Registering the File Systems
Figure: Registered File Systems
When you build the Linux kernel you are asked if you want each of the supported
When the kernel is built, the file system startup code contains calls to
the initialisation routines of all of the built in file systems.
Linux file systems may also be built as modules and, in this case, they may
be demand loaded as they are needed or loaded by hand using insmod.
Whenever a file system module is loaded it registers itself with the kernel and unregisters
itself when it is unloaded.
Each file system's initialisation routine registers itself with the Virtual File System
and is represented by a file_system_type data structure
which contains the name
of the file system and a pointer to its VFS superblock read routine. The figure above
shows that the file_system_type data structures
are put into a list pointed at by the file_systems pointer.
Each file_system_type data structure contains the following information:
- Superblock read routine
- This routine is called by the VFS when an
instance of the file system is mounted,
- File System name
- The name of this file system, for example ext2,
- Device needed
- Does this file system need a device to support? Not all
file system need a device to hold them. The /proc file system,
for example, does not require a block device,
You can see which file systems are registered by looking in at /proc/filesystems.
For example, on my system it looks like this: