Merge branch 'bpf_iter-uapi-fix'

Yonghong Song says:

====================
Andrii raised a concern that current uapi for bpf iterator map
element is a little restrictive and not suitable for future potential
complex customization. This is a valid suggestion, considering people
may indeed add more complex custimization to the iterator, e.g.,
cgroup_id + user_id, etc. for task or task_file. Another example might
be map_id plus additional control so that the bpf iterator may bail
out a bucket earlier if a bucket has too many elements which may hold
lock too long and impact other parts of systems.

Patch #1 modified uapi with kernel changes. Patch #2
adjusted libbpf api accordingly.

Changelogs:
  v3 -> v4:
    . add a forward declaration of bpf_iter_link_info in
      tools/lib/bpf/bpf.h in case that libbpf is built against
      not-latest uapi bpf.h.
    . target the patch set to "bpf" instead of "bpf-next"
  v2 -> v3:
    . undo "not reject iter_info.map.map_fd == 0" from v1.
      In the future map_fd may become optional, so let us use map_fd == 0
      indicating the map_fd is not set by user space.
    . add link_info_len to bpf_iter_attach_opts to ensure always correct
      link_info_len from user. Otherwise, libbpf may deduce incorrect
      link_info_len if it uses different uapi header than the user app.
  v1 -> v2:
    . ensure link_create target_fd/flags == 0 since they are not used. (Andrii)
    . if either of iter_info ptr == 0 or iter_info_len == 0, but not both,
      return error to user space. (Andrii)
    . do not reject iter_info.map.map_fd == 0, go ahead to use it trying to
      get a map reference since the map_fd is required for map_elem iterator.
    . use bpf_iter_link_info in bpf_iter_attach_opts instead of map_fd.
      this way, user space is responsible to set up bpf_iter_link_info and
      libbpf just passes the data to the kernel, simplifying libbpf design.
      (Andrii)
====================

Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 6 insertions, 3 deletions

diff --git a/tools/bpf/bpftool/iter.c b/tools/bpf/bpftool/iter.c
index c9dba7543dba..3b1aad7535dd 100644
--- a/tools/bpf/bpftool/iter.c
+++ b/tools/bpf/bpftool/iter.c
@@ -11,6 +11,7 @@
 static int do_pin(int argc, char **argv)
 {
 	DECLARE_LIBBPF_OPTS(bpf_iter_attach_opts, iter_opts);
+	union bpf_iter_link_info linfo;
 	const char *objfile, *path;
 	struct bpf_program *prog;
 	struct bpf_object *obj;
@@ -36,6 +37,11 @@ static int do_pin(int argc, char **argv)
 			map_fd = map_parse_fd(&argc, &argv);
 			if (map_fd < 0)
 				return -1;
+
+			memset(&linfo, 0, sizeof(linfo));
+			linfo.map.map_fd = map_fd;
+			iter_opts.link_info = &linfo;
+			iter_opts.link_info_len = sizeof(linfo);
 		}
 	}
 
@@ -57,9 +63,6 @@ static int do_pin(int argc, char **argv)
 		goto close_obj;
 	}
 
-	if (map_fd >= 0)
-		iter_opts.map_fd = map_fd;
-
 	link = bpf_program__attach_iter(prog, &iter_opts);
 	if (IS_ERR(link)) {
 		err = PTR_ERR(link);