add helpers to select kernel in some distributions

src/libbpf.c

@@ -777,6 +777,93 @@ bpf_object__add_programs(struct bpf_object *obj, Elf_Data *sec_data,
 	return 0;
 }
 
+static __u32 choose_specific_version0(int fd, __u32 current)
+{
+	char ver[256];
+	__u32 v_major, v_minor, v_patch;
+	ssize_t len = read(fd, ver, sizeof(ver));
+	if (len < 0) {
+		return 0;
+	}
+	ver[len] = '\0';
+
+	char *first = strchr(ver, ' ');
+	if (!first) {
+		return 0;
+	}
+
+	first++;
+	char *version = strchr(first, ' ');
+	if (!version) {
+		return 0;
+	}
+
+	version++;
+	if (sscanf(version, "%u.%u.%u", &v_major, &v_minor, &v_patch) != 3)
+		return current;
+
+	return KERNEL_VERSION(v_major, v_minor, v_patch);
+}
+
+static __u32 choose_kernel_version(__u32 current)
+{
+	FILE *fp_d = fopen("/etc/debian_version","r");
+	int fp_u = open("/proc/version_signature", O_RDONLY);
+	FILE *fp_rh = fopen("/etc/redhat-release","r");
+	char tmp[32];
+	int de = 0;
+	__u32 ret;
+
+	if (!fp_d && !fp_rh && fp_u == -1)
+		return current;
+
+	struct utsname u;
+	uname(&u);
+
+	if (fp_d) {
+		fclose(fp_d);
+		de = 1;
+	}
+
+	if (fp_rh) {
+		fclose(fp_rh);
+		de = 0;
+	}
+
+	if ( fp_u > 0 ) {
+		ret = choose_specific_version0(fp_u, current);
+		close(fp_u);
+		return (!ret)?current:ret;
+	}
+
+	__u32 v_kernel,v_major, v_minor, v_patch;
+	__u32 r_kernel,r_major, r_minor, r_patch;
+
+	if (sscanf(u.release, "%u.%u.%u-%u", &v_kernel, &v_major, &v_minor, &v_patch) != 4)
+		return current;
+
+	int length = snprintf(tmp, 31, "%u.%u", v_kernel, v_major);
+	tmp[length] = '\0';
+
+	char *parse = strstr(u.version, tmp);
+	if (!parse) {
+		return current;
+	}
+
+	char *space = strchr(parse, ' ');
+	if(space) {
+		length = (int)(space - parse);
+		strncpy(tmp, parse, (size_t)length);
+		tmp[length] = '\0';
+	}
+
+	if (sscanf(tmp, "%u.%u.%u-%u", &r_kernel, &r_major, &r_minor, &r_patch) != 4)
+		return current;
+
+	ret = (de)?KERNEL_VERSION(r_kernel, r_major, r_minor):KERNEL_VERSION(r_kernel, r_major, r_minor) + r_patch;
+	return (ret > current)?ret:current;
+}
+
 static __u32 get_kernel_version(void)
 {
 	__u32 major, minor, patch;
@@ -785,7 +872,11 @@ static __u32 get_kernel_version(void)
 	uname(&info);
 	if (sscanf(info.release, "%u.%u.%u", &major, &minor, &patch) != 3)
 		return 0;
-	return KERNEL_VERSION(major, minor, patch);
+
+	if (major < 5)
+		return choose_kernel_version(KERNEL_VERSION(major, minor, patch));
+	else
+		return KERNEL_VERSION(major, minor, patch);
 }
 
 static const struct btf_member *