On Wed, Feb 9, 2022 at 4:37 AM Quentin Monnet <quentin@xxxxxxxxxxxxx> wrote: > > 2022-02-08 16:39 UTC-0800 ~ Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> > > On Tue, Feb 8, 2022 at 4:07 AM Quentin Monnet <quentin@xxxxxxxxxxxxx> wrote: > >> > >> Since the notion of versions was introduced for bpftool, it has been > >> following the version number of the kernel (using the version number > >> corresponding to the tree in which bpftool's sources are located). The > >> rationale was that bpftool's features are loosely tied to BPF features > >> in the kernel, and that we could defer versioning to the kernel > >> repository itself. > >> > >> But this versioning scheme is confusing today, because a bpftool binary > >> should be able to work with both older and newer kernels, even if some > >> of its recent features won't be available on older systems. Furthermore, > >> if bpftool is ported to other systems in the future, keeping a > >> Linux-based version number is not a good option. > >> > >> Looking at other options, we could either have a totally independent > >> scheme for bpftool, or we could align it on libbpf's version number > >> (with an offset on the major version number, to avoid going backwards). > >> The latter comes with a few drawbacks: > >> > >> - We may want bpftool releases in-between two libbpf versions. We can > >> always append pre-release numbers to distinguish versions, although > >> those won't look as "official" as something with a proper release > >> number. But at the same time, having bpftool with version numbers that > >> look "official" hasn't really been an issue so far. > >> > >> - If no new feature lands in bpftool for some time, we may move from > >> e.g. 6.7.0 to 6.8.0 when libbpf levels up and have two different > >> versions which are in fact the same. > >> > >> - Following libbpf's versioning scheme sounds better than kernel's, but > >> ultimately it doesn't make too much sense either, because even though > >> bpftool uses the lib a lot, its behaviour is not that much conditioned > >> by the internal evolution of the library (or by new APIs that it may > >> not use). > >> > >> Having an independent versioning scheme solves the above, but at the > >> cost of heavier maintenance. Developers will likely forget to increase > >> the numbers when adding features or bug fixes, and we would take the > >> risk of having to send occasional "catch-up" patches just to update the > >> version number. > >> > >> Based on these considerations, this patch aligns bpftool's version > >> number on libbpf's. This is not a perfect solution, but 1) it's > >> certainly an improvement over the current scheme, 2) the issues raised > >> above are all minor at the moment, and 3) we can still move to an > >> independent scheme in the future if we realise we need it. > >> > >> Given that libbpf is currently at version 0.7.0, and bpftool, before > >> this patch, was at 5.16, we use an offset of 6 for the major version, > >> bumping bpftool to 6.7.0. > >> > >> It remains possible to manually override the version number by setting > >> BPFTOOL_VERSION when calling make. > >> > >> Signed-off-by: Quentin Monnet <quentin@xxxxxxxxxxxxx> > >> --- > >> Contrarily to the previous discussion and to what the first patch of the > >> set does, I chose not to use the libbpf_version_string() API from libbpf > >> to compute the version for bpftool. There were three reasons for that: > >> > >> - I don't feel comfortable having bpftool's version number computed at > >> runtime. Somehow it really feels like we should now it when we compile > > > > Fair, but why not use LIBBPF_MAJOR_VERSION and LIBBPF_MINOR_VERSION to > > define BPFTOOL_VERSION (unless it's overridden). > > I forgot the macros were exposed, which is silly, because I was the one > to help expose them in the first place. Anyway. > > > Which all seems to be > > doable at compilation time in C code, not in Makefile. This will work > > with Github version of libbpf just as well with no extra Makefile > > changes (and in general, the less stuff is done in Makefile the > > better, IMO). > > > > Version string can also be "composed" at compile time with a bit of > > helper macro, see libbpf_version_string() implementation in libbpf. > > Sounds good, I can do that. > > This won't give me the patch number, though, only major and minor > version. We could add an additional LIBBPF_PATCH_VERSION to libbpf. > Although thinking about it, I'm not sure we need a patch version for > bpftool at the moment, because changes in libbpf's patch number is > unlikely to reflect any change in bpftool, so it makes little sense to > copy it. So I'm considering just leaving it at 0 in bpftool, and having > updates on major/minor numbers only when libbpf releases a major/minor > version. If we do want bugfix releases, it will still be possible to > overwrite the version number with BPFTOOL_VERSION anyway. What do you think? So the patch version is not currently reflected in libbpf.map file. I do patch version bumps only when we detect some small issue after official release. It happened 2 or 3 times so far. I'm hesitant to expose that as LIBBPF_PATCH_VERSION, because I'll need to remember to bump it manually (and coordinating this between kernel sources and Github is a slow nightmare). Let's not rely on patch version, too much burden. > > Quentin
