mount system call for nullfs

[Alfonso Sabato Siciliano]

Hello,

I would use "mount" system call

 int mount(const char *type, const char *dir, int flags, void *data);

to mount a nullfs, the problem is about *data;

Where can I find docs? Example? Code?

(the implementation of mount_nullfs(8) uses nmount syscall so it is not
usefulI;

I put a string "/mount_from_dir" then errno = 45, so I think it should be a
struct)

Thanks
Alfonso