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>

2 files changed, 3 insertions, 7 deletions

diff --git a/include/net/genetlink.h b/include/net/genetlink.h
index 8412508..f24aa83 100644
--- a/include/net/genetlink.h
+++ b/include/net/genetlink.h
@@ -245,9 +245,9 @@ static inline void *genlmsg_put_reply(struct sk_buff *skb,
  * @skb: socket buffer the message is stored in
  * @hdr: user specific header
  */
-static inline int genlmsg_end(struct sk_buff *skb, void *hdr)
+static inline void genlmsg_end(struct sk_buff *skb, void *hdr)
 {
-	return nlmsg_end(skb, hdr - GENL_HDRLEN - NLMSG_HDRLEN);
+	nlmsg_end(skb, hdr - GENL_HDRLEN - NLMSG_HDRLEN);
 }
 
 /**
diff --git a/include/net/netlink.h b/include/net/netlink.h
index d5869b9..e010ee8 100644
--- a/include/net/netlink.h
+++ b/include/net/netlink.h
@@ -490,14 +490,10 @@ static inline struct sk_buff *nlmsg_new(size_t payload, gfp_t flags)
  * Corrects the netlink message header to include the appeneded
  * attributes. Only necessary if attributes have been added to
  * the message.
- *
- * Returns the total data length of the skb.
  */
-static inline int nlmsg_end(struct sk_buff *skb, struct nlmsghdr *nlh)
+static inline void nlmsg_end(struct sk_buff *skb, struct nlmsghdr *nlh)
 {
 	nlh->nlmsg_len = skb_tail_pointer(skb) - (unsigned char *)nlh;
-
-	return skb->len;
 }
 
 /**