[RFC PATCH bpf-next 3/9] libbpf: Add support for rstat progs and links

[Yosry Ahmed <yosryahmed@google.com>]

Add support to attach "cgroup_subsys/rstat" programs to a subsystem by
calling bpf_program__attach_subsys. Currently, only CGROUP_SUBSYS_RSTAT
programs are supported for attachment to subsystems.

Signed-off-by: Yosry Ahmed <yosryahmed@google.com>
---
 tools/lib/bpf/bpf.c      |  3 +++
 tools/lib/bpf/bpf.h      |  3 +++
 tools/lib/bpf/libbpf.c   | 35 +++++++++++++++++++++++++++++++++++
 tools/lib/bpf/libbpf.h   |  3 +++
 tools/lib/bpf/libbpf.map |  1 +
 5 files changed, 45 insertions(+)

diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
index cf27251adb92..abfff17cfa07 100644
--- a/tools/lib/bpf/bpf.c
+++ b/tools/lib/bpf/bpf.c
@@ -863,6 +863,9 @@ int bpf_link_create(int prog_fd, int target_fd,
 		if (!OPTS_ZEROED(opts, kprobe_multi))
 			return libbpf_err(-EINVAL);
 		break;
+	case BPF_CGROUP_SUBSYS_RSTAT:
+		attr.link_create.cgroup_subsys.name = ptr_to_u64(OPTS_GET(opts, cgroup_subsys.name, 0));
+		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 f4b4afb6d4ba..384767a9ffd3 100644
--- a/tools/lib/bpf/bpf.h
+++ b/tools/lib/bpf/bpf.h
@@ -413,6 +413,9 @@ struct bpf_link_create_opts {
 		struct {
 			__u64 bpf_cookie;
 		} perf_event;
+		struct {
+			const char *name;
+		} cgroup_subsys;
 		struct {
 			__u32 flags;
 			__u32 cnt;
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 809fe209cdcc..56380953df55 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -8715,6 +8715,7 @@ static const struct bpf_sec_def section_defs[] = {
 	SEC_DEF("cgroup/setsockopt",	CGROUP_SOCKOPT, BPF_CGROUP_SETSOCKOPT, SEC_ATTACHABLE | SEC_SLOPPY_PFX),
 	SEC_DEF("struct_ops+",		STRUCT_OPS, 0, SEC_NONE),
 	SEC_DEF("sk_lookup",		SK_LOOKUP, BPF_SK_LOOKUP, SEC_ATTACHABLE | SEC_SLOPPY_PFX),
+	SEC_DEF("cgroup_subsys/rstat",	CGROUP_SUBSYS_RSTAT, 0, SEC_NONE),
 };
 
 static size_t custom_sec_def_cnt;
@@ -10957,6 +10958,40 @@ static int attach_iter(const struct bpf_program *prog, long cookie, struct bpf_l
 	return libbpf_get_error(*link);
 }
 
+struct bpf_link *bpf_program__attach_subsys(const struct bpf_program *prog,
+					     const char *subsys_name)
+{
+	DECLARE_LIBBPF_OPTS(bpf_link_create_opts, lopts,
+			    .cgroup_subsys.name = subsys_name);
+	struct bpf_link *link = NULL;
+	char errmsg[STRERR_BUFSIZE];
+	int err, prog_fd, link_fd;
+
+	prog_fd = bpf_program__fd(prog);
+	if (prog_fd < 0) {
+		pr_warn("prog '%s': can't attach before loaded\n", prog->name);
+		return libbpf_err_ptr(-EINVAL);
+	}
+
+	link = calloc(1, sizeof(*link));
+	if (!link)
+		return libbpf_err_ptr(-ENOMEM);
+	link->detach = &bpf_link__detach_fd;
+
+	link_fd = bpf_link_create(prog_fd, 0, BPF_CGROUP_SUBSYS_RSTAT, &lopts);
+	if (link_fd < 0) {
+		err = -errno;
+		pr_warn("prog '%s': failed to attach: %s\n",
+			prog->name, libbpf_strerror_r(err, errmsg,
+						      sizeof(errmsg)));
+		free(link);
+		return libbpf_err_ptr(err);
+	}
+
+	link->fd = link_fd;
+	return link;
+}
+
 struct bpf_link *bpf_program__attach(const struct bpf_program *prog)
 {
 	struct bpf_link *link = NULL;
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index 05dde85e19a6..eddbffcd39f7 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -537,6 +537,9 @@ bpf_program__attach_xdp(const struct bpf_program *prog, int ifindex);
 LIBBPF_API struct bpf_link *
 bpf_program__attach_freplace(const struct bpf_program *prog,
 			     int target_fd, const char *attach_func_name);
+LIBBPF_API struct bpf_link *
+bpf_program__attach_subsys(const struct bpf_program *prog,
+			   const char *subsys_name);
 
 struct bpf_map;
 
diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index dd35ee58bfaa..5583a2dbfb7c 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -447,4 +447,5 @@ LIBBPF_0.8.0 {
 		libbpf_register_prog_handler;
 		libbpf_unregister_prog_handler;
 		bpf_program__attach_kprobe_multi_opts;
+		bpf_program__attach_subsys;
 } LIBBPF_0.7.0;
-- 
2.36.0.512.ge40c2bad7a-goog