The Linux way to define a filesystems

The code is laid out as a set of "operations"

struct super_operations;
Mount, umount, ...
These are the methods to act on the filesystem as a whole

struct inode_operations;
Mkdir, rmdir, rename, unlink, ...
It is the set of methods that act on the file-tree

struct file_operations;
Open, release, read, write, mmap, ...
The set of methods that act on data proper
And they are different according to the file type