netdev - [PATCH 4/5] net: Make ifindex generation per-net namespace

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Message-ID: <50236C6F.10503@parallels.com>
Date:	Thu, 09 Aug 2012 11:53:19 +0400
From:	Pavel Emelyanov <xemul@...allels.com>
To:	David Miller <davem@...emloft.net>,
	Eric Dumazet <eric.dumazet@...il.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Linux Netdev List <netdev@...r.kernel.org>,
	Ben Hutchings <bhutchings@...arflare.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@...allels.com>
Acked-by: Eric Dumazet <edumazet@...gle.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
--
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