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

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Message-ID: <5616ee6f15c2b9da73d23bcc23eca5befc824abe.camel@redhat.com>
Date:   Thu, 12 Nov 2020 13:54:28 -0600
From:   Dan Williams <dcbw@...hat.com>
To:     Andrew Lunn <andrew@...n.ch>, Jian Yang <jianyang.kernel@...il.com>
Cc:     davem@...emloft.net, kuba@...nel.org, netdev@...r.kernel.org,
        Mahesh Bandewar <maheshb@...gle.com>,
        Jian Yang <jianyang@...gle.com>
Subject: Re: [PATCH net-next] net-loopback: allow lo dev initial state to be
 controlled

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@...gle.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