[PATCH bpf-next v2 7/9] libbpf: don't free btf if program of multi-link tracing existing

[Menglong Dong]

By default, the kernel btf that we load during loading program will be
freed after the programs are loaded in bpf_object_load(). However, we
still need to use these btf for tracing of multi-link during attaching.
Therefore, we don't free the btfs until the bpf object is closed if any
bpf programs of the type multi-link tracing exist.

Meanwhile, introduce the new api bpf_object__free_btf() to manually free
the btfs after attaching.

Signed-off-by: Menglong Dong <dongmenglong.8 at bytedance.com>
---
 tools/lib/bpf/libbpf.c   | 47 ++++++++++++++++++++++++++++++----------
 tools/lib/bpf/libbpf.h   |  2 ++
 tools/lib/bpf/libbpf.map |  1 +
 3 files changed, 38 insertions(+), 12 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 567ad367e7aa..fd5428494a7e 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -8267,6 +8267,39 @@ static int bpf_object_prepare_struct_ops(struct bpf_object *obj)
 	return 0;
 }
 
+void bpf_object__free_btfs(struct bpf_object *obj)
+{
+	int i;
+
+	/* clean up module BTFs */
+	for (i = 0; i < obj->btf_module_cnt; i++) {
+		close(obj->btf_modules[i].fd);
+		btf__free(obj->btf_modules[i].btf);
+		free(obj->btf_modules[i].name);
+	}
+	free(obj->btf_modules);
+	obj->btf_modules = NULL;
+	obj->btf_module_cnt = 0;
+
+	/* clean up vmlinux BTF */
+	btf__free(obj->btf_vmlinux);
+	obj->btf_vmlinux = NULL;
+}
+
+static void bpf_object_early_free_btf(struct bpf_object *obj)
+{
+	struct bpf_program *prog;
+
+	bpf_object__for_each_program(prog, obj) {
+		if (prog->expected_attach_type == BPF_TRACE_FENTRY_MULTI ||
+		    prog->expected_attach_type == BPF_TRACE_FEXIT_MULTI ||
+		    prog->expected_attach_type == BPF_MODIFY_RETURN_MULTI)
+			return;
+	}
+
+	bpf_object__free_btfs(obj);
+}
+
 static int bpf_object_load(struct bpf_object *obj, int extra_log_level, const char *target_btf_path)
 {
 	int err, i;
@@ -8307,18 +8340,7 @@ static int bpf_object_load(struct bpf_object *obj, int extra_log_level, const ch
 	/* clean up fd_array */
 	zfree(&obj->fd_array);
 
-	/* clean up module BTFs */
-	for (i = 0; i < obj->btf_module_cnt; i++) {
-		close(obj->btf_modules[i].fd);
-		btf__free(obj->btf_modules[i].btf);
-		free(obj->btf_modules[i].name);
-	}
-	free(obj->btf_modules);
-
-	/* clean up vmlinux BTF */
-	btf__free(obj->btf_vmlinux);
-	obj->btf_vmlinux = NULL;
-
+	bpf_object_early_free_btf(obj);
 	obj->loaded = true; /* doesn't matter if successfully or not */
 
 	if (err)
@@ -8791,6 +8813,7 @@ void bpf_object__close(struct bpf_object *obj)
 	usdt_manager_free(obj->usdt_man);
 	obj->usdt_man = NULL;
 
+	bpf_object__free_btfs(obj);
 	bpf_gen__free(obj->gen_loader);
 	bpf_object__elf_finish(obj);
 	bpf_object_unload(obj);
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index 5723cbbfcc41..c41a909ea4c1 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -299,6 +299,8 @@ LIBBPF_API struct bpf_program *
 bpf_object__find_program_by_name(const struct bpf_object *obj,
 				 const char *name);
 
+LIBBPF_API void bpf_object__free_btfs(struct bpf_object *obj);
+
 LIBBPF_API int
 libbpf_prog_type_by_name(const char *name, enum bpf_prog_type *prog_type,
 			 enum bpf_attach_type *expected_attach_type);
diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index 86804fd90dd1..57642b78917f 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -413,4 +413,5 @@ LIBBPF_1.4.0 {
 		bpf_token_create;
 		btf__new_split;
 		btf_ext__raw_data;
+		bpf_object__free_btfs;
 } LIBBPF_1.3.0;
-- 
2.39.2