[PATCH 2/3] libbpf: Add helper to extract perf fd from bpf_link

[Daniel Xu <dxu@dxuuu.xyz>]

It is sometimes necessary to perform ioctl's on the underlying perf fd.
There is not currently a way to extract the fd given a bpf_link, so add a
helper for it.
---
 tools/lib/bpf/libbpf.c   | 13 +++++++++++++
 tools/lib/bpf/libbpf.h   |  1 +
 tools/lib/bpf/libbpf.map |  5 +++++
 3 files changed, 19 insertions(+)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index ead915aec349..8469d69448ae 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -4004,6 +4004,19 @@ static int bpf_link__destroy_perf_event(struct bpf_link *link)
 	return err;
 }
 
+int bpf_link__get_perf_fd(struct bpf_link *link)
+{
+	struct bpf_link_fd *l = (void *)link;
+
+	if (!link)
+		return -1;
+
+	if (link->destroy != &bpf_link__destroy_perf_event)
+		return -1;
+
+	return l->fd;
+}
+
 struct bpf_link *bpf_program__attach_perf_event(struct bpf_program *prog,
 						int pfd)
 {
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index 8a9d462a6f6d..5391ac95e4fa 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -168,6 +168,7 @@ LIBBPF_API void bpf_program__unload(struct bpf_program *prog);
 struct bpf_link;
 
 LIBBPF_API int bpf_link__destroy(struct bpf_link *link);
+LIBBPF_API int bpf_link__get_perf_fd(struct bpf_link *link);
 
 LIBBPF_API struct bpf_link *
 bpf_program__attach_perf_event(struct bpf_program *prog, int pfd);
diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index f9d316e873d8..0f844ce29b04 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -184,3 +184,8 @@ LIBBPF_0.0.4 {
 		perf_buffer__new_raw;
 		perf_buffer__poll;
 } LIBBPF_0.0.3;
+
+LIBBPF_0.0.5 {
+	global:
+		bpf_link__get_perf_fd;
+} LIBBPF_0.0.4;
-- 
2.20.1