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[Xen-users] Serial Passthrough broken in Debian Wheezy?


I just discovered a strange bug with serial passthrough in xen 4.1 on
Debian Wheezy. The Dom0 has a GSM modem connected to serial port. The
serial port is passed through to a DomU with options 'irq = [ 4 ]' and
'ioports = [ '3f8-3ff ]'.

This worked as expected on Debian Squeeze with Xen 4.0 and Linux kernel
2.6.32 (both for Dom0 and DomU). On Debian Wheezy with Xen 4.1 and
Linux kernel 3.2.0 the passthrough seems to work as well (/dev/ttyS0
appears in dmesg of DomU), but something is wrong. The GSM modem
doesn't behave as expected. The smstools daemon errors out with 'Cannot
open serial port /dev/ttyS0, error: Function not implemented'.

It took me hours to find the difference, but it seems like the guest
(domU) kernel is the problem. The setup keeps working when Dom0 is
upgraded to Debian Wheezy with Xen 4.1 and linux kernel 3.2.0. It even
keeps working if the DomU userland is upgraded to Debian Wheezy. Only
if I upgrade the DomU linux kernel to 3.2.0 from Wheezy as well,
smstools stops working.

I don't expect this to be a smstools bug. More likely, something
regarding serial pass through functions of xen is broken in 3.2.0
kernel from Debian Wheezy.

Did anybody else discover similar issues yet?

Kind regards,

PS: I'm not subscribed to pkg-xen-devel@xxxxxxxxxxxxxxxxxxxxxxx, please
cc me on that list.

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