netlink: add NETLINK_BROADCAST_ERROR socket option

This patch adds NETLINK_BROADCAST_ERROR which is a netlink
socket option that the listener can set to make netlink_broadcast()
return errors in the delivery to the caller. This option is useful
if the caller of netlink_broadcast() do something with the result
of the message delivery, like in ctnetlink where it drops a network
packet if the event delivery failed, this is used to enable reliable
logging and state-synchronization. If this socket option is not set,
netlink_broadcast() only reports ESRCH errors and silently ignore
ENOBUFS errors, which is what most netlink_broadcast() callers
should do.

This socket option is based on a suggestion from Patrick McHardy.
Patrick McHardy can exchange this patch for a beer from me ;).

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Acked-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/linux/netlink.h b/include/linux/netlink.h
index 51b09a1f46c3..1e6bf995435c 100644
--- a/include/linux/netlink.h
+++ b/include/linux/netlink.h
@@ -103,6 +103,7 @@ struct nlmsgerr
 #define NETLINK_ADD_MEMBERSHIP  1
 #define NETLINK_DROP_MEMBERSHIP 2
 #define NETLINK_PKTINFO         3
+#define NETLINK_BROADCAST_ERROR 4
 
 struct nl_pktinfo
 {