[PATCH v3 bpf-next] libbpf: add bpf object kern_version attribute setter

[Rafael David Tinoco <rafaeldtinoco@ubuntu.com>]

Unfortunately some distros don't have their kernel version defined
accurately in <linux/version.h> due to different long term support
reasons.

It is important to have a way to override the bpf kern_version
attribute during runtime: some old kernels might still check for
kern_version attribute during bpf_prog_load().

Signed-off-by: Rafael David Tinoco <rafaeldtinoco@ubuntu.com>
---
 tools/lib/bpf/libbpf.c   | 10 ++++++++++
 tools/lib/bpf/libbpf.h   |  1 +
 tools/lib/bpf/libbpf.map |  1 +
 3 files changed, 12 insertions(+)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 058b643cbcb1..3ac3d8dced7f 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -8269,6 +8269,16 @@ int bpf_object__btf_fd(const struct bpf_object *obj)
 	return obj->btf ? btf__fd(obj->btf) : -1;
 }
 
+int bpf_object__set_kversion(struct bpf_object *obj, __u32 kern_version)
+{
+	if (obj->loaded)
+		return -EINVAL;
+
+	obj->kern_version = kern_version;
+
+	return 0;
+}
+
 int bpf_object__set_priv(struct bpf_object *obj, void *priv,
 			 bpf_object_clear_priv_t clear_priv)
 {
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index a1a424b9b8ff..cf9bc6f1f925 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -143,6 +143,7 @@ LIBBPF_API int bpf_object__unload(struct bpf_object *obj);
 
 LIBBPF_API const char *bpf_object__name(const struct bpf_object *obj);
 LIBBPF_API unsigned int bpf_object__kversion(const struct bpf_object *obj);
+LIBBPF_API int bpf_object__set_kversion(struct bpf_object *obj, __u32 kern_version);
 
 struct btf;
 LIBBPF_API struct btf *bpf_object__btf(const struct bpf_object *obj);
diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index 279ae861f568..f5990f7208ce 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -359,4 +359,5 @@ LIBBPF_0.4.0 {
 		bpf_linker__finalize;
 		bpf_linker__free;
 		bpf_linker__new;
+		bpf_object__set_kversion;
 } LIBBPF_0.3.0;
-- 
2.27.0