Raw vs. block device. I'm confused.

[ron%brl-vgr at sri-unix.UUCP]

From:      Ron Natalie <ron at brl-vgr>

It depends on both the driver and the device as to what exactly is
allowed during RAW IO.  When the read is initiated it is never (unless
someone has really messed up the driver) set up to do more than what the
user asks for.  Generally, what happens is u.u_count is just stuck in
the byte count register (after making conversion to words or negative
as required by the device).

Most of the tape drivers issue an error if the Physical record size is
greater than the dma size (the size asked to read).

-Ron