[PATCH 4/5 (resend)] net: Make ifindex generation per-net namespace (v2)

[Pavel Emelyanov <xemul@parallels.com>]

>> @@ -62,6 +62,7 @@ struct net {
>>  	struct sock 		*rtnl;			/* rtnetlink socket */
>>  	struct sock		*genl_sock;
>>  
>> +	int			ifindex;
> 
> could you place ifindex right after dev_base_seq : avoid two holes
> and use the same cache line, dirtied in
> list_netdevice()/unlist_netdevice()

Sure! Here it is:

From: Pavel Emelyanov <xemul@parallels.com>
Subject: [PATCH 4/5] net: Make ifindex generation per-net namespace

Strictly speaking this is only _really_ required for checkpoint-restore to
make loopback device always have the same index.

This change appears to be safe wrt "ifindex should be unique per-system"
concept, as all the ifindex usage is either already made per net namespace
of is explicitly limited with init_net only.

There are two cool side effects of this. The first one -- ifindices of
devices in container are always small, regardless of how many containers
we've started (and re-started) so far. The second one is -- we can speed
up the loopback ifidex access as shown in the next patch.

v2: Place ifindex right after dev_base_seq : avoid two holes and use the
    same cache line, dirtied in list_netdevice()/unlist_netdevice()

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
---
 include/net/net_namespace.h |    1 +
 net/core/dev.c              |    4 ++--
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/include/net/net_namespace.h b/include/net/net_namespace.h
index ae1cd6c..6dc3db3 100644
--- a/include/net/net_namespace.h
+++ b/include/net/net_namespace.h
@@ -66,6 +66,7 @@ struct net {
 	struct hlist_head 	*dev_name_head;
 	struct hlist_head	*dev_index_head;
 	unsigned int		dev_base_seq;	/* protected by rtnl_mutex */
+	int			ifindex;
 
 	/* core fib_rules */
 	struct list_head	rules_ops;
diff --git a/net/core/dev.c b/net/core/dev.c
index 3ca300d..1f06df8 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -5221,12 +5221,12 @@ int dev_ioctl(struct net *net, unsigned int cmd, void __user *arg)
  */
 static int dev_new_index(struct net *net)
 {
-	static int ifindex;
+	int ifindex = net->ifindex;
 	for (;;) {
 		if (++ifindex <= 0)
 			ifindex = 1;
 		if (!__dev_get_by_index(net, ifindex))
-			return ifindex;
+			return net->ifindex = ifindex;
 	}
 }
 
-- 
1.7.6.5