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[Xen-users] Serial port access in HVM (fully virtualized) DomU

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Subject: [Xen-users] Serial port access in HVM (fully virtualized) DomU
From: Hans Rakers <hans@xxxxxxxx>
Date: Tue, 04 Dec 2007 11:59:07 +0100
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Hello xen-users,

Last days i've been pulling my hair on getting ttyS0 (COM1) to work in a HVM DomU. I want to use it for an external faxmodem for use with Hylafax. I've Googled myself crazy and have seen just about every page on this subject :)

My system is CentOS 5.1 with xen-3.0.3-41.el5. I've added xencons=off to grub.conf of DomU and i've added the following to /etc/modprobe.d/blacklist:

blacklist 8250
blacklist 8250_pnp
blacklist serial_core

I can confirm that Dom0 does not claim the serial ports (no mention of it during boot, no modules loaded, xencons off)

My DomU also runs CentOS 5.1. I've added the following to its vm config:

irq = [3, 4]
ioports = ["3f8-3ff", "2f8-2ff"]

Syslog of the DomU mentions the loading of the 8250 module, but no resulting ports:

Serial: 8250/16550 driver $Revision: 1.90 $ 4 ports, IRQ sharing enabled

/proc/ioports of the DomU also doesn't mention the mapped ioports:

[...snip snip...]
01f0-01f7 : ide0
03c0-03df : vga+
03f2-03f5 : floppy
03f6-03f6 : ide0
03f7-03f7 : floppy DIR
0cf8-0cff : PCI conf1
[...snip snip...]

Is this at all possible, or am i overlooking something stupid? Do 'ioports' and 'irq' work with fully virtualized VM's? I've read something earlier on this list at http://lists.xensource.com/archives/html/xen-users/2007-08/msg00838.html which states that it is impossible for HVMs to have direct access to hardware, which is why i ask, before spending another day on this :)

Thanks in advance,

Hans Rakers

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