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/wireless/nl80211.c

@@ -1721,7 +1721,8 @@ static int nl80211_send_wiphy(struct cfg80211_registered_device *rdev,
 		break;
 	}
  finish:
-	return genlmsg_end(msg, hdr);
+	genlmsg_end(msg, hdr);
+	return 0;
 
  nla_put_failure:
 	genlmsg_cancel(msg, hdr);
@@ -2404,7 +2405,8 @@ static int nl80211_send_iface(struct sk_buff *msg, u32 portid, u32 seq, int flag
 			goto nla_put_failure;
 	}
 
-	return genlmsg_end(msg, hdr);
+	genlmsg_end(msg, hdr);
+	return 0;
 
  nla_put_failure:
 	genlmsg_cancel(msg, hdr);
@@ -3825,7 +3827,8 @@ static int nl80211_send_station(struct sk_buff *msg, u32 cmd, u32 portid,
 		    sinfo->assoc_req_ies))
 		goto nla_put_failure;
 
-	return genlmsg_end(msg, hdr);
+	genlmsg_end(msg, hdr);
+	return 0;
 
  nla_put_failure:
 	genlmsg_cancel(msg, hdr);
@@ -4555,7 +4558,8 @@ static int nl80211_send_mpath(struct sk_buff *msg, u32 portid, u32 seq,
 
 	nla_nest_end(msg, pinfoattr);
 
-	return genlmsg_end(msg, hdr);
+	genlmsg_end(msg, hdr);
+	return 0;
 
  nla_put_failure:
 	genlmsg_cancel(msg, hdr);
@@ -5507,7 +5511,8 @@ static int nl80211_send_regdom(struct sk_buff *msg, struct netlink_callback *cb,
 	    nla_put_flag(msg, NL80211_ATTR_WIPHY_SELF_MANAGED_REG))
 		goto nla_put_failure;
 
-	return genlmsg_end(msg, hdr);
+	genlmsg_end(msg, hdr);
+	return 0;
 
 nla_put_failure:
 	genlmsg_cancel(msg, hdr);
@@ -6577,7 +6582,8 @@ static int nl80211_send_bss(struct sk_buff *msg, struct netlink_callback *cb,
 
 	nla_nest_end(msg, bss);
 
-	return genlmsg_end(msg, hdr);
+	genlmsg_end(msg, hdr);
+	return 0;
 
  fail_unlock_rcu:
 	rcu_read_unlock();
@@ -6686,7 +6692,8 @@ static int nl80211_send_survey(struct sk_buff *msg, u32 portid, u32 seq,
 
 	nla_nest_end(msg, infoattr);
 
-	return genlmsg_end(msg, hdr);
+	genlmsg_end(msg, hdr);
+	return 0;
 
  nla_put_failure:
 	genlmsg_cancel(msg, hdr);
@@ -11025,7 +11032,8 @@ static int nl80211_send_scan_msg(struct sk_buff *msg,
 	/* ignore errors and send incomplete event anyway */
 	nl80211_add_scan_req(msg, rdev);
 
-	return genlmsg_end(msg, hdr);
+	genlmsg_end(msg, hdr);
+	return 0;
 
  nla_put_failure:
 	genlmsg_cancel(msg, hdr);
@@ -11048,7 +11056,8 @@ nl80211_send_sched_scan_msg(struct sk_buff *msg,
 	    nla_put_u32(msg, NL80211_ATTR_IFINDEX, netdev->ifindex))
 		goto nla_put_failure;
 
-	return genlmsg_end(msg, hdr);
+	genlmsg_end(msg, hdr);
+	return 0;
 
  nla_put_failure:
 	genlmsg_cancel(msg, hdr);