Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> writes: > On Fri, Mar 27, 2020 at 5:58 AM Toke Høiland-Jørgensen <toke@xxxxxxxxxx> wrote: >> >> For internal maps (most notably the maps backing global variables), libbpf >> uses an internal mmaped area to store the data after opening the object. >> This data is subsequently copied into the kernel map when the object is >> loaded. >> >> This adds a getter for the pointer to that internal data store. This can be >> used to modify the data before it is loaded into the kernel, which is >> especially relevant for RODATA, which is frozen on load. This same pointer >> is already exposed to the auto-generated skeletons, so access to it is >> already API; this just adds a way to get at it without pulling in the full >> skeleton infrastructure. >> >> Signed-off-by: Toke Høiland-Jørgensen <toke@xxxxxxxxxx> >> --- >> v2: >> - Add per-map getter for data area instead of a global rodata getter for bpf_obj >> >> tools/lib/bpf/libbpf.c | 9 +++++++++ >> tools/lib/bpf/libbpf.h | 1 + >> tools/lib/bpf/libbpf.map | 1 + >> 3 files changed, 11 insertions(+) >> >> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c >> index 085e41f9b68e..a0055f8908fd 100644 >> --- a/tools/lib/bpf/libbpf.c >> +++ b/tools/lib/bpf/libbpf.c >> @@ -6756,6 +6756,15 @@ void *bpf_map__priv(const struct bpf_map *map) >> return map ? map->priv : ERR_PTR(-EINVAL); >> } >> >> +void *bpf_map__data_area(const struct bpf_map *map, size_t *size) > > I'm not entirely thrilled about "data_area" name. This is entirely for > providing initial value for maps, so maybe something like > bpf_map__init_value() or something along those lines? > > Actually, how about a different API altogether: > > bpf_map__set_init_value(struct bpf_map *map, void *data, size_t size)? > > Application will have to prepare data of correct size, which will be > copied to libbpf's internal storage. It also doesn't expose any of > internal pointer. I don't think extra memcopy is a big deal here. > Thoughts? Huh, yeah, that's way better. Why didn't I think of that? Think maybe I was too focused on doing this the same way the skeleton code is. I'll send a v3 :) -Toke
