[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 <***@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)
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[Rusty Russell]

Post by 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.

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

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[Bert Wesarg]

Post by Rusty Russell

Post by 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.

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,
$ 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

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

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