netdev - Re: [PATCH] net: add operstate for vcan and dummy

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Date:   Thu, 2 Jun 2022 20:39:04 -0700
From:   Stephen Hemminger <stephen@...workplumber.org>
To:     Kaarel Pärtel <kaarelp2rtel@...il.com>
Cc:     Wolfgang Grandegger <wg@...ndegger.com>,
        Marc Kleine-Budde <mkl@...gutronix.de>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, linux-can@...r.kernel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: add operstate for vcan and dummy

On Thu,  2 Jun 2022 11:19:29 +0300
Kaarel Pärtel <kaarelp2rtel@...il.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.
> 
> The kernel considers the unknown state to be the same as up:
> https://elixir.bootlin.com/linux/latest/source/include/linux/netdevice.h#L4125
> 
> However for users this creates confusion:
> https://serverfault.com/questions/629676/dummy-network-interface-in-linux
> 
> The change in this patch is very simple. When the interface is set up, the
> operational state is set to IF_OPER_UP.
> 
> Signed-off-by: Kaarel Pärtel <kaarelp2rtel@...il.com>
> ---
>  drivers/net/can/vcan.c | 1 +
>  drivers/net/dummy.c    | 1 +
>  2 files changed, 2 insertions(+)
> 
> 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)
>  
>  	dev->netdev_ops		= &vcan_netdev_ops;
>  	dev->needs_free_netdev	= true;
> +	dev->operstate = IF_OPER_UP;
>  }
>  
>  static struct rtnl_link_ops vcan_link_ops __read_mostly = {
> 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)
>  
>  	dev->min_mtu = 0;
>  	dev->max_mtu = 0;
> +	dev->operstate = IF_OPER_UP;
>  }
>  
>  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.