linux-kernel - Re: [PATCH can-next v6] can: add tx/rx LED trigger support

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Message-ID: <5044A547.2010603@pengutronix.de>
Date:	Mon, 03 Sep 2012 14:40:39 +0200
From:	Marc Kleine-Budde <mkl@...gutronix.de>
To:	Fabio Baltieri <fabio.baltieri@...il.com>
CC:	linux-can@...r.kernel.org, linux-kernel@...r.kernel.org,
	Oliver Hartkopp <socketcan@...tkopp.net>,
	Wolfgang Grandegger <wg@...ndegger.com>
Subject: Re: [PATCH can-next v6] can: add tx/rx LED trigger support

On 08/25/2012 12:01 AM, Fabio Baltieri wrote:
> Hello Kurt,
> 
> On Fri, Aug 24, 2012 at 02:42:48PM +0200, Kurt Van Dijck wrote:
>> On Fri, Aug 24, 2012 at 01:28:16PM +0200, Marc Kleine-Budde wrote:
>>> On 08/24/2012 07:10 AM, Kurt Van Dijck wrote:
>>>> Hello,
>>>>
>>>> I find the CAN led triggers an interesting thing.
>>>>
>>>> And then, this scenario fell crossed my mind:
>>>> Imagine I do:
>>>> [insert CAN device: can0]
>>>> $ ip link set can0 name helga
>>>> [insert another CAN device: again 'can0']
>>>>
>>>> Registering 'can0-tx' led trigger will fail for the second CAN device,
>>>> since that led trigger name is already reserved for CAN device 'helga'.
>>> Good point.
> 
> Yep, thanks for pointing that out!
> 
> Interface renaming was something I considered when I first wrote the
> code and I had the mac80211-led driver in mind, as that driver uses the
> phy name and not the netdev one for its triggers.
> 
> The reason why I did not care that much in the end is that on SoC based
> systems trigger-led association is made at probe time, based on data
> either from platform_data or devicetree, so I imagined that once the
> kernel is ported to the board and default triggers are set correctly at
> boot time, the userspace is free to rename CAN interfaces and nobody
> should notice... :^)
> 
> The thing I did not consider are hot-plug interfaces mixed with
> renaming, such as in the case you pointed out - it's probably not really
> common but still possible.
> 
>>>> I'm not sure how to fix such.
>>>> If 'rx' & 'tx' may be combined, reusing the netdev name may be possible?
>>>> Just wild thinking ...
>>>
>>> I think the device's name (not netdev) is unique in the system and
>>> cannot be changed.
>>
>> but may contain several netdev's ...
> 
> Ouch.

The net->ifindex is unique. But it's only an integer. Usually can0 has a
ifindex != 0, so a simple can%d is contra productive here.

Some pointers to related code:
http://lxr.free-electrons.com/source/drivers/base/core.c#L1847
http://lxr.free-electrons.com/source/drivers/base/core.c#L73
http://lxr.free-electrons.com/source/include/linux/device.h#L695

comments?

Marc
-- 
Pengutronix e.K.                  | Marc Kleine-Budde           |
Industrial Linux Solutions        | Phone: +49-231-2826-924     |
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