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 +74,12 @@ 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 */
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(4,12,0)
+#define EXTENDED_ACK_REPORTING
+#endif
+
 int export_table = -1, import_tables[MAX_IMPORT_TABLES], import_table_count = 0;
 
 struct sysctl_setting {
@@ -319,10 +326,12 @@ netlink_socket(struct netlink *nl, uint32_t groups)
         }
     }
 
+#ifdef 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)
@@ -344,6 +353,7 @@ netlink_socket(struct netlink *nl, uint32_t groups)
     }
 }
 
+#ifdef EXTENDED_ACK_REPORTING
 #define NLA_OK(nla,len) ((len) >= (int)sizeof(struct nlattr) && \
 			 (nla)->nla_len >= sizeof(struct nlattr) && \
 			 (nla)->nla_len <= (len))
@@ -380,6 +390,7 @@ static int netlink_get_extack(struct nlmsghdr *nh, int len, int done)
 
     return 0;
 }
+#endif
 
 static int
 netlink_read(struct netlink *nl, struct netlink *nl_ignore, int answer,
@@ -467,13 +478,17 @@ netlink_read(struct netlink *nl, struct netlink *nl_ignore, int answer,
                         nh->nlmsg_pid, nl->sockaddr.nl_pid);
                 continue;
             } else if(nh->nlmsg_type == NLMSG_DONE) {
+#ifdef EXTENDED_ACK_REPORTING
                 netlink_get_extack(nh, len, 1);
+#endif
                 kdebugf("(done)\n");
                 done = 1;
                 break;
             } else if(nh->nlmsg_type == NLMSG_ERROR) {
                 struct nlmsgerr *err = (struct nlmsgerr *)NLMSG_DATA(nh);
+#ifdef EXTENDED_ACK_REPORTING
                 netlink_get_extack(nh, len, 0);
+#endif
                 if(err->error == 0) {
                     kdebugf("(ACK)\n");
                     return 0;

[Julien Muchembled]

No, detect at run-time rather than at compile-time. There's already a kernel_older_than function that you can use to set a global flag.

[Joanne Hugé]

Compilation fails on OBS for debian 9 because NETLINK_EXT_ACK for example is not defined so this is why I am detecting at compile-time.

[Joanne Hugé]

You mean define the macros that don't exist ? There is NETLINK_EXT_ACK, NLMSGERR_ATTR_MSG and NLM_F_ACK_TLVS, so we could define these three and then detect kernel verison at run-time

[Julien Muchembled]

Ok, this conditionally revert d5369ea2: can you mention this in the commit message ?

I think you can simplify a little in 2 ways:

#define EXTENDED_ACK_REPORTING (LINUX_VERSION_CODE >= KERNEL_VERSION(4,12,0))
...
#if EXTENDED_ACK_REPORTING
...

and have an empty netlink_get_extack when < 4.2:

static int netlink_get_extack(struct nlmsghdr *nh, int len, int done)
{
#if EXTENDED_ACK_REPORTING
...
#endif
    return 0;
}