Subject: Re: [PATCH 1/2] net: Allow to create links with given ifindex

From: [email-masked] (Eric W. Biederman)
Date: Mon, 30 Jul 2012 03:49:53 -0700

Pavel Emelyanov <[email-masked]> writes:

> 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). The question what to do with pre-created devices such
> as lo or sit fbdev is open, but for manually created devices this can be 
> solved by this patch.

Have you walked through and found the locations where we still rely on
ifindex being globally unique?

Last time I was working in this area there were serveral places where
things were indexed by just the interface index.

I susepct it might be easier to generate hotplug events at restart time
saying someone removed and added an identical set of network devices.
Certainly for physical hardware that needs to happen, because things
like mac addresses will change.

Eric

> Signed-off-by: Pavel Emelyanov <[email-masked]>
>
> ---
>
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 0ebaea1..5966e2f 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -5533,7 +5533,12 @@ 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 334b930..76e19aa 100644
> --- a/net/core/rtnetlink.c
> +++ b/net/core/rtnetlink.c
> @@ -1801,8 +1801,6 @@ replay:
>  			return -ENODEV;
>  		}
>  
> -		if (ifm->ifi_index)
> -			return -EOPNOTSUPP;
>  		if (tb[IFLA_MAP] || tb[IFLA_MASTER] || tb[IFLA_PROTINFO])
>  			return -EOPNOTSUPP;
>  
> @@ -1828,10 +1826,14 @@ 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);
> --
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