I am trying to add a system under linux-2.6.28+.
I can successfully do this by adding the system call code to the kernel source tree.

But, since it will take a relative long time to compile the kernel,
I would like to put the real work into a loadable linux module.
Therefore, I am trying to do the following tricks:

----------------------------------------
long (*my_call_ptr) (int i) = NULL;
EXPORT_SYMBOL(my_call_ptr);

asmlinkage long sys_mycall(int i)
{
if (my_call_ptr)
return my_call_ptr(i);
else
return -ENOSYS;
}
----------------------------------------

However I get the following warnings:

warning: data definition has no type or storage class
warning: type defaults to ‘int’ in declaration of ‘EXPORT_SYMBOL’
warning: parameter names (without types) in function declaration

Does this mean that EXPORT_SYMBOL will not support pointer kinds of variables.
And anyone have any clues on how to pass the function pointer to a kernel
module so that I can don't have to recompile kernel whenever I make any changes
to my custom system call.

Thanks.