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Date:   Thu, 2 Jun 2022 20:39:04 -0700
From:   Stephen Hemminger <stephen@networkplumber.org>
To:     Kaarel =?UTF-8?B?UMOkcnRlbA==?= <kaarelp2rtel@gmail.com>
Cc:     Wolfgang Grandegger <wg@grandegger.com>,
        Marc Kleine-Budde <mkl@pengutronix.de>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>, linux-can@vger.kernel.org,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] net: add operstate for vcan and dummy
Message-ID: <20220602203904.65f7261f@hermes.local>
In-Reply-To: <20220602081929.21929-1-kaarelp2rtel@gmail.com>
References: <20220602081929.21929-1-kaarelp2rtel@gmail.com>
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On Thu,  2 Jun 2022 11:19:29 +0300
Kaarel P=C3=A4rtel <kaarelp2rtel@gmail.com> wrote:

> The idea here is simple. The vcan and the dummy network devices
> currently do not set the operational state of the interface.
> The result is that the interface state will be UNKNOWN.
>=20
> The kernel considers the unknown state to be the same as up:
> https://elixir.bootlin.com/linux/latest/source/include/linux/netdevice.h#=
L4125
>=20
> However for users this creates confusion:
> https://serverfault.com/questions/629676/dummy-network-interface-in-linux
>=20
> The change in this patch is very simple. When the interface is set up, the
> operational state is set to IF_OPER_UP.
>=20
> Signed-off-by: Kaarel P=C3=A4rtel <kaarelp2rtel@gmail.com>
> ---
>  drivers/net/can/vcan.c | 1 +
>  drivers/net/dummy.c    | 1 +
>  2 files changed, 2 insertions(+)
>=20
> diff --git a/drivers/net/can/vcan.c b/drivers/net/can/vcan.c
> index a15619d883ec..79768f9d4294 100644
> --- a/drivers/net/can/vcan.c
> +++ b/drivers/net/can/vcan.c
> @@ -162,6 +162,7 @@ static void vcan_setup(struct net_device *dev)
> =20
>  	dev->netdev_ops		=3D &vcan_netdev_ops;
>  	dev->needs_free_netdev	=3D true;
> +	dev->operstate =3D IF_OPER_UP;
>  }
> =20
>  static struct rtnl_link_ops vcan_link_ops __read_mostly =3D {
> diff --git a/drivers/net/dummy.c b/drivers/net/dummy.c
> index f82ad7419508..ab128f66de00 100644
> --- a/drivers/net/dummy.c
> +++ b/drivers/net/dummy.c
> @@ -133,6 +133,7 @@ static void dummy_setup(struct net_device *dev)
> =20
>  	dev->min_mtu =3D 0;
>  	dev->max_mtu =3D 0;
> +	dev->operstate =3D IF_OPER_UP;
>  }
> =20
>  static int dummy_validate(struct nlattr *tb[], struct nlattr *data[],

Normally carrier state is propogated to operstate by linkwatch.
You may need to add a call for that.