Re: [RFC PATCH] Allow optional module parameters

Jonathan Masters
2013-07-01T16:33:19Z

One caveat. Sometimes we have manufactured parameters intentionally to cause a module to fail. We should standardize that piece.

--
Sent from my iPad

On Jul 1, 2013, at 4:53, Rusty Russell <rusty@rustcorp.com.au> wrote:

> Rusty Russell <rusty@rustcorp.com.au> writes:
>> Lucas De Marchi <lucas.demarchi@profusion.mobi> writes:
>>> Hi Rusty,
>>>
>>> On Mon, Mar 18, 2013 at 11:32 PM, Rusty Russell <rusty@rustcorp.com.au> 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?
>>>>
>>>> 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.
>
> OK, so I've had this patch on the backburner, but noone has come up with
> anything better so I'll queue it into modules-next now.
>
> Thanks,
> Rusty.
>
> 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.
> This may let through a typo, but at least the logs will show it.
>
> Reported-by: Andy Lutomirski <luto@amacapital.net>
> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
>
> diff --git a/kernel/module.c b/kernel/module.c
> index 3c2c72d..46db10a 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -3206,6 +3206,17 @@ out:
> return err;
> }
>
> +static int unknown_module_param_cb(char *param, char *val, const char *modname)
> +{
> + /* Check for magic 'dyndbg' arg */
> + int ret = ddebug_dyndbg_module_param_cb(param, val, modname);
> + if (ret != 0) {
> + printk(KERN_WARNING "%s: unknown parameter '%s' ignored\n",
> + modname, param);
> + }
> + return 0;
> +}
> +
> /* Allocate and load the module: note that size of section 0 is always
> zero, and we rely on this for optional sections. */
> static int load_module(struct load_info *info, const char __user *uargs,
> @@ -3292,7 +3303,7 @@ static int load_module(struct load_info *info, const char __user *uargs,
>
> /* Module is ready to execute: parsing args may do that. */
> err = parse_args(mod->name, mod->args, mod->kp, mod->num_kp,
> - -32768, 32767, &ddebug_dyndbg_module_param_cb);
> + -32768, 32767, unknown_module_param_cb);
> if (err < 0)
> goto bug_cleanup;
>
>