2022-02-09 09:53 UTC-0800 ~ Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> > 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. ... Except that you can only compose so much. The preprocessor won't allow me to sum libbpf's major version with the offset (6) before turning it into a string. I need to think about this a bit more. >> >> 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. Agreed, thanks. Quentin
