bpftool: Enable libbpf's strict mode by default

Otherwise, attaching with bpftool doesn't work with strict section names.

Also:

  - Add --legacy option to switch back to pre-1.0 behavior
  - Print a warning when program fails to load in strict mode to
    point to --legacy flag
  - By default, don't append / to the section name; in strict
    mode it's relevant only for a small subset of prog types

+ bpftool --legacy prog loadall tools/testing/selftests/bpf/test_cgroup_link.o /sys/fs/bpf/kprobe type kprobe
libbpf: failed to pin program: File exists
Error: failed to pin all programs
+ bpftool prog loadall tools/testing/selftests/bpf/test_cgroup_link.o /sys/fs/bpf/kprobe type kprobe

v1 -> v2:
  - strict by default (Quentin Monnet)
  - add more info to --legacy description (Quentin Monnet)
  - add bash completion (Quentin Monnet)

Signed-off-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Quentin Monnet <quentin@isovalent.com>
Link: https://lore.kernel.org/bpf/20211110192324.920934-1-sdf@google.com

1 files changed, 24 insertions, 16 deletions

diff --git a/tools/bpf/bpftool/prog.c b/tools/bpf/bpftool/prog.c
index dea7a49ec26e..bf85c914f2fa 100644
--- a/tools/bpf/bpftool/prog.c
+++ b/tools/bpf/bpftool/prog.c
@@ -1483,8 +1483,6 @@ static int load_with_options(int argc, char **argv, bool first_prog_only)
 
 	while (argc) {
 		if (is_prefix(*argv, "type")) {
-			char *type;
-
 			NEXT_ARG();
 
 			if (common_prog_type != BPF_PROG_TYPE_UNSPEC) {
@@ -1494,21 +1492,26 @@ static int load_with_options(int argc, char **argv, bool first_prog_only)
 			if (!REQ_ARGS(1))
 				goto err_free_reuse_maps;
 
-			/* Put a '/' at the end of type to appease libbpf */
-			type = malloc(strlen(*argv) + 2);
-			if (!type) {
-				p_err("mem alloc failed");
-				goto err_free_reuse_maps;
-			}
-			*type = 0;
-			strcat(type, *argv);
-			strcat(type, "/");
+			err = libbpf_prog_type_by_name(*argv, &common_prog_type,
+						       &expected_attach_type);
+			if (err < 0) {
+				/* Put a '/' at the end of type to appease libbpf */
+				char *type = malloc(strlen(*argv) + 2);
 
-			err = get_prog_type_by_name(type, &common_prog_type,
-						    &expected_attach_type);
-			free(type);
-			if (err < 0)
-				goto err_free_reuse_maps;
+				if (!type) {
+					p_err("mem alloc failed");
+					goto err_free_reuse_maps;
+				}
+				*type = 0;
+				strcat(type, *argv);
+				strcat(type, "/");
+
+				err = get_prog_type_by_name(type, &common_prog_type,
+							    &expected_attach_type);
+				free(type);
+				if (err < 0)
+					goto err_free_reuse_maps;
+			}
 
 			NEXT_ARG();
 		} else if (is_prefix(*argv, "map")) {
@@ -1731,6 +1734,11 @@ err_unpin:
 	else
 		bpf_object__unpin_programs(obj, pinfile);
 err_close_obj:
+	if (!legacy_libbpf) {
+		p_info("Warning: bpftool is now running in libbpf strict mode and has more stringent requirements about BPF programs.\n"
+		       "If it used to work for this object file but now doesn't, see --legacy option for more details.\n");
+	}
+
 	bpf_object__close(obj);
 err_free_reuse_maps:
 	for (i = 0; i < old_map_fds; i++)