[PATCH] kernel/param.c: don't use .max when .num is NULL in param_array_set()

[PATCH] kernel/param.c: don't use .max when .num is NULL in param_array_set()

[Bert Wesarg]

Hello,

there seems to be a bug, at least for me, in kernel/param.c for arrays
with .num == NULL. If .num == NULL, the function param_array_set() uses
&.max for the call to param_array(), wich alters the .max value to the
number of arguments. The result is, you can't set more array arguments as
the last time you set the parameter.

example:

# a module 'example' with
# static int array[10] = { 0, };
# module_param_array(array, int, NULL, 0644);

$ insmod example.ko array=1,2,3
$ cat /sys/module/example/parameters/array
1,2,3
$ echo "4,3,2,1" > /sys/module/example/parameters/array
$ dmesg | tail -n 1
kernel: array: can take only 3 arguments

Patch is against 2.6.12-rc1.

Signed-off-by: Bert Wesarg <wesarg@informatik.uni-halle.de>

--- linux-2.6.12-rc1.orig/kernel/params.c	2005-03-27 14:44:00.000000000 +0200
+++ linux-2.6.12-rc1/kernel/params.c	2005-03-27 14:45:55.000000000 +0200
@@ -314,9 +314,10 @@ int param_array(const char *name,
 int param_array_set(const char *val, struct kernel_param *kp)
 {
 	struct kparam_array *arr = kp->arg;
+	unsigned int temp_num;

 	return param_array(kp->name, val, 1, arr->max, arr->elem,
-			   arr->elemsize, arr->set, arr->num ?: &arr->max);
+			   arr->elemsize, arr->set, arr->num ?: &temp_num);
 }

 int param_array_get(char *buffer, struct kernel_param *kp)

Re: [PATCH] kernel/param.c: don't use .max when .num is NULL in param_array_set()

[Rusty Russell]

On Sun, 2005-03-27 at 14:57 +0200, Bert Wesarg wrote:
> Hello,
> 
> there seems to be a bug, at least for me, in kernel/param.c for arrays
> with .num == NULL. If .num == NULL, the function param_array_set() uses
> &.max for the call to param_array(), wich alters the .max value to the
> number of arguments. The result is, you can't set more array arguments as
> the last time you set the parameter.

Yes.  But this ignores the larger problem, in that the printing routines
need *some* way of telling how many to print.  We could add a new
element for this case, at the price of enlarging the structure a little
for every array parameter.  I think you'll find that with your patch,
the code does this:

	$ insmod example.ko array=1,2,3
	$ cat /sys/module/example/parameters/array
	1,2,3,0,0,0,0,0,0,0

Cheers,
Rusty.
-- 
A bad analogy is like a leaky screwdriver -- Richard Braakman

Re: [PATCH] kernel/param.c: don't use .max when .num is NULL in param_array_set()

[Bert Wesarg]

On Tue, 29 Mar 2005, Rusty Russell wrote:

> On Sun, 2005-03-27 at 14:57 +0200, Bert Wesarg wrote:
> > Hello,
> >
> > there seems to be a bug, at least for me, in kernel/param.c for arrays
> > with .num == NULL. If .num == NULL, the function param_array_set() uses
> > &.max for the call to param_array(), wich alters the .max value to the
> > number of arguments. The result is, you can't set more array arguments as
> > the last time you set the parameter.
>
> Yes.  But this ignores the larger problem, in that the printing routines
> need *some* way of telling how many to print.  We could add a new
> element for this case, at the price of enlarging the structure a little
> for every array parameter.  I think you'll find that with your patch,
> the code does this:
>
> 	$ insmod example.ko array=1,2,3
> 	$ cat /sys/module/example/parameters/array
> 	1,2,3,0,0,0,0,0,0,0

Yes, but in this case you can/will past a num pointer to
module_param_array(), when it is important to know how many arguments are
specified.

greetings,
bert

>
> Cheers,
> Rusty.
> --
> A bad analogy is like a leaky screwdriver -- Richard Braakman
>