On Wed, 11 Nov 2020 12:43:08 -0800 Jian Yang wrote:
> From: Mahesh Bandewar <mahe...@google.com>
>
> Traditionally loopback devices comes up with initial state as DOWN for
> any new network-namespace. This would mean that anyone needing this
> device (which is mostly true except sandboxes where networking in not
> needed at all), would have to bring this UP by issuing something like
> 'ip link set lo up' which can be avoided if the initial state can be set
> as UP. Also ICMP error propagation needs loopback to be UP.
>
> The default value for this sysctl is set to ZERO which will preserve the
> backward compatible behavior for the root-netns while changing the
> sysctl will only alter the behavior of the newer network namespaces.
Any reason why the new sysctl itself is not per netns?
> +netdev_loopback_state
> +---------------------
loopback_init_state ?
> +Controls the loopback device initial state for any new network namespaces. By
> +default, we keep the initial state as DOWN.
> +
> +If set to 1, the loopback device will be brought UP during namespace
> creation.
> +This will only apply to all new network namespaces.
> +
> +Default : 0 (for compatibility reasons)
> +
> netdev_max_backlog
> ------------------
>
> diff --git a/drivers/net/loopback.c b/drivers/net/loopback.c
> index a1c77cc00416..76dc92ac65a2 100644
> --- a/drivers/net/loopback.c
> +++ b/drivers/net/loopback.c
> @@ -219,6 +219,13 @@ static __net_init int loopback_net_init(struct net *net)
>
> BUG_ON(dev->ifindex != LOOPBACK_IFINDEX);
> net->loopback_dev = dev;
> +
> + if (sysctl_netdev_loopback_state) {
> + /* Bring loopback device UP */
> + rtnl_lock();
> + dev_open(dev, NULL);
> + rtnl_unlock();
> + }
The only concern I have here is that it breaks notification ordering.
Is there precedent for NETDEV_UP to be generated before all pernet ops
->init was called?
