[RFC bpf-next v1 3/4] libbpf: Support link-based struct_ops attach with options

[Amery Hung <ameryhung@xxxxxxxxx>]

Currently libbpf supports bpf_map__attach_struct_ops() with signature:
  LIBBPF_API struct bpf_link *
  bpf_map__attach_struct_ops(const struct bpf_map *map);

To support cookie for struct_ops attachment, an additional argument is
needed. The argument is a pointer to a structure containing all the
option used for bpf_link_create.

Add the new API:
  LIBBPF_API struct bpf_link *
  bpf_map__attach_struct_ops_opts(const struct bpf_map *map,
                                  const struct bpf_struct_ops_opts *opts);

Signed-off-by: Amery Hung <ameryhung@xxxxxxxxx>
---
 tools/lib/bpf/bpf.c      |  5 +++++
 tools/lib/bpf/bpf.h      |  3 +++
 tools/lib/bpf/libbpf.c   | 14 +++++++++++++-
 tools/lib/bpf/libbpf.h   | 10 ++++++++++
 tools/lib/bpf/libbpf.map |  1 +
 5 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
index ab40dbf9f020..c1e66e190982 100644
--- a/tools/lib/bpf/bpf.c
+++ b/tools/lib/bpf/bpf.c
@@ -881,6 +881,11 @@ int bpf_link_create(int prog_fd, int target_fd,
 		if (!OPTS_ZEROED(opts, cgroup))
 			return libbpf_err(-EINVAL);
 		break;
+	case BPF_STRUCT_OPS:
+		attr.link_create.struct_ops.cookie = OPTS_GET(opts, struct_ops.cookie, 0);
+		if (!OPTS_ZEROED(opts, struct_ops))
+			return libbpf_err(-EINVAL);
+		break;
 	default:
 		if (!OPTS_ZEROED(opts, flags))
 			return libbpf_err(-EINVAL);
diff --git a/tools/lib/bpf/bpf.h b/tools/lib/bpf/bpf.h
index 7252150e7ad3..2386ad4a295c 100644
--- a/tools/lib/bpf/bpf.h
+++ b/tools/lib/bpf/bpf.h
@@ -443,6 +443,9 @@ struct bpf_link_create_opts {
 			__u32 relative_id;
 			__u64 expected_revision;
 		} cgroup;
+		struct {
+			__u64 cookie;
+		} struct_ops;
 	};
 	size_t :0;
 };
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index aee36402f0a3..f5b71eccd5cc 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -13110,10 +13110,20 @@ static int bpf_link__detach_struct_ops(struct bpf_link *link)
 
 struct bpf_link *bpf_map__attach_struct_ops(const struct bpf_map *map)
 {
+	return bpf_map__attach_struct_ops_opts(map, NULL);
+}
+
+struct bpf_link *bpf_map__attach_struct_ops_opts(const struct bpf_map *map,
+						 const struct bpf_struct_ops_opts *opts)
+{
+	LIBBPF_OPTS(bpf_link_create_opts, link_create_opts);
 	struct bpf_link_struct_ops *link;
 	__u32 zero = 0;
 	int err, fd;
 
+	if (!OPTS_VALID(opts, bpf_struct_ops_opts))
+		return libbpf_err_ptr(-EINVAL);
+
 	if (!bpf_map__is_struct_ops(map)) {
 		pr_warn("map '%s': can't attach non-struct_ops map\n", map->name);
 		return libbpf_err_ptr(-EINVAL);
@@ -13149,7 +13159,9 @@ struct bpf_link *bpf_map__attach_struct_ops(const struct bpf_map *map)
 		return &link->link;
 	}
 
-	fd = bpf_link_create(map->fd, 0, BPF_STRUCT_OPS, NULL);
+	link_create_opts.struct_ops.cookie = OPTS_GET(opts, cookie, 0);
+
+	fd = bpf_link_create(map->fd, 0, BPF_STRUCT_OPS, &link_create_opts);
 	if (fd < 0) {
 		free(link);
 		return libbpf_err_ptr(fd);
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index d1cf813a057b..a4a758a8a25b 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -894,6 +894,16 @@ bpf_program__attach_cgroup_opts(const struct bpf_program *prog, int cgroup_fd,
 
 struct bpf_map;
 
+struct bpf_struct_ops_opts {
+	/* size of this struct, for forward/backward compatibility */
+	size_t sz;
+	__u64 cookie;
+	size_t :0;
+};
+#define bpf_struct_ops_opts__last_field cookie
+
+LIBBPF_API struct bpf_link *bpf_map__attach_struct_ops_opts(const struct bpf_map *map,
+							    const struct bpf_struct_ops_opts* opts);
 LIBBPF_API struct bpf_link *bpf_map__attach_struct_ops(const struct bpf_map *map);
 LIBBPF_API int bpf_link__update_map(struct bpf_link *link, const struct bpf_map *map);
 
diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index 1bbf77326420..6998300c766a 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -439,6 +439,7 @@ LIBBPF_1.6.0 {
 		bpf_object__prepare;
 		bpf_prog_stream_read;
 		bpf_program__attach_cgroup_opts;
+		bpf_map__attach_struct_ops_opts;
 		bpf_program__func_info;
 		bpf_program__func_info_cnt;
 		bpf_program__line_info;
-- 
2.47.1