2010.01.02
The 2.4 kernel seems to leave lots of stubs for
future system calls. We can just take 240, 241, 242 and make them what we want.
This sub directory 242 adds
  241 with a return parameter and
  242 with a return parameter and a single input parameter.

<asm/unistd.h>     Just use the existing system call numbers (240, 241, 242)
/usr/src/linux/arch/i386/kernel/entry.S   Insert my syscalls in the list

The Kernel can read paramers from user space and return stack values to
user space, but returning a reference parameter value to user space is
tricky and handled in another example. See Nutt lab 5.

2010.01.02
The following modifications are needed to add the simplest system call with
no parameter and no return value. The sub directory syscall-240 has the
code and discusses how to add simplest system call with no 
parameters and no return value.

<asm/unistd.h>     Just use the existing system call number 240

/usr/src/linux/arch/i386/kernel/entry.S
Insert my_syscall at 240 replacing futex


2010.01.02
This Nutt lab 5 is about adding system calls and requires re-compiling the
kernel.