Device driver questions

[michael at maui.cs.ucla.edu]

I have some questions on devices drivers. The system is a ATnT 3b1
(sys5 R2, more or less).
 
#1. I am writting a block driver for this, but it is a slow block driver.
How do I tell the system that I/O operations should be interruptable,
and how should my driver tell that it has been interrupted, what
should I do, etc.

#2. What systems calls is a device driver allowed to do? In particular,
what is the task time allowed to do (in particular, file I/O).

#3. How can I track file descriptors? I.e., if some process opens a
file, and does things (ioctl calls), and then forks or dups that
file descriptor, when my driver is called later I want to be able
to track things that were done on a file descriptor basis, not just
a device basis.

#4. How can I catch write calls made to another device driver?
(If it makes a difference, this would be to a loadable device driver
(the window driver))

			Michael