IPv6 - support for NLM_F_* flags at IPv6 routing requests

The support for NLM_F_* flags at IPv6 routing requests.

If NLM_F_CREATE flag is not defined for RTM_NEWROUTE request, warning is printed, but no error is returned. Instead new route is added.

Exception is when NLM_F_REPLACE flag is given without NLM_F_CREATE, and no matching route is found. In this case it should be safe to assume that the request issuer is familiar with NLM_F_* flags, and does really not want route to be created.

Specifying NLM_F_REPLACE flag will now make the kernel to search for matching route, and replace it with new one. If no route is found and NLM_F_CREATE is specified as well, then new route is created.

Also, specifying NLM_F_EXCL will yield returning of error if matching route is found.

Patch is created against linux-3.1-rc4

diff -uNr linux-3.1-rc4.orig/net/ipv6/route.c linux-3.1-rc4.new/net/ipv6/route.c
@@ -1223,9 +1223,18 @@
 	if (cfg->fc_metric == 0)
 		cfg->fc_metric = IP6_RT_PRIO_USER;
 
-	table = fib6_new_table(net, cfg->fc_table);
+	err = -ENOBUFS;
+	if (NULL != cfg->fc_nlinfo.nlh &&
+	    !(cfg->fc_nlinfo.nlh->nlmsg_flags&NLM_F_CREATE)) {
+		table = fib6_get_table(net, cfg->fc_table);
+		if (table == NULL) {
+			printk(KERN_WARNING "NLM_F_CREATE should be specified when creating new rt\n");
+			table = fib6_new_table(net, cfg->fc_table);
+		}
+	} else {
+		table = fib6_new_table(net, cfg->fc_table);
+	}
 	if (table == NULL) {
-		err = -ENOBUFS;
 		goto out;
 	}