On Fri, Jun 5, 2020 at 1:23 AM Jesper Dangaard Brouer <brouer@xxxxxxxxxx> wrote: > > Great. If we can remove this requirement of -1 init (and let zero mean > feature isn't used), then I'm all for exposing expose in uapi/bpf.h. Not having it in bpf.h doesn't magically make it invisible. It's uapi because user space C sources rely on its fixed format. vmlinux.h contains all kernel types. both uapi and kernel internal. devmap selftest taking uapi 'struct bpf_devmap_val' from vmlinux.h is an awful hack. I prefer to keep vmlinux.h usage to bpf programs only. User space C code should interface with kernel via proper uapi headers. When vmlinux.h is used by bpf C program it's completely different from user space C code doing the same, because llvm emits relocations for bpf prog and libbpf adjusts them. So doing 'foo->bar' in bpf C is specific to target kernel, whereas user C code 'foo->bar' is a hard constant which bakes it into uapi that kernel has to keep backwards compatible. If in some distant future we teach both gcc and clang to do bpf-style relocations for x86 and teach ld.so to adjust them then we can dream about very differently looking kernel/user interfaces. Right now any struct used by user C code and passed into kernel is uapi.
