Recently we had the need to have a Xen domU interact with a device attached to the serial port of it’s dom0 host. It’s not as easy to setup as as one would think! Here’s a quick howto. We used CentOS 5.3.

Stop Xen from grabbing the serial port on boot for its own console

Add “xencons=off” as a kernel argument to your dom0 kernel

Stop your dom0 from loading the serial port modules

Edit /etc/modprobe.d/blacklist, and add the following lines:

blacklist 8250
blacklist 8250_pnp
blacklist serial_core

Reboot

Restart the dom0

Add IRQ/Interrupt passthru config to your domU config

Add the following lines to your domU VM config:

addirq = [ 4 ]
ioports = [ "3f8-3ff" ]

Shut down and restart the domU

Run “modprobe 8250″ on the domU to insert the module – you should now have access to your dom0′s serial port!

(You might want to add “modprobe 8250″ to /etc/rc.local, so that the module is added on startup)

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2. How to convert a (CentOS 5) VMWare image to Xen
3. How to generate logs from your jabberd2 server using Bandersnatch