netdev - RFC: bring UP 'lo' by default after creating new netns

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Message-ID: <CAF2d9jhTcVgLHs_iqw+RRS=WhMtRF0ra5SygGMymuYQUW6HP0A@mail.gmail.com>
Date:   Thu, 29 Jun 2017 16:57:39 -0700
From:   Mahesh Bandewar (महेश बंडेवार) 
        <maheshb@...gle.com>
To:     Eric Dumazet <edumazet@...gle.com>, ebiederm@...ssion.com,
        adobriyan@...il.com, David Miller <davem@...emloft.net>,
        xiyou.wangcong@...il.com
Cc:     linux-netdev <netdev@...r.kernel.org>
Subject: RFC: bring UP 'lo' by default after creating new netns

Creation of new network namespace is almost always followed up by
bringing up the loopback device.

        ip netns add foo
        ip -netns foo link set lo up

I'm not sure if there are any consequences of bringing the device UP
at the creation of network-namespace.

thanks,
--mahesh..

diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
index 2178db8e47cd..ac0e86c9a17f 100644
--- a/net/core/net_namespace.c
+++ b/net/core/net_namespace.c
@@ -428,6 +428,11 @@ struct net *copy_net_ns(unsigned long flags,
                net_drop_ns(net);
                return ERR_PTR(rv);
        }
+       /* Set the loopback device UP */
+       rtnl_lock();
+       dev_open(net->loopback_dev);
+       rtnl_unlock();
+
        return net;
 }