Re: [RFC PATCH] Allow optional module parameters

Rusty Russell
2013-03-19T04:55:49Z

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.

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

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;