net: Allow to create links with given ifindex

Currently the RTM_NEWLINK results in -EOPNOTSUPP if the ifinfomsg->ifi_index
is not zero. I propose to allow requesting ifindices on link creation. This
is required by the checkpoint-restore to correctly restore a net namespace
(i.e. -- a container).

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 6 insertions, 1 deletions

diff --git a/net/core/dev.c b/net/core/dev.c
index f91abf80016..3ca300d8527 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -5579,7 +5579,12 @@ int register_netdevice(struct net_device *dev)
                 }
         }
 
-        dev->ifindex = dev_new_index(net);
+        ret = -EBUSY;
+        if (!dev->ifindex)
+                dev->ifindex = dev_new_index(net);
+        else if (__dev_get_by_index(net, dev->ifindex))
+                goto err_uninit;
+
         if (dev->iflink == -1)
                 dev->iflink = dev->ifindex;