It appears that the "compact" flavor has no support for serial ports.
I grepped through the package listing for "compact" without finding
anything with "serial" in its name. I extracted the serial driver
generic_serial.o from the ide kernel package, and inserted it into the
compact kernel, but the symptoms remain the same: the device special
file appears to be made correctly by mknod (as indicated by an ls -l
listing, which shows the correct major and minor numbers; but
attempting to configure the port with setserial still produces "No such
device".) Apparently some part of the kernel the serial driver talks
to is missing.
Probably I could have avoided all this trouble by trying the "vanilla"
flavor to start with; but Chapter 5 of the Installation manual gives no
indication that serial support is missing from "compact"; it just talks
about other less-basic driver categories. So I suggest that this issue
be dealt with in the section on "Choosing a kernel".
-- A. T. Young