Serial console problems with stable/8

David Evans dave.evans55 at
Mon Sep 13 11:36:02 UTC 2010

 I can confirm there is much weirdness with the uart on 8-STABLE.

I'm using FBSD in several virtual machines on Parallels Desktop.

It is possible to set the serial port on the VM to output to a file on the host OS

I try something like   'cat file > /dev/cuad0  on FBSD 7 and 8. This works
on 7 but hangs after the first few kB on 8.

Next I try a login on the guest OS.  I set one VM to be a server and the other
a client. I connect the two VM's serial ports together via a socket on the
host OS. I also start a login on the server VM's serial port.

With both VMs running 7, I can login using kermit on the client. No amount
of trying gets flow control of any type to work, but at least it does not hang.
The lack of flow control means that much output is lost.

With both VMs running 8, I can login, just about, but attempting to edit
a file or do a long ls listing results in a hang. Flow control does not work
in either the RTS/CTS or XON/XOFF modes.

Next, I try kernel debugging using kgdb via serial link between two
VMs running 8. I'm surprised to find that it works quite well with
no hangs.  Presumably this is because the kgdb protocol only sends
small amounts of data at a time or perhaps it runs at a low level, as
mentioned earlier in this thread.  I have not tried this with 7.

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