linux-kernel - Re: [RFC PATCH] Allow optional module parameters

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Message-ID: <CAMOw1v5AOmy38KNVfxj6OO-U0UCXST50vD0g0W5fEpNfKCpGvg@mail.gmail.com>
Date:	Tue, 19 Mar 2013 21:26:04 -0300
From:	Lucas De Marchi <lucas.demarchi@...fusion.mobi>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	Andy Lutomirski <luto@...capital.net>,
	linux-kernel@...r.kernel.org,
	Ben Hutchings <bhutchings@...arflare.com>,
	linux-kbuild@...r.kernel.org, Jon Masters <jcm@...hat.com>
Subject: Re: [RFC PATCH] Allow optional module parameters

Hi Rusty,

On Mon, Mar 18, 2013 at 11:32 PM, Rusty Russell <rusty@...tcorp.com.au> wrote:
> Andy Lutomirski <luto@...capital.net> writes:
>> On Sun, Mar 17, 2013 at 7:24 PM, Rusty Russell <rusty@...tcorp.com.au> wrote:
>>> Andy Lutomirski <luto@...capital.net> writes:
>>>> On Thu, Mar 14, 2013 at 10:03 PM, Rusty Russell <rusty@...tcorp.com.au> wrote:
>>>>> Err, yes.  Don't remove module parameters, they're part of the API.  Do
>>>>> you have a particular example?
>>>>
>>>> So things like i915.i915_enable_ppgtt, which is there to enable
>>>> something experimental, needs to stay forever once the relevant
>>>> feature becomes non-experimental and non-optional?  This seems silly.
> ...
>>>> Having the module parameter go away while still allowing the module to
>>>> load seems like a good solution (possibly with a warning in the logs
>>>> so the user can eventually delete the parameter).
>>>
>>> Why not do that for *every* missing parameter then?  Why have this weird
>>> notation where the user must know that the parameter might one day go
>>> away?
>>
>> Fair enough.  What about the other approach, then?  Always warn if an
>> option doesn't match (built-in or otherwise) but load the module
>> anyways.
>
> What does everyone think of this?  Jon, Lucas, does this match your
> experience?
>
> Thanks,
> Rusty.
>
> Subject: modules: don't fail to load on unknown parameters.
>
> Although parameters are supposed to be part of the kernel API, experimental
> parameters are often removed.  In addition, downgrading a kernel might cause
> previously-working modules to fail to load.

I agree with this reasoning

>
> On balance, it's probably better to warn, and load the module anyway.

However loading the module anyway would bring at least one drawback:
if the user made a typo when passing the option the module would load
anyway and he will probably not even look in the log, since there's
was no errors from modprobe.

For finit_module we could put a flag to trigger this behavior and
propagate it to modprobe, but this is not possible with init_module().
I can't think in any other option right now... do you have any?


Lucas De Marchi
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