Virtual Filesystem R3 - 07/21/03 (the final approach - hopefully :) )

This filesystem is inspried by the virtual filesystem used by Linux. It has one root directory where all other filesystems, devices (as device files) and files are accessed from.

To access files of a filesystem, the filesystem needs to be mounted to the VFS-tree. This is accomplished with the mount-command which calls the VFS-function mount. When mounting a filesystem to the VFS-tree the mount-function needs four parameters: the filesystem source file (usually a device file, but can be a filesystem-imagefile, too), the mount-point (the directory in the VFS-tree where the new filesystem shall be accessed from), the filesystem-type and the mount-options (rw-mode, loop, access-rights etc).

There are (currently) two types of filesystem-sources that can be mounted to the VFS-tree:

1. a device-source

This filesystem-source is a device represented by it«s device-file (usually found in the /dev-directory). tionThe mount-function opens the requested device-file and reads the actual device id from this file (device numbers).

2. a filesystem-imagefile

An imagefile is an exact binary copy of a disk partition including the filesystem data. Thus an imagefile that is stored on any filesystem of the VFS-tree can be mounted into the direcotry tree.

The mount-function

1. open filesystem-sourcefile
2. read first XY bytes and check for special file type (device, pipe etc)
3. if it«s special open the device or pipe and store the struct
4. if it«s no special it must be an image file, check the image«s integrity then
5. store appropriate struct into mountlist (s_device, s_pipe or s_file *)
6. close the file

* this is very useful when keeping the image-file always open until it gets unmounted

The open-function

1. open filesystem-sourcefile
2. read first XY bytes and check for special file type (device, pipe etc)
3. if it«s special open the device or pipe and store the struct
4. if it«s no special it must be a convential file on a filesystem, redirect
the request with the device-struct from the mountlist to the appropriate
filesystem-driver
5. store the appropriate struct in the s_file-struct and return it

Typical device file/pipe file

In a device/pipe file we store a simple struct as binary (subject to change)

   struct s_specialfile {
   	
	char [10] classname;
	union {
		unsigned char devmajor;
		unsigned char pid;
        }
	union {
		unsigned char devminor;
		unsigned char pid2;
	}
   }