Current serial.sys is stable for reading from the
serial port.
Writing works but is synchronous (ie never returns
STATUS_PENDING and you can't use overlapped I/O in Win32)
Flow handling is not implemented (XON/XOFF) Stopping/removing
a serial port when running the system is not implemented yet
A few other things, which are probably not important, except
one (according to
http://www.wd-3.com/archive/SerialFilter.htm):
The WaitMask can be set with IOCTL_SERIAL_SET_WAIT_MASK, but
IOCTL_SERIAL_WAIT_ON_MASK is not implemented yet.
I can take a look at it if you want.
It's committed in revision 23712.