From: Andrii Nakryiko <andrii@xxxxxxxxxx> Map name that's assigned to internal maps (.rodata, .data, .bss, etc) consist of a small prefix of bpf_object's name and ELF section name as a suffix. This makes it hard for users to "guess" the name to use for looking up by name with bpf_object__find_map_by_name() API. One proposal was to drop object name prefix from the map name and just use ".rodata", ".data", etc, names. One downside called out was that when multiple BPF applications are active on the host, it will be hard to distinguish between multiple instances of .rodata and know which BPF object (app) they belong to. Having few first characters, while quite limiting, still can give a bit of a clue, in general. Another downside of such approach is that it is not backwards compatible and, among direct use of bpf_object__find_map_by_name() API, will break any BPF skeleton generated using bpftool that was compiled with older libbpf version. Instead of causing all this pain, libbpf will still generate map name using a combination of object name and ELF section name, but it will allow looking such maps up by their natural names, which correspond to their respective ELF section names. This means non-truncated ELF section names longer than 15 characters are going to be expected and supported. With such set up, we get the best of both worlds: leave small bits of a clue about BPF application that instantiated such maps, as well as making it easy for user apps to lookup such maps at runtime. In this sense it closes corresponding libbpf 1.0 issue ([0]). BPF skeletons will continue using full names for lookups. [0] Closes: https://github.com/libbpf/libbpf/issues/275 Cc: Toke Høiland-Jørgensen <toke@xxxxxxxxxx> Cc: Stanislav Fomichev <sdf@xxxxxxxxxx> Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx> --- tools/lib/bpf/libbpf.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c index 054549846025..01ebdb8a36d1 100644 --- a/tools/lib/bpf/libbpf.c +++ b/tools/lib/bpf/libbpf.c @@ -9037,6 +9037,16 @@ bpf_object__find_map_by_name(const struct bpf_object *obj, const char *name) struct bpf_map *pos; bpf_object__for_each_map(pos, obj) { + /* if it's a special internal map name (which always starts + * with dot) then check if that special name matches the + * real map name (ELF section name) + */ + if (name[0] == '.') { + if (pos->real_name && strcmp(pos->real_name, name) == 0) + return pos; + continue; + } + /* otherwise map name has to be an exact match */ if (map_uses_real_name(pos)) { if (strcmp(pos->real_name, name) == 0) return pos; -- 2.30.2
