rtnl: provide link dump consistency info

This patch adds a change sequence counter to each net namespace
which is bumped whenever a netdevice is added or removed from
the list. If such a change occurred while a link dump took place,
the dump will have the NLM_F_DUMP_INTR flag set in the first
message which has been interrupted and in all subsequent messages
of the same dump.

Note that links may still be modified or renamed while a dump is
taking place but we can guarantee for userspace to receive a
complete list of links and not miss any.

Testing:
I have added 500 VLAN netdevices to make sure the dump is split
over multiple messages. Then while continuously dumping links in
one process I also continuously deleted and re-added a dummy
netdevice in another process. Multiple dumps per seconds have
had the NLM_F_DUMP_INTR flag set.

I guess we can wait for Johannes patch to hit net-next via the
wireless tree.  I just wanted to give this some testing right away.

Signed-off-by: Thomas Graf <tgraf@infradead.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/net/net_namespace.h b/include/net/net_namespace.h
index aef430d779bd..1ab1aec209ac 100644
--- a/include/net/net_namespace.h
+++ b/include/net/net_namespace.h
@@ -65,6 +65,7 @@ struct net {
         struct list_head        dev_base_head;
         struct hlist_head       *dev_name_head;
         struct hlist_head       *dev_index_head;
+        unsigned int            dev_base_seq;   /* protected by rtnl_mutex */
 
         /* core fib_rules */
         struct list_head        rules_ops;