I'm not sure I responded on-list, but for the record:

I defined BROKEN_SIGIO (thanks to Brett and Stephen for hints), and
emacs 21.2 now works fine in /coda on NetBSD 1.6.1ish.  This is a
workaround, not a true fix, since SIGIO should really work in
coda-land, but I'm able to get work done now, and can defer the hard
work of grokking the signal handling issues.

        Greg Troxel <gdt_at_ir.bbn.com>