Figure: Registered File Systems
When you build the Linux kernel you are asked if you want each of the supported file systems. 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. Figure 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:
ext2 nodev proc iso9660