netdev - Re: [PATCH net v3 1/2] rtnetlink: allow to set iface down before enslaving it

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Date: Fri, 5 Jan 2024 12:59:24 +0100
From: Jiri Pirko <jiri@...nulli.us>
To: Nicolas Dichtel <nicolas.dichtel@...nd.com>
Cc: "David S . Miller" <davem@...emloft.net>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Eric Dumazet <edumazet@...gle.com>, Phil Sutter <phil@....cc>,
	David Ahern <dsahern@...nel.org>, netdev@...r.kernel.org,
	stable@...r.kernel.org
Subject: Re: [PATCH net v3 1/2] rtnetlink: allow to set iface down before
 enslaving it

Thu, Jan 04, 2024 at 05:42:59PM CET, nicolas.dichtel@...nd.com wrote:
>The below commit adds support for:
>> ip link set dummy0 down
>> ip link set dummy0 master bond0 up
>
>but breaks the opposite:
>> ip link set dummy0 up
>> ip link set dummy0 master bond0 down

It is a bit weird to see these 2 and assume some ordering.
The first one assumes:
dummy0 master bond 0, dummy0 up
The second one assumes:
dummy0 down, dummy0 master bond 0
But why?

What is the practival reason for a4abfa627c38 existence? I mean,
bond/team bring up the device themselfs when needed. Phil?
Wouldn't simple revert do better job here?


>
>Let's add a workaround to have both commands working.
>
>Cc: stable@...r.kernel.org
>Fixes: a4abfa627c38 ("net: rtnetlink: Enslave device before bringing it up")
>Signed-off-by: Nicolas Dichtel <nicolas.dichtel@...nd.com>
>Acked-by: Phil Sutter <phil@....cc>
>Reviewed-by: David Ahern <dsahern@...nel.org>
>---
> net/core/rtnetlink.c | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
>diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
>index e8431c6c8490..dd79693c2d91 100644
>--- a/net/core/rtnetlink.c
>+++ b/net/core/rtnetlink.c
>@@ -2905,6 +2905,14 @@ static int do_setlink(const struct sk_buff *skb,
> 		call_netdevice_notifiers(NETDEV_CHANGEADDR, dev);
> 	}
> 
>+	/* Backward compat: enable to set interface down before enslaving it */
>+	if (!(ifm->ifi_flags & IFF_UP) && ifm->ifi_change & IFF_UP) {
>+		err = dev_change_flags(dev, rtnl_dev_combine_flags(dev, ifm),
>+				       extack);
>+		if (err < 0)
>+			goto errout;
>+	}
>+
> 	if (tb[IFLA_MASTER]) {
> 		err = do_set_master(dev, nla_get_u32(tb[IFLA_MASTER]), extack);
> 		if (err)
>-- 
>2.39.2
>
>