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We are using Linux + KVM + Qemu with libvirt on our servers to manage virtual WIndows 2008 Servers. The Host is Ubuntu 11.04.

The point is on one of our Windows server 2008 guest, we need to connect a dial-up modem. After connecting the modem to the Host, we found that it was connected to /dev/ttyS0. We did checked that the modem was recognized using

echo atdt3333333 > /dev/ttyS1

Server .xml configuration contains

<serial type='pty'>
  <target port='0'/>
<serial type='dev'>
  <source path='/dev/ttyS0'/>
  <target port='1'/>
<console type='pty'>
  <target type='serial' port='0'/>

Now, launching our virtual server, Windows doesn't see any COM port at all, and therefore doesn't see the modem ( all sort of virsh define / stop / start ... had been done )

Does anyone know how to achieve this ?

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This seems to be an issue within libvirt or Qemu. I have not had much opportunity to delve into which specifically is creating the issue. There does seem to be a ticket open regarding it with RedHat, however it was opened back in March and is still marked new. This is likely not a high priority issue. REF:

I also have a Windows based service that requires the use of a serial port for communication with the parent that cannot be utilized currently due to this.

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