libbpf: Add runtime APIs to query libbpf version

Libbpf provided LIBBPF_MAJOR_VERSION and LIBBPF_MINOR_VERSION macros to
check libbpf version at compilation time. This doesn't cover all the
needs, though, because version of libbpf that application is compiled
against doesn't necessarily match the version of libbpf at runtime,
especially if libbpf is used as a shared library.

Add libbpf_major_version() and libbpf_minor_version() returning major
and minor versions, respectively, as integers. Also add a convenience
libbpf_version_string() for various tooling using libbpf to print out
libbpf version in a human-readable form. Currently it will return
"v0.6", but in the future it can contains some extra information, so the
format itself is not part of a stable API and shouldn't be relied upon.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Toke Høiland-Jørgensen <toke@redhat.com>
Link: https://lore.kernel.org/bpf/20211118174054.2699477-1-andrii@kernel.org

tools/lib/bpf/libbpf.c

@@ -168,6 +168,25 @@ int libbpf_set_strict_mode(enum libbpf_strict_mode mode)
 	return 0;
 }
 
+__u32 libbpf_major_version(void)
+{
+	return LIBBPF_MAJOR_VERSION;
+}
+
+__u32 libbpf_minor_version(void)
+{
+	return LIBBPF_MINOR_VERSION;
+}
+
+const char *libbpf_version_string(void)
+{
+#define __S(X) #X
+#define _S(X) __S(X)
+	return  "v" _S(LIBBPF_MAJOR_VERSION) "." _S(LIBBPF_MINOR_VERSION);
+#undef _S
+#undef __S
+}
+
 enum kern_feature_id {
 	/* v4.14: kernel support for program & map names. */
 	FEAT_PROG_NAME,

tools/lib/bpf/libbpf.h

@@ -24,6 +24,10 @@
 extern "C" {
 #endif
 
+LIBBPF_API __u32 libbpf_major_version(void);
+LIBBPF_API __u32 libbpf_minor_version(void);
+LIBBPF_API const char *libbpf_version_string(void);
+
 enum libbpf_errno {
 	__LIBBPF_ERRNO__START = 4000,
 

tools/lib/bpf/libbpf.map

@@ -410,6 +410,9 @@ LIBBPF_0.6.0 {
 		btf__type_cnt;
 		btf_dump__new;
 		btf_dump__new_deprecated;
+		libbpf_major_version;
+		libbpf_minor_version;
+		libbpf_version_string;
 		perf_buffer__new;
 		perf_buffer__new_deprecated;
 		perf_buffer__new_raw;