2010.01.11
I can't believe it worked. But it did. You can replace a system call
with any darn thing!

2010.01.11
This syscall module replaces three system calls and demonstrates some
parameter passing. I'm passing a string in user space to kernel space.
I don't know if this works because strings are special and are put on
the stack, or if the kernel can access a string in user space. Probably
the former case.

The next thing to do is to try to pass a buffer into the kernel. Probably
won't work. How would the kernel read from user address space. Nutt
discuses the way to do this with memcpy and access_ok (verify_area).

I'm only passing a stack integer back into user space. This example
does not show how to pass a reference parameter to the kernel for
the kernel to change and thus pass back.

2010.01.10

  insmod ./mod-syscall-hello.o    insert the module
  lsmod                           see if the modules has loaded
  tail /var/log/syslog            see module load message
  ./mod-syscall-test-retparm      run the syscall test program
  tail /var/log/syslog            see module enter call and leave message
  rmmod mod-syscall-hello         unload module
  lsmod                           see if the modules has unloaded
  tail /var/log/syslog            see module unload message. Read all the
                                    messages produced by this module.

2010.01.10
Second version is simple call with a printk and a return parameter.
The observable results are in /var/log/syslog if the module was
actually loaded and in the test file results.