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>

2 files changed, 13 insertions, 6 deletions

diff --git a/net/core/dev.c b/net/core/dev.c
index f91abf800161..3ca300d85271 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;
 
diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index db037c9a4c48..34d975b0f277 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -1812,8 +1812,6 @@ replay:
                         return -ENODEV;
                 }
 
-                if (ifm->ifi_index)
-                        return -EOPNOTSUPP;
                 if (tb[IFLA_MAP] || tb[IFLA_MASTER] || tb[IFLA_PROTINFO])
                         return -EOPNOTSUPP;
 
@@ -1839,10 +1837,14 @@ replay:
                         return PTR_ERR(dest_net);
 
                 dev = rtnl_create_link(net, dest_net, ifname, ops, tb);
-
-                if (IS_ERR(dev))
+                if (IS_ERR(dev)) {
                         err = PTR_ERR(dev);
-                else if (ops->newlink)
+                        goto out;
+                }
+
+                dev->ifindex = ifm->ifi_index;
+
+                if (ops->newlink)
                         err = ops->newlink(net, dev, tb, data);
                 else
                         err = register_netdevice(dev);