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>

4 files changed, 16 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;
diff --git a/net/core/dev.c b/net/core/dev.c
index 6b6ef14b42f2..4577e6711ec3 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -199,6 +199,11 @@ static struct list_head ptype_all __read_mostly;	/* Taps */
 DEFINE_RWLOCK(dev_base_lock);
 EXPORT_SYMBOL(dev_base_lock);
 
+static inline void dev_base_seq_inc(struct net *net)
+{
+        while (++net->dev_base_seq == 0);
+}
+
 static inline struct hlist_head *dev_name_hash(struct net *net, const char *name)
 {
         unsigned hash = full_name_hash(name, strnlen(name, IFNAMSIZ));
@@ -237,6 +242,9 @@ static int list_netdevice(struct net_device *dev)
         hlist_add_head_rcu(&dev->index_hlist,
                            dev_index_hash(net, dev->ifindex));
         write_unlock_bh(&dev_base_lock);
+
+        dev_base_seq_inc(net);
+
         return 0;
 }
 
@@ -253,6 +261,8 @@ static void unlist_netdevice(struct net_device *dev)
         hlist_del_rcu(&dev->name_hlist);
         hlist_del_rcu(&dev->index_hlist);
         write_unlock_bh(&dev_base_lock);
+
+        dev_base_seq_inc(dev_net(dev));
 }
 
 /*
diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
index ea489db1bc23..5bbdbf0d3664 100644
--- a/net/core/net_namespace.c
+++ b/net/core/net_namespace.c
@@ -129,6 +129,7 @@ static __net_init int setup_net(struct net *net)
 
         atomic_set(&net->count, 1);
         atomic_set(&net->passive, 1);
+        net->dev_base_seq = 1;
 
 #ifdef NETNS_REFCNT_DEBUG
         atomic_set(&net->use_count, 0);
diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index a798fc6f2aa1..99d9e953fe39 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -1032,6 +1032,8 @@ static int rtnl_dump_ifinfo(struct sk_buff *skb, struct netlink_callback *cb)
         s_idx = cb->args[1];
 
         rcu_read_lock();
+        cb->seq = net->dev_base_seq;
+
         for (h = s_h; h < NETDEV_HASHENTRIES; h++, s_idx = 0) {
                 idx = 0;
                 head = &net->dev_index_head[h];
@@ -1043,6 +1045,8 @@ static int rtnl_dump_ifinfo(struct sk_buff *skb, struct netlink_callback *cb)
                                              cb->nlh->nlmsg_seq, 0,
                                              NLM_F_MULTI) <= 0)
                                 goto out;
+
+                        nl_dump_check_consistent(cb, nlmsg_hdr(skb));
 cont:
                         idx++;
                 }