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

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Message-ID: <CALCETrWLc2b+M7CP7oQVh3a03C2UqM4-MmXCN_Lcrm=QPzBwDA@mail.gmail.com>
Date:	Tue, 19 Mar 2013 20:36:16 -0400
From:	Andy Lutomirski <luto@...capital.net>
To:	Lucas De Marchi <lucas.demarchi@...fusion.mobi>
Cc:	Rusty Russell <rusty@...tcorp.com.au>,
	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

On Tue, Mar 19, 2013 at 8:32 PM, Andy Lutomirski <luto@...capital.net> wrote:
> On Tue, Mar 19, 2013 at 8:26 PM, Lucas De Marchi
> <lucas.demarchi@...fusion.mobi> wrote:
>> 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?
>
> Have a different finit_module return value for "successfully loaded,
> but there were warnings" perhaps?

Never mind.  I was thinking that finit_module was new in 3.9.

--Andy
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