[PATCH v3 bpf-next 2/9] libbpf: introduce concept of bpf_link

[Andrii Nakryiko <andriin@fb.com>]

bpf_link is and abstraction of an association of a BPF program and one
of many possible BPF attachment points (hooks). This allows to have
uniform interface for detaching BPF programs regardless of the nature of
link and how it was created. Details of creation and setting up of
a specific bpf_link is handled by corresponding attachment methods
(bpf_program__attach_xxx) added in subsequent commits. Once successfully
created, bpf_link has to be eventually destroyed with
bpf_link__destroy(), at which point BPF program is disassociated from
a hook and all the relevant resources are freed.

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
---
 tools/lib/bpf/libbpf.c   | 17 +++++++++++++++++
 tools/lib/bpf/libbpf.h   |  4 ++++
 tools/lib/bpf/libbpf.map |  3 ++-
 3 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 6e6ebef11ba3..455795e6f8af 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -3941,6 +3941,23 @@ int bpf_prog_load_xattr(const struct bpf_prog_load_attr *attr,
 	return 0;
 }
 
+struct bpf_link {
+	int (*destroy)(struct bpf_link *link);
+};
+
+int bpf_link__destroy(struct bpf_link *link)
+{
+	int err;
+
+	if (!link)
+		return 0;
+
+	err = link->destroy(link);
+	free(link);
+
+	return err;
+}
+
 enum bpf_perf_event_ret
 bpf_perf_event_read_simple(void *mmap_mem, size_t mmap_size, size_t page_size,
 			   void **copy_mem, size_t *copy_size,
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index d639f47e3110..5082a5ebb0c2 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -165,6 +165,10 @@ LIBBPF_API int bpf_program__pin(struct bpf_program *prog, const char *path);
 LIBBPF_API int bpf_program__unpin(struct bpf_program *prog, const char *path);
 LIBBPF_API void bpf_program__unload(struct bpf_program *prog);
 
+struct bpf_link;
+
+LIBBPF_API int bpf_link__destroy(struct bpf_link *link);
+
 struct bpf_insn;
 
 /*
diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index 2c6d835620d2..3cde850fc8da 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -167,10 +167,11 @@ LIBBPF_0.0.3 {
 
 LIBBPF_0.0.4 {
 	global:
+		bpf_link__destroy;
+		bpf_object__load_xattr;
 		btf_dump__dump_type;
 		btf_dump__free;
 		btf_dump__new;
 		btf__parse_elf;
-		bpf_object__load_xattr;
 		libbpf_num_possible_cpus;
 } LIBBPF_0.0.3;
-- 
2.17.1