Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> writes: > On Tue, Feb 4, 2020 at 11:19 AM Toke Høiland-Jørgensen <toke@xxxxxxxxxx> wrote: >> >> Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> writes: >> >> > On Tue, Feb 4, 2020 at 12:25 AM Toke Høiland-Jørgensen <toke@xxxxxxxxxx> wrote: >> >> >> >> Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> writes: >> >> >> >> > On Mon, Feb 3, 2020 at 8:53 PM David Ahern <dsahern@xxxxxxxxx> wrote: >> >> >> >> >> >> On 2/3/20 8:41 PM, Andrii Nakryiko wrote: >> >> >> > On Mon, Feb 3, 2020 at 5:46 PM David Ahern <dsahern@xxxxxxxxx> wrote: >> >> >> >> >> >> >> >> On 2/3/20 5:56 PM, Andrii Nakryiko wrote: >> >> >> >>> Great! Just to disambiguate and make sure we are in agreement, my hope >> >> >> >>> here is that iproute2 can completely delegate to libbpf all the ELF >> >> >> >>> >> >> >> >> >> >> >> >> iproute2 needs to compile and continue working as is when libbpf is not >> >> >> >> available. e.g., add check in configure to define HAVE_LIBBPF and move >> >> >> >> the existing code and move under else branch. >> >> >> > >> >> >> > Wouldn't it be better to statically compile against libbpf in this >> >> >> > case and get rid a lot of BPF-related code and simplify the rest of >> >> >> > it? This can be easily done by using libbpf through submodule, the >> >> >> > same way as BCC and pahole do it. >> >> >> > >> >> >> >> >> >> iproute2 compiles today and runs on older distributions and older >> >> >> distributions with newer kernels. That needs to hold true after the move >> >> >> to libbpf. >> >> > >> >> > And by statically compiling against libbpf, checked out as a >> >> > submodule, that will still hold true, wouldn't it? Or there is some >> >> > complications I'm missing? Libbpf is designed to handle old kernels >> >> > with no problems. >> >> >> >> My plan was to use the same configure test I'm using for xdp-tools >> >> (where I in turn copied the structure of the configure script from >> >> iproute2): >> >> >> >> https://github.com/xdp-project/xdp-tools/blob/master/configure#L59 >> >> >> >> This will look for a system libbpf install and compile against it if it >> >> is compatible, and otherwise fall back to a statically linking against a >> >> git submodule. >> > >> > How will this work when build host has libbpf installed, but target >> > host doesn't? You'll get dynamic linker error when trying to run that >> > tool. >> >> That's called dependency tracking; distros have various ways of going >> about that :) > > I'm confused, honestly. libbpf is either a dependency and thus can be > relied upon to be present in the target system, or it's not and this > whole dance with detecting libbpf presence needs to be performed. Yes, and iproute2 is likely to be built in both sorts of environments, so we will have to support both :) > If libbpf is optional, then I don't see how iproute2 BPF-related code > and complexity can be reduced at all, given it should still support > loading BPF programs even without libbpf. Furthermore, given libbpf > supports more features already and will probably be outpacing > iproute2's own BPF support in the future, some users will start > relying on BPF features supported only by libbpf "backend", so > iproute2's own BPF backend will just fail to load such programs, > bringing unpleasant surprises, potentially. So I still fail to see how > libbpf can be optional and what benefit does that bring. I wasn't saying that libbpf itself should be optional; if we're porting things, we should rip out as much of the old code as we can. I just meant that we should support both modes of building, so distros that *do* build libbpf as a library can link iproute2 against that with as little friction as possible. I'm dead set on a specific auto-detection semantic either; I guess it'll be up to the iproute2 maintainers whether they prefer defaulting to one or the other. > But shared or static - whatever fits iproute2 best, no preferences. Right, cool, I think we are basically agreed, given the above :) -Toke
