Re: [RFC PATCH] Allow optional module parameters

From: Andy Lutomirski
Date: Tue Mar 19 2013 - 20:32:36 EST

On Tue, Mar 19, 2013 at 8:26 PM, Lucas De Marchi
<lucas.demarchi@xxxxxxxxxxxxxx> wrote:
> Hi Rusty,
> On Mon, Mar 18, 2013 at 11:32 PM, Rusty Russell <rusty@xxxxxxxxxxxxxxx> wrote:
>> Andy Lutomirski <luto@xxxxxxxxxxxxxx> writes:
>>> On Sun, Mar 17, 2013 at 7:24 PM, Rusty Russell <rusty@xxxxxxxxxxxxxxx> wrote:
>>>> Andy Lutomirski <luto@xxxxxxxxxxxxxx> writes:
>>>>> On Thu, Mar 14, 2013 at 10:03 PM, Rusty Russell <rusty@xxxxxxxxxxxxxxx> 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?


> Lucas De Marchi

Andy Lutomirski
AMA Capital Management, LLC
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