linux-kernel - Re: [PATCH] can: rename LED trigger name on netdev renames

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Message-ID: <20120907071934.GB37685@macbook.local>
Date:	Fri, 7 Sep 2012 09:19:34 +0200
From:	Kurt Van Dijck <kurt.van.dijck@....be>
To:	Fabio Baltieri <fabio.baltieri@...il.com>
Cc:	Oliver Hartkopp <socketcan@...tkopp.net>,
	Marc Kleine-Budde <mkl@...gutronix.de>,
	Wolfgang Grandegger <wg@...ndegger.com>,
	linux-kernel@...r.kernel.org, linux-can@...r.kernel.org
Subject: Re: [PATCH] can: rename LED trigger name on netdev renames

On Thu, Sep 06, 2012 at 10:46:00PM +0200, Fabio Baltieri wrote:
> On Thu, Sep 06, 2012 at 09:31:07PM +0200, Oliver Hartkopp wrote:
> > >> +
> > >> +/*
> > >> + * NETDEV rename notifier to rename the associated led triggers too
> > >> + */
> > >> +static int can_led_notifier(struct notifier_block *nb, unsigned long msg,
> > >> +			void *data)
> > >> +{
> > >> +	struct net_device *netdev = (struct net_device *)data;
> > >> +	struct can_priv *priv = netdev_priv(netdev);
> > > 
> > > That's the main problem, which I also got stuck into when I did my first
> > > can-led implementation.  As LED structures are in netdev's private data,
> > > you can only use it if your driver is based on the can-dev API, and
> > > there are no way to be sure of that if you get outside driver's code
> > > itself.
> > > 
> > > This would give problems with vcan, slcan, and probabily other
> > > non-mainlined drivers.
> > 
> > 
> > Do you think, this is really a problem?
> > 
> > If a driver decides not to use the can-dev framework it has to implement own
> > solutions or just adopt can-dev.
> 
> Agreed, but this still means that we can't assume that
> netdev_priv(netdev) to a netdev where netdev->type == ARPHRD_CAN points
> to a struct can_priv, right?

It remains a problem for vcan & slcan.
I tend to start looking at how netlink deals with it.
I see 2 options:
* Invent a new flag for netdev->features, like NETIF_F_CANDEV, to be assigned
  at http://lxr.free-electrons.com/source/drivers/net/can/dev.c#L464

* test for the rtnl_link_ops:
  We put a function can_priv_safe(netdev) in driver/net/can/dev.c that tests
  netdev->rtnl_link_ops == &can_link_ops, like in
  http://lxr.free-electrons.com/source/drivers/net/can/dev.c#L751
  and for candev based drivers, it returns a can_priv*, otherwise NULL.
  I'll prepare something early next week ...

Kind regards,
Kurt
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