Modifying The System Calls Dispatch Table (Cont.)

As you can see, the code up to here is quite simple. Ofcourse, we should store the original symbol's value in a static variable, so we can restore it during module_cleanup. Otherwise, The next invocation of this system call would fail miserably.

Note also that our phony system call returns a negative value as an error code. This value (in its positive form) will be placed into the global 'errno' variable of the program executing our system call. This "magic" is performed by the C library.