Compile extended ack reporting only for kernel >= 4.12

kernel_netlink.c

@@ -39,6 +39,7 @@ THE SOFTWARE.
 #include <sys/socket.h>
 #include <linux/netlink.h>
 #include <linux/rtnetlink.h>
+#include <linux/version.h>
 #include <net/if_arp.h>
 
 /* From <linux/if_bridge.h> */
@@ -73,6 +74,10 @@ THE SOFTWARE.
             memcpy(d, RTA_DATA(rta), 16);                               \
     } while(0)
 
+/* extended ACK reporting was introduced in Linux by commit
+   2d4bc93368f5a0ddb57c8c885cdad9c9b7a10ed5 first released as 4.12 */
+#define EXTENDED_ACK_REPORTING (LINUX_VERSION_CODE >= KERNEL_VERSION(4,12,0))
+
 int export_table = -1, import_tables[MAX_IMPORT_TABLES], import_table_count = 0;
 
 struct sysctl_setting {
@@ -319,10 +324,12 @@ netlink_socket(struct netlink *nl, uint32_t groups)
         }
     }
 
+#if EXTENDED_ACK_REPORTING
     rc = setsockopt(nl->sock, SOL_NETLINK, NETLINK_EXT_ACK,
                     &one, sizeof(one));
     if(rc < 0)
         perror("Warning: couldn't enable netlink extended acks");
+#endif
 
     rc = bind(nl->sock, (struct sockaddr *)&nl->sockaddr, nl->socklen);
     if(rc < 0)
@@ -354,6 +361,7 @@ netlink_socket(struct netlink *nl, uint32_t groups)
 
 static int netlink_get_extack(struct nlmsghdr *nh, int len, int done)
 {
+#if EXTENDED_ACK_REPORTING
     const char *msg = NULL;
     struct nlattr *nla;
 
@@ -378,6 +386,7 @@ static int netlink_get_extack(struct nlmsghdr *nh, int len, int done)
     if(msg && *msg != '\0')
         kdebugf(" extack: '%s' ", msg);
 
+#endif
     return 0;
 }