bsd versus linux device drivers

[vehemens]

In linux drivers, there is a one to one relationship to an open and a calling 
argument structure called struct file.  It provides a private data pointer 
that allows the driver to preserve unique state information across other 
calls such as read/write/ioctl/mmap/close etc.

For bsd drivers, my understanding there is not an equivalent.  As a result it 
is not possible to preserve different state information for multiple opens by 
the same thread of the same device major/minor #'s.

Is this correct, or did i miss something?