libbpf: Add bpf object kern_version attribute setter

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>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20210323040952.2118241-1-rafaeldtinoco@ubuntu.com

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 10a0a67..cebb0e8 100644 (file)
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -8270,6 +8270,16 @@ 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 89ade7d..f500621 100644 (file)
--- 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 279ae86..f5990f7 100644 (file)
--- 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;