Re: [Xen-users] Accessing /dev/ttyI0 in guest domain not possible?

[Mark Williamson <mark.williamson@xxxxxxxxxxxx>]

> Now I started up my xenU domain which does not show anything about found
> ISDN cards, but I am not worried as I don't see any message about network
> cards either which work perfectly.

The default configuration uses a virtual network card - network traffic gets 
sent via dom0, which owns the *real* network card.

> But when starting my Asterisk server in the xenU domain I get some errors:
> Jul  3 18:10:36 ERROR[865]: Unable to register channel '/dev/ttyI0'
> Jul  3 18:10:36 WARNING[865]: chan_modem.so: load_module failed, returning
> -1 Jul  3 18:10:36 WARNING[865]: Loading module chan_modem.so failed!
>
> So it looks that an unpriviliged domain cannot access my ISDN card?

The XenU kernel won't support any real hardware devices, only Xen's virtual 
devices.

> Digging further, I decided to boot a xen0 domain as guest instead of xenU.
> Now my ISDN card is recognized although not installed(?)

> HiSax: AVM PCI driver Rev. 1.29.2.4
> FritzPCI: No PCI card found
> HiSax: Card AVM Fritz PnP/PCI not installed !
>
> Asterisk doesn't complain anymore although I am not sure if it works...
>
> Does anyone know why xenU is not allowed to access my ISDN /dev/ttyI0?

You need to give the domain direct access to the ISDN card.  This is important 
because only one domain can own a PCI card at once.  Multiple drivers 
fighting over a PCI card will end in tears...

You need to hide the PCI device from dom0 so that it doesn't try to drive it: 
add "physdev_dom0_hide=(xx.yy.z)" to Xen's commandline, substituting the 
config address of your card (you can find this in the output of "lspci").

When you boot, check "xm dmesg" for an explicit line from Xen saying that it's 
hiding the PCI device.  If there isn't one then something's wrong - you'll 
have to debug this first.

Once hiding the device works, you need to give the domain access to it.  You 
need to add this to the config file - the syntax for this is (I think) 
described in the user manual.

Once you've done those things, boot the xen0 kernel in the domain and it 
should work.  Let us know if you get stuck.

Cheers,
Mark

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