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

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Date:	Tue, 19 Mar 2013 19:40:51 +0000
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Rusty Russell <rusty@...tcorp.com.au>
CC:	Andy Lutomirski <luto@...capital.net>,
	<linux-kernel@...r.kernel.org>, <linux-kbuild@...r.kernel.org>,
	Jon Masters <jcm@...hat.com>,
	Lucas De Marchi <lucas.demarchi@...fusion.mobi>
Subject: Re: [RFC PATCH] Allow optional module parameters

On Tue, 2013-03-19 at 13:02 +1030, Rusty Russell 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?

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@...capital.net>
> Signed-off-by: Rusty Russell <rusty@...tcorp.com.au>
[...]

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

Ben.

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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