get all the file_system_type registered in linux kernel

Recently I am learning vfs in kernel. I want to write a kernel module, which can show all the file_system_type registered in linux kernel. But the list head of all the file_system_type - file_systems can't be got through some API! So I check all the file systems in the /proc/filesystems. And use get_fs_type() and file system type name to get the corresponding file_system_type variable. Does someone has easy method to achieve my goal? And how do I read file in the proc file system, for example, /proc/filesystems? Thanks in advance. -mudongliang