass -I$(OUTPUT) to build libbpf). > > > > Not sure why using the header is tricky. We auto-generate > > bpf_helper_defs.h, which is included from bpf_helpers.h, which is > > included in every single libbpf-using application. Works good with no > > extra magic. > > bpf_helper_defs.h is the first thing I looked at, and I processed > libbpf_version.h just like it. But there is a difference: > bpf_helper_defs.h is _not_ included in libbpf itself, nor is it needed > in bpftool at the bootstrap stage (it is only included from the eBPF > skeletons for profiling or showing PIDs etc., which are compiled after > libbpf). The version header is needed in both cases. Oh, in that sense. Yeah, sure, I didn't think that would qualify as tricky. But yeah, -I$(OUTPUT) or something along those lines is fine. > > > > > > > > > The step I'm most struggling with at the moment is bpftool, which > > > bootstraps a first version of itself before building libbpf, by looking > > > at the headers directly in libbpf's directory. It means that the > > > generated header with the version number has not yet been generated. Do > > > you think it is worth changing bpftool's build steps to implement this > > > deprecation helper? > > > > If it doesn't do that already, bpftool should do `make install` for > > libbpf, not just build. Install will put all the headers, generated or > > otherwise, into a designated destination folder, which should be > > passed as -I parameter. But that should be already happening due to > > bpf_helper_defs.h. > > bpftool does not run "make install". It compiles libbpf passing > "OUTPUT=$(LIBBPF_OUTPUT)", sets LIBBPF_PATH to the same directory, and > then adds "-I$(LIBBPF_PATH)" for accessing bpf_helper_defs.h and compile > its eBPF programs. It is possible to include libbpf_version.h the same > way, but only after libbpf has been compiled, after the bootstrap. > > I'll look into updating the Makefile to compile and install libbpf > before the bootstrap, when I have some time. Cool, `make install` is the best way as it prevents accidental usage of libbpf's internal header. So it's a good change to make.
