A Question Concerning Device Drivers

[Greg Pasquariello X1190]

In article <2879 at watale.waterloo.edu>, watmelon at watale.waterloo.edu (Mech. Eng. Robotics Group) writes:
> In System V, is the cpass/passc combination the only way to pass data
> between a user's buffer and a character driver?
> It seems to be a bit of a waste of time to copy data one character at a time
> when you could probably do some kind of block copy.
> Are there other ways of passing the data?

No. Yes.

No, it is not the only way, Yes there are other ways.

The kernel routines copyin() and copyout() copy a specified number of bytes
from (to) the user space.  They are called as follows:

	int copyin(from,to,n)
	char	 *from,to;
	unsigned n;

	copy a specified number of bytes from user space to kernel space.
	returns 0 if successful, otherwise -1.
	

	int copyout(from,to,n)
	char	 *from,to;
	unsigned n;

	copy a specified number of bytes from kernel space to user space.
	returns 0 if successful, otherwise -1.


There are other routines that access user text space, or user data space,
but the two shown above are the two used most often.