[RFC PATCH bpf-next v4 05/12] libbpf: introduce bpf_map__attach_struct_ops_opts()

[Hui Zhu <hui.zhu@linux.dev>]

From: Roman Gushchin <roman.gushchin@linux.dev>

Introduce bpf_map__attach_struct_ops_opts(), an extended version of
bpf_map__attach_struct_ops(), which takes additional struct
bpf_struct_ops_opts argument.

struct bpf_struct_ops_opts has the relative_fd member, which allows
to pass an additional file descriptor argument. It can be used to
attach struct ops maps to cgroups.

Signed-off-by: Roman Gushchin <roman.gushchin@linux.dev>
---
 tools/lib/bpf/bpf.c      |  8 ++++++++
 tools/lib/bpf/libbpf.c   | 18 ++++++++++++++++--
 tools/lib/bpf/libbpf.h   | 14 ++++++++++++++
 tools/lib/bpf/libbpf.map |  1 +
 4 files changed, 39 insertions(+), 2 deletions(-)

diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
index 5846de364209..84a53c594f48 100644
--- a/tools/lib/bpf/bpf.c
+++ b/tools/lib/bpf/bpf.c
@@ -884,6 +884,14 @@ int bpf_link_create(int prog_fd, int target_fd,
 		if (!OPTS_ZEROED(opts, cgroup))
 			return libbpf_err(-EINVAL);
 		break;
+	case BPF_STRUCT_OPS:
+		relative_fd = OPTS_GET(opts, cgroup.relative_fd, 0);
+		attr.link_create.cgroup.relative_fd = relative_fd;
+		attr.link_create.cgroup.expected_revision =
+			OPTS_GET(opts, cgroup.expected_revision, 0);
+		if (!OPTS_ZEROED(opts, cgroup))
+			return libbpf_err(-EINVAL);
+		break;
 	default:
 		if (!OPTS_ZEROED(opts, flags))
 			return libbpf_err(-EINVAL);
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 0c8bf0b5cce4..70a00da54ff5 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -13462,12 +13462,19 @@ static int bpf_link__detach_struct_ops(struct bpf_link *link)
 	return close(link->fd);
 }
 
-struct bpf_link *bpf_map__attach_struct_ops(const struct bpf_map *map)
+struct bpf_link *bpf_map__attach_struct_ops_opts(const struct bpf_map *map,
+						 const struct bpf_struct_ops_opts *opts)
 {
+	DECLARE_LIBBPF_OPTS(bpf_link_create_opts, link_opts);
 	struct bpf_link_struct_ops *link;
 	__u32 zero = 0;
 	int err, fd;
 
+	if (!OPTS_VALID(opts, bpf_struct_ops_opts)) {
+		pr_warn("map '%s': invalid opts\n", map->name);
+		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);
@@ -13503,7 +13510,9 @@ 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_opts.cgroup.relative_fd = OPTS_GET(opts, relative_fd, 0);
+
+	fd = bpf_link_create(map->fd, 0, BPF_STRUCT_OPS, &link_opts);
 	if (fd < 0) {
 		free(link);
 		return libbpf_err_ptr(fd);
@@ -13515,6 +13524,11 @@ struct bpf_link *bpf_map__attach_struct_ops(const struct bpf_map *map)
 	return &link->link;
 }
 
+struct bpf_link *bpf_map__attach_struct_ops(const struct bpf_map *map)
+{
+	return bpf_map__attach_struct_ops_opts(map, NULL);
+}
+
 /*
  * Swap the back struct_ops of a link with a new struct_ops map.
  */
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index dfc37a615578..5aef44bcfcc2 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -920,6 +920,20 @@ bpf_program__attach_cgroup_opts(const struct bpf_program *prog, int cgroup_fd,
 struct bpf_map;
 
 LIBBPF_API struct bpf_link *bpf_map__attach_struct_ops(const struct bpf_map *map);
+
+struct bpf_struct_ops_opts {
+	/* size of this struct, for forward/backward compatibility */
+	size_t sz;
+	__u32 flags;
+	__u32 relative_fd;
+	__u64 expected_revision;
+	size_t :0;
+};
+#define bpf_struct_ops_opts__last_field expected_revision
+
+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 int bpf_link__update_map(struct bpf_link *link, const struct bpf_map *map);
 
 struct bpf_iter_attach_opts {
diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index d18fbcea7578..4779190c97b6 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -454,4 +454,5 @@ LIBBPF_1.7.0 {
 		bpf_prog_assoc_struct_ops;
 		bpf_program__assoc_struct_ops;
 		btf__permute;
+		bpf_map__attach_struct_ops_opts;
 } LIBBPF_1.6.0;
-- 
2.43.0