From d76198b0bc5a67c14c5209bac82481399a3387da Mon Sep 17 00:00:00 2001 From: Jakub Kicinski Date: Mon, 28 Jan 2019 10:29:15 -0800 Subject: [PATCH] tools: bpftool: warn about risky prog array updates When prog array is updated with bpftool users often refer to the map via the ID. Unfortunately, that's likely to lead to confusion because prog arrays get flushed when the last user reference is gone. If there is no other reference bpftool will create one, update successfully just to close the map again and have it flushed. Warn about this case in non-JSON mode. If the problem continues causing confusion we can remove the support for referring to a map by ID for prog array update completely. For now it seems like the potential inconvenience to users who know what they're doing outweighs the benefit. Signed-off-by: Jakub Kicinski Reviewed-by: Quentin Monnet Acked-by: Song Liu Signed-off-by: Daniel Borkmann --- tools/bpf/bpftool/map.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/tools/bpf/bpftool/map.c b/tools/bpf/bpftool/map.c index f15c520195b7..2160a8ef17e5 100644 --- a/tools/bpf/bpftool/map.c +++ b/tools/bpf/bpftool/map.c @@ -426,6 +426,9 @@ static int parse_elem(char **argv, struct bpf_map_info *info, p_err("not enough value arguments for map of progs"); return -1; } + if (is_prefix(*argv, "id")) + p_info("Warning: updating program array via MAP_ID, make sure this map is kept open\n" + " by some process or pinned otherwise update will be lost"); fd = prog_parse_fd(&argc, &argv); if (fd < 0) -- 2.30.2