On Wed, Nov 03, 2021 at 04:46:42AM IST, Alexei Starovoitov wrote: > On Sat, Oct 30, 2021 at 08:16:03PM +0530, Kumar Kartikeya Dwivedi wrote: > > This series adds unstable conntrack lookup helpers using BPF kfunc support. The > > patch adding the lookup helper is based off of Maxim's recent patch to aid in > > rebasing their series on top of this, all adjusted to work with kfunc support > > [0]. > > > > This is an RFC series, as I'm unsure whether the reference tracking for > > PTR_TO_BTF_ID will be accepted. > > Yes. The patches look good overall. > Please don't do __BPF_RET_TYPE_MAX signalling. It's an ambiguous name. > _MAX is typically used for a different purpose. Just give it an explicit name. > I don't fully understand why that skip is needed though. I needed a sentinel to skip return type checking (otherwise check that return type and prototype match) since existing kfunc don't have a get_kfunc_return_type callback, but if we add bpf_func_proto support to kfunc then we can probably convert existing kfuncs to that as well and skip all this logic. Mostly needed it for RET_PTR_TO_BTF_ID_OR_NULL. Extending to support bpf_func_proto seemed like a bit of work so I wanted to get some feedback first on all this, before working on it. > Why it's not one of existing RET_*. Duplication of return and > being lazy to propagate the correct ret value into get_kfunc_return_type ? > > > If not, we can go back to doing it the typical > > way with PTR_TO_NF_CONN type, guarded with #if IS_ENABLED(CONFIG_NF_CONNTRACK). > > Please don't. We already have a ton of special and custom types in the verifier. > refcnted PTR_TO_BTF_ID sounds as good way to scale it. > Understood. > > Also, I want to understand whether it would make sense to introduce > > check_helper_call style bpf_func_proto based argument checking for kfuncs, or > > continue with how it is right now, since it doesn't seem correct that PTR_TO_MEM > > can be passed where PTR_TO_BTF_ID may be expected. Only PTR_TO_CTX is enforced. > > Do we really allow to pass PTR_TO_MEM argument into a function that expects PTR_TO_BTF_ID ? Sorry, that's poorly phrased. Current kfunc doesn't support PTR_TO_MEM. I meant it would be allowed now, with the way I implemented things, but there also isn't a way to signal whether PTR_TO_BTF_ID is expected (hence the question about bpf_func_proto). I did not understand why that was not done originally (maybe it was lack of usecase). PTR_TO_CTX works because the type is matched with prog type, so you can't pass something else there. For other cases the type of register is considered. > That sounds like a bug that we need to fix. -- Kartikeya
