nvi dying with "Resource temporarily unavailable"

[Stephen McKay]

Since I upgraded to FreeBSD 4.8 (from 4.5) I've noticed occasional failures
of nvi.  It will suddenly die as a key is pressed, emitting:

Error: input: Resource temporarily unavailable

and you are staring at your command prompt.

I googled for this message and found that people here and there have been
complaining of this since about FreeBSD 4.2, but that absolutely none of
them have received a reply.

What's going on here?  Down in the bowels of nvi a read of the pty returns
EAGAIN and that is treated as fatal.  This should only occur with read() if
the input is non-blocking, and as far as I can tell it isn't.

So, is this a nvi bug (read() returning EAGAIN should be non-fatal)?  Is
this a pty bug (read() incorrectly returning EAGAIN)?  Perhaps it could be
even an xterm bug?  (Since I also upgraded to the XFree86 4.x series when I
upgraded to FreeBSD 4.8 and maybe those other folks were early adopters).

Any ideas?

Stephen.