Re: [RFC PATCH] Allow optional module parameters
From: Rusty Russell
Date: Wed Mar 20 2013 - 01:27:28 EST
Lucas De Marchi <lucas.demarchi@xxxxxxxxxxxxxx> writes:
> 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
>>> Fair enough. What about the other approach, then? Always warn if an
>>> option doesn't match (built-in or otherwise) but load the module
>> What does everyone think of this? Jon, Lucas, does this match your
>> 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?
No good ones :(
MODULE_PARM_DESC isn't compulsory, so you can't rely on that to tell you
about option names.
Even if we had a flag, how would you know to set it? I guess you could
try without then try with, and if it works the second time print a
warning about typos. But it's still pretty ugly.
We could implement such a flag with a fake "IGNORE_BAD_PARAMS"
parameter, for example. That would fail nicely on older kernels, too.
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