Re: [RFC PATCH] Allow optional module parameters

Ben Hutchings
2013-03-19T19:40:55Z

On Tue, 2013-03-19 at 13:02 +1030, Rusty Russell wrote:
> Andy Lutomirski <luto@amacapital.net> writes:
> > On Sun, Mar 17, 2013 at 7:24 PM, Rusty Russell <rusty@rustcorp.com.au> wrote:
> >> Andy Lutomirski <luto@amacapital.net> writes:
> >>> On Thu, Mar 14, 2013 at 10:03 PM, Rusty Russell <rusty@rustcorp.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?

I'm not sure why I'm being cc'd on this, though I did recently remove a
module parameter (sfc.rx_alloc_method). For what it's worth:

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

I agree with this.

> Reported-by: Andy Lutomirski <luto@amacapital.net>
> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
[...]

This should also go to stable, so the downgrading issue doesn't continue
to bite people.

Ben.

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Ben Hutchings, Staff Engineer, Solarflare
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