netdev - Re: [PATCH 1/3] ifb: make device count build-time configurable

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Date:	Tue, 12 Jan 2016 15:54:40 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	stephen@...workplumber.org
Cc:	jhs@...atatu.com, lkundrak@...sk, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] ifb: make device count build-time configurable

From: Stephen Hemminger <stephen@...workplumber.org>
Date: Tue, 12 Jan 2016 10:44:37 -0800

> On Tue, 12 Jan 2016 07:55:22 -0500
> Jamal Hadi Salim <jhs@...atatu.com> wrote:
> 
>> On 16-01-12 06:56 AM, Lubomir Rintel wrote:
>> > The devices can be created at run-time for quite some time already and the
>> > load-time device creation collides with attempts to create the device of
>> > the same name:
>> >
>> >    # rmmod ifb
>> >    # ip link add ifb0 type ifb
>> >    RTNETLINK answers: File exists
>> >
>> > This is pretty much the same situation as was with the block loop devices
>> > which was solved by adding a build-time configuration that the
>> > distributions could use as they deem fit while keeping the default for
>> > compatibility.
>> >
>> > Let's do that here as well.
>> >
>> > Signed-off-by: Lubomir Rintel <lkundrak@...sk>
>> 
>> I guess module options are frowned upon. so:
> 
> I would prefer that this were done with a module parameter, the same as dummy.
> Only developers build their own configured kernels. Having the value set later
> at module load time is preferable.

I like this even less, it means tools behave significantly differently
based upon what module options were passed to the kernel.

Module options really should not change kernel behavior like this..