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yakrofs: Virtual Read-only File System

Yakrofs is a small virtual read-only file system for application development. It is intended for use in applications which have a need for a large number of resources stored in files with fast retrieval; ideal, for example, for game development, where hundreds of textures and sound samples must be organized well and retrievable with a high degree of efficiency.

To this end, yakrofs provides the following services:

  • A set of "virtual file system" objects which allow user-definable file systems. Two are provided: one which uses a standard file system directory tree, and one which uses a zip file.
  • A composite file system into which virtual file systems can be "mounted" in different locations. This allows for an extremely flexible setup where, for example, a zip file could be mounted as the root of the file system (/) but a directory could be mounted as a subtree (/images/main_character), which can ease the process of testing new resources without having to do a full build of application resources.
  • A single, simple handle-based C-callable interface (currently only 8 functions) which simplifies use of the library from other languages besides C.
Currently portions of yakrofs are written in C++, meaning that libstdc++ must be linked with your project. However, the API is entirely callable by C programs, so there is no worry about "corrupting" your C source code with C++.


Here is the sample program provided with the library, which gives a very basic view of some yak_rofs features:

#ifndef YAK_ROFS_H
#include "yak_rofs.h"


  This is a simple program meant to show how the yak_rofs
  library can be used to open and read files from a virtual file

print_buffer( char* buffer, int size )
  int i;
  for ( i = 0; i < size; ++i )
      putchar( buffer[ i ] );
  putchar( '\n' );

print_file( char* filename )
  h = yak_rofs_open_handle( filename );
  if ( yak_rofs_is_valid_handle( h ) )
      print_buffer( yak_rofs_handle_buffer( h ), 
		    yak_rofs_handle_size( h ) );
      puts( "Unable to open " );
      puts( filename );
      puts( "\n" );

int main( int arg_count, char** arg_vector )
  /* first, mount the current directory as root and print the test text */
  yak_rofs_mount( ".", "/" );
  puts( "With current directory mounted as root, printing test_text.txt:\n" );
  print_file( "/test_text.txt" );

  /* now, unmount the current directory as root, mount the zip file as root, */
  /* and do the same thing. */
  yak_rofs_umount( "/" );
  yak_rofs_mount( "test.zip", "/" );
  puts( "\n\nWith test.zip mounted as root, printing test_text.txt:\n" );
  print_file( "/test_text.txt" );
With different files called "test.txt" (one in the current directory and one in a zip file named "test.zip", this produces the following output:
With current directory mounted as root, printing test_text.txt:

This is the text stored in the filesystem version of test_text.txt

With test.zip mounted as root, printing test_text.txt:

This is the text stored in the zip file version of test_text.txt


Yakrofs is currently not released in package form, as there are some elements that need to be fixed (for example, if you open a handle from a rofs mounted in the main tree, unmount the rofs, and then attempt to use the handle, you will get undefined behaviour--not good). Feel free to examine the cvs tree at the sourceforge prokect page at http://sourceforge.net/projects/yakrofs.

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