netlink: make nlmsg_end() and genlmsg_end() void

Contrary to common expectations for an "int" return, these functions
return only a positive value -- if used correctly they cannot even
return 0 because the message header will necessarily be in the skb.

This makes the very common pattern of

  if (genlmsg_end(...) < 0) { ... }

be a whole bunch of dead code. Many places also simply do

  return nlmsg_end(...);

and the caller is expected to deal with it.

This also commonly (at least for me) causes errors, because it is very
common to write

  if (my_function(...))
    /* error condition */

and if my_function() does "return nlmsg_end()" this is of course wrong.

Additionally, there's not a single place in the kernel that actually
needs the message length returned, and if anyone needs it later then
it'll be very easy to just use skb->len there.

Remove this, and make the functions void. This removes a bunch of dead
code as described above. The patch adds lines because I did

-	return nlmsg_end(...);
+	nlmsg_end(...);
+	return 0;

I could have preserved all the function's return values by returning
skb->len, but instead I've audited all the places calling the affected
functions and found that none cared. A few places actually compared
the return value with <= 0 in dump functionality, but that could just
be changed to < 0 with no change in behaviour, so I opted for the more
efficient version.

One instance of the error I've made numerous times now is also present
in net/phonet/pn_netlink.c in the route_dumpit() function - it didn't
check for <0 or <=0 and thus broke out of the loop every single time.
I've preserved this since it will (I think) have caused the messages to
userspace to be formatted differently with just a single message for
every SKB returned to userspace. It's possible that this isn't needed
for the tools that actually use this, but I don't even know what they
are so couldn't test that changing this behaviour would be acceptable.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/netlabel/netlabel_cipso_v4.c

@@ -641,7 +641,8 @@ static int netlbl_cipsov4_listall_cb(struct cipso_v4_doi *doi_def, void *arg)
 	if (ret_val != 0)
 		goto listall_cb_failure;
 
-	return genlmsg_end(cb_arg->skb, data);
+	genlmsg_end(cb_arg->skb, data);
+	return 0;
 
 listall_cb_failure:
 	genlmsg_cancel(cb_arg->skb, data);

net/netlabel/netlabel_mgmt.c

@@ -456,7 +456,8 @@ static int netlbl_mgmt_listall_cb(struct netlbl_dom_map *entry, void *arg)
 		goto listall_cb_failure;
 
 	cb_arg->seq++;
-	return genlmsg_end(cb_arg->skb, data);
+	genlmsg_end(cb_arg->skb, data);
+	return 0;
 
 listall_cb_failure:
 	genlmsg_cancel(cb_arg->skb, data);
@@ -620,7 +621,8 @@ static int netlbl_mgmt_protocols_cb(struct sk_buff *skb,
 	if (ret_val != 0)
 		goto protocols_cb_failure;
 
-	return genlmsg_end(skb, data);
+	genlmsg_end(skb, data);
+	return 0;
 
 protocols_cb_failure:
 	genlmsg_cancel(skb, data);

net/netlabel/netlabel_unlabeled.c

@@ -1163,7 +1163,8 @@ static int netlbl_unlabel_staticlist_gen(u32 cmd,
 		goto list_cb_failure;
 
 	cb_arg->seq++;
-	return genlmsg_end(cb_arg->skb, data);
+	genlmsg_end(cb_arg->skb, data);
+	return 0;
 
 list_cb_failure:
 	genlmsg_cancel(cb_arg->skb, data);