get all the file_system_type registered in linux kernel

[慕冬亮]

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