netdev - Re: How to avoid getting ndo_open() immediately after probe

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Message-ID: <YalKSIlxgt1utNOk@lunn.ch>
Date:   Thu, 2 Dec 2021 23:35:52 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Lino Sanfilippo <LinoSanfilippo@....de>
Cc:     Arijit De <arijitde@...vell.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: How to avoid getting ndo_open() immediately after probe

On Thu, Dec 02, 2021 at 09:29:21PM +0100, Lino Sanfilippo wrote:
> 
> Hi,
> 
> On 02.12.21 at 19:11, Arijit De wrote:
> > Hi,
> >
> > I have handled the probe() and registered the netdev structure using register_netdev().
> > I have observed in other opensource driver(i.e. Intel e1000e driver) that ndo_open() gets called only when we try to bring up the interface (i.e. ifconfig <ip> ifconfig eth0 <ip-addr> netmask <net-mask> up).
> > But in my network driver I am getting ndo_open() call immediately after I handle the probe(). It's a wrong behavior, also my network interface is getting to UP/RUNNING state(as shown below) even without any valid ip address.
> 
> There is nothing wrong here. As soon as you register the netdevice with the kernel it is available
> for userspace and userspace is free to bring it up. This may happen immediately after registration,
> so your driver has to be prepared for this.
> Its absolutely fine to bring up a network device without any ip address assigned.

And if you are using NFS root, the kernel can actually call ndo_open()
before register_netdev() even completes.

This is a common bug i look for in new drivers, register_netdev()
pretty much has to be the last thing done inside the probe function.

       Andrew