Posix serial port reading

Hi Chris

I am the one trying to get the ELO serial touch screen driver working under
XFree86 in QNX. I suggested the change with making reading from the serial
port non-blocking. You are right that making reading from the serial port
wastes a lost of CPU time - I can see everything slows down. I tried to
lower VMIN to 1 - but no difference.

Now there is one thing that I don’t understand - when using the ELO touch
screen driver under XFree86/QNX and not making reading from the serial port
non-blocking - XFree86 event processing seems to hang. For instance if you
type something in a xterm it will not show up until you press the touch
screen a couple of times - i.e. XFree86 gets past reading from the serial
port. Is it necessary for the function which read_input points at - to
normally return or can it be blocking?