Assignment 2 SO: Stdio Library

This assignment was about reimplemening some of the basic functions that come with the stdio.h. In this implementation buffering is present.

I really enjoyed doing this. I saw a bit of the the dirty stuff the is underneath the functions that we use everyday just to open and read from a file. There was a lot to learn.

General approach

• The SO_FILE mainly has a buffer and a lot of fields that maintain informationa about the state of the buffer, keep track whether or not an error occured or the EOF was reached, the struct is associated with a file or a process.
• The functions are well documented, but the main points are:
  • so_fputc writes to the buffer, and the buffer is flushed into the file descriptor only if it is full
  • so_fgetc tries to read the whole buffer so that a next call would read from the buffer and not make a syscall
  • so_fwrite is implemented with so_fputc
  • so_fread is implemented with so_fgetc
  • There are 3 variables that keep track of the internal state of the buffer: one that knows what the last operaion was and two pointers: _left_ptr and _right_ptr that are the bounds of the buffer in which you have real data
  • so_ftell is implemented with so_fseek

Difficulties

This assignment was fun to work on, but I faced some difficulties along the way:

1. The buffer was a pain to work with. Reading has to flush the data that was written and writing after a read has to clear the buffer.
2. Also keeping track of the data read into the buffer that never got to be accessed with a so_fgetc or so_fread had to be done in order not to ruin the actual location of the so_fseek/so_ftell

How to use

• include so_stdio.h in your project and use the functions available
• OR
• use make and that will create a shared library libso_stdio.so