check return value of rtnl_send and related functions

Use warn_unused_result to enforce checking return value of rtnl_send,
and fix where the errors are.

Suggested by initial patch from Petr Písař <ppisar@redhat.com>

include/libnetlink.h

@@ -22,13 +22,22 @@ struct rtnl_handle
 
 extern int rcvbuf;
 
-extern int rtnl_open(struct rtnl_handle *rth, unsigned subscriptions);
-extern int rtnl_open_byproto(struct rtnl_handle *rth, unsigned subscriptions, int protocol);
+extern int rtnl_open(struct rtnl_handle *rth, unsigned subscriptions)
+	__attribute__((warn_unused_result));
+
+extern int rtnl_open_byproto(struct rtnl_handle *rth, unsigned subscriptions,
+			     int protocol)
+	__attribute__((warn_unused_result));
+
 extern void rtnl_close(struct rtnl_handle *rth);
-extern int rtnl_wilddump_request(struct rtnl_handle *rth, int fam, int type);
+extern int rtnl_wilddump_request(struct rtnl_handle *rth, int fam, int type)
+	__attribute__((warn_unused_result));
 extern int rtnl_wilddump_req_filter(struct rtnl_handle *rth, int fam, int type,
-				    __u32 filt_mask);
-extern int rtnl_dump_request(struct rtnl_handle *rth, int type, void *req, int len);
+				    __u32 filt_mask)
+	__attribute__((warn_unused_result));
+extern int rtnl_dump_request(struct rtnl_handle *rth, int type, void *req,
+			     int len)
+	__attribute__((warn_unused_result));
 
 typedef int (*rtnl_filter_t)(const struct sockaddr_nl *,
 			     struct nlmsghdr *n, void *);
@@ -44,9 +53,12 @@ extern int rtnl_dump_filter_l(struct rtnl_handle *rth,
 extern int rtnl_dump_filter(struct rtnl_handle *rth, rtnl_filter_t filter,
 			    void *arg);
 extern int rtnl_talk(struct rtnl_handle *rtnl, struct nlmsghdr *n, pid_t peer,
-		     unsigned groups, struct nlmsghdr *answer);
-extern int rtnl_send(struct rtnl_handle *rth, const void *buf, int);
-extern int rtnl_send_check(struct rtnl_handle *rth, const void *buf, int);
+		     unsigned groups, struct nlmsghdr *answer)
+	__attribute__((warn_unused_result));
+extern int rtnl_send(struct rtnl_handle *rth, const void *buf, int)
+	__attribute__((warn_unused_result));
+extern int rtnl_send_check(struct rtnl_handle *rth, const void *buf, int)
+	__attribute__((warn_unused_result));
 
 extern int addattr(struct nlmsghdr *n, int maxlen, int type);
 extern int addattr8(struct nlmsghdr *n, int maxlen, int type, __u8 data);

ip/iplink.c

@@ -178,7 +178,10 @@ static int iplink_have_newlink(void)
 		req.n.nlmsg_type = RTM_NEWLINK;
 		req.i.ifi_family = AF_UNSPEC;
 
-		rtnl_send(&rth, &req.n, req.n.nlmsg_len);
+		if (rtnl_send(&rth, &req.n, req.n.nlmsg_len) < 0) {
+			perror("request send failed");
+			exit(1);
+		}
 		rtnl_listen(&rth, accept_msg, NULL);
 	}
 	return have_rtnl_newlink;

ip/ipnetconf.c

@@ -161,7 +161,10 @@ static int do_show(int argc, char **argv)
 			addattr_l(&req.n, sizeof(req), NETCONFA_IFINDEX,
 				  &filter.ifindex, sizeof(filter.ifindex));
 
-		rtnl_send(&rth, &req.n, req.n.nlmsg_len);
+		if (rtnl_send(&rth, &req.n, req.n.nlmsg_len) < 0) {
+			perror("Can not send request");
+			exit(1);
+		}
 		rtnl_listen(&rth, print_netconf, stdout);
 	} else {
 dump:

misc/arpd.c

@@ -428,7 +428,11 @@ static int do_one_request(struct nlmsghdr *n)
 
 static void load_initial_table(void)
 {
-	rtnl_wilddump_request(&rth, AF_INET, RTM_GETNEIGH);
+	if (rtnl_wilddump_request(&rth, AF_INET, RTM_GETNEIGH) < 0) {
+		perror("dump request failed");
+		exit(1);
+	}
+		
 }
 
 static void get_kern_msg(void)

misc/ss.c

@@ -996,7 +996,9 @@ static int xll_initted = 0;
 static void xll_init(void)
 {
 	struct rtnl_handle rth;
-	rtnl_open(&rth, 0);
+	if (rtnl_open(&rth, 0) < 0)
+		exit(1);
+
 	ll_init_map(&rth);
 	rtnl_close(&rth);
 	xll_initted = 1;