On Thu, 2004-07-29 at 09:16, Jamal Hadi Salim wrote:

On Tue, 2004-07-27 at 12:50, Stephen Hemminger wrote:

quoted

@@ -404,13 +402,8 @@
 		return -1;
 	}
 
-	if (kind != 2) {
-		if (rtnl_exlock_nowait()) {
-			*errp = 0;
-			return -1;
-		}
+	if (kind != 2) 
 		exclusive = 1;
-	}
 
 	memset(&rta, 0, sizeof(rta));
 

@@ -439,14 +432,10 @@
 		goto err_inval;
 	err = link->doit(skb, nlh, (void *)&rta);
 
-	if (exclusive)
-		rtnl_exunlock();
 	*errp = err;
 	return err;
 
 err_inval:
-	if (exclusive)
-		rtnl_exunlock();
 	*errp = -EINVAL;
 	return -1;
 }

This piece is the only one i would worry about.
I dont remember the historical reasoning for rtnl_ex* I know its not
useful as is right now. OTOH, if it was useful then the above code would
have meant something. Dave/Alexey?

I think i may have figured it out.
The rtnl_ex* seems to have been intended as more fine grain exclusive
writer locking to the ->doit() functions which do make modifications to
data. In other words if there are several rtnetlink sockets trying to
modify the routing table, this would act as a serialization point.

At the moment, the RTNL_SEM (grabbed around rtnetlink_rcv() 
viartnl_shlock_nowait ) seems to protect on this but its too 
fat a lock. So at some point we may need to clean it.

Before you take my word on it, lets wait to hear from Alexey/Dave.

cheers,
jamal