Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> writes: > On Wed, Apr 14, 2021 at 7:26 PM Grant Seltzer Richman > <grantseltzer@xxxxxxxxx> wrote: >> >> As I understand it, accessing and setting read only global variables >> from a userspace control program through libbpf can only happen when >> importing a BPF skeleton. Things like `bpf_object__find_map_by_name()` >> are exposed but the name of this map is internal and >> `internal_map_name()` is as well. Traversing through the maps array >> via bpf_object directly doesn't seem possible either. > > Not really. > > See bpf_object__for_each_map() macro and bpf_map__is_internal() API, > both of which are public. As for the name, it's also sort of part of > API, though I want to fix them in libbpf 1.0 (they should be named > .rodata, .data, .bss). So you can definitely either find the map with > iteration or by knowing how the name is generated. Then do mmap() and > using BTF you'll know each variable's offset and size. No magic, just > some code to do this, which is what is done by bpftool for skeletons > (bpftool is a completely external user of libbpf in this case, no > private APIs are involved). We also added bpf_map__set_initial_value() for this, so you don't even need to mmap(); we're using this in libxdp: https://github.com/xdp-project/xdp-tools/blob/master/lib/libxdp/libxdp.c#L2325 -Toke
