Since NTFS is a proprietary file system created by Microsoft, how did the ntfs-3g developers manage to create an open source version of the NTFS drivers without referring to the NTFS source code? Or is there some kind of agreement with Microsoft regarding this??
ntfs-3g is the following of the first NTFS driver created back in 1995 by Martin von Löwis.
The driver has been mostly reverse engineered which mean by observing and analyzing the data structure and find a way to correctly handling it.
According to the original project site
The method was roughly:
1 Look at the volume with a hex editor
2 Perform some operation, e.g. create a file
3 Use the hex editor to look for changes
4 Classify and document the changes
5 Repeat steps 1-4 forever
After a long developement and a laborious work, a fork has been created from NTFS-Linux according to the first release note of
ntfs-3g back in 2006:
As part of the Linux-NTFS project, I'm happy to announce my contribution to ntfsmount and libntfs which resulted ntfs-3g, a read-write ntfs driver, capable for unlimited file creation and deletion.
I hope this partial answer help you see how this was born and how it continues to leave.
It's important to note that today this driver is maintained by Tuxera and is no longer an amateur product.
That's right. Reverse engineering.
Reverse engineering is basically looking at patterns for a certain behaviour and expected results and document them in a way that you can reproduce it without even looking at the code.
For example, for windows compatibility network layer for CIFS/SMB (NetBIOS for early versions, AKA as window shares) the Samba project developers used a network sniffer and a packet analyzer in such a way that they documented what those network packages contained for certain operations (like sending a request to the port to list shares) and then simulate the same operation but with their own code implementation, as long as the network packet data send was compatible with what the windows server was expecting.
So NTFS-3g was the same thing, but looking at hard disk behaviour and results, instead of network.