Hang in tcdrain(3) after write(3)
I'm testing some software on DragonFly. There's not much to it. It
talks to the modem, and sends an ATZ and then reads the response.
Linux, FreeBSD, NetBSD, OpenBSD and OS X are OK.
My test rig is DragonFly 5.6-RELEASE x86_64 (fully patched) with a
USR5637 modem, https://www.amazon.com/gp/product/B0013FDLM0. The modem
is located at /dev/cuaU0.
DragonFly hangs on the call to tcdrain(3). Looking at the man page I
don't see any special handling. Cf.,
Attached is the reproducer. The trace is:
Setting tty options
Waiting for write <<-- call to tcdrain(fd)