How do I use a Linux System call from a Linux Kernel Module

Question

I am having some difficulty calling a system call from inside a Linux Kernel Module. The system calls have been tested and work properly from a standard c user space program

Answer 1

Most of system calls uses asmlinkage , which means find the arguments on the stack rather than registers. Make sure that , when you call system call , pass the arguments on stack.

Also lot many system calls just uses copy_from_user. If you pass kernel address into such system call , they do fail.

Answer 2

You can directly call sys_mycall.

#include <linux/module.h>
#include <linux/unistd.h>


static int start_init(void)
{
   long value = sys_mycall (pass_arguments)
   printk("The value is %ld\n",value);

   return 0;
}

static void finish_exit(void)
{
      printk("Done!\n");
}

module_init(start_init);
module_exit(finish_exit);