netdev - Re: [PATCH net-next] Revert "net-loopback: set lo dev initial state to UP"

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Message-ID: <20210209102912.2ad7b2ff@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Tue, 9 Feb 2021 10:29:12 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Petr Machata <petrm@...dia.com>
Cc:     <netdev@...r.kernel.org>, Jian Yang <jianyang.kernel@...il.com>,
        <davem@...emloft.net>, Mahesh Bandewar <maheshb@...gle.com>,
        Jian Yang <jianyang@...gle.com>
Subject: Re: [PATCH net-next] Revert "net-loopback: set lo dev initial state
 to UP"

On Tue, 9 Feb 2021 18:52:04 +0100 Petr Machata wrote:
> In commit c9dca822c729 ("net-loopback: set lo dev initial state to UP"),
> linux started automatically bringing up the loopback device of a newly
> created namespace. However, an existing user script might reasonably have
> the following stanza when creating a new namespace -- and in fact at least
> tools/testing/selftests/net/fib_nexthops.sh in Linux's very own testsuite
> does:
> 
>  # set -e
>  # ip netns add foo
>  # ip -netns foo addr add 127.0.0.1/8 dev lo
>  # ip -netns foo link set lo up
>  # set +e
> 
> This will now fail, because the kernel reasonably rejects "ip addr add" of
> a duplicate address. The described change of behavior therefore constitutes
> a breakage. Revert it.
> 
> Fixes: c9dca822c729 ("net-loopback: set lo dev initial state to UP")
> Signed-off-by: Petr Machata <petrm@...dia.com>

Reviewed-by: Jakub Kicinski <kuba@...nel.org>

Thanks!