Re: [PATCH net-next] net-loopback: allow lo dev initial state to be controlled

[Dan Williams <dcbw@redhat.com>]

On Thu, 2020-11-12 at 17:08 +0100, Andrew Lunn wrote:
> On Wed, Nov 11, 2020 at 12:43:08PM -0800, Jian Yang wrote:
> > From: Mahesh Bandewar <maheshb@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.
> 
> How useful is lo if it is up, but has no IP address? I don't think
> this change adds the IP addresses does it? So you still need
> something
> inside your netns to add the IP addresses? Which seems to make this
> change pointless?

lo gets addresses automatically these days, no?

$ ip netns add blue
$ ip netns exec blue ip addr
1: lo: <LOOPBACK> mtu 65536 qdisc noop state DOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
$ ip netns exec blue ip link set lo up
$ ip netns exec blue ip addr
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever

Dan