Re: [Xen-devel] DomU trying to write on an IO Port

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Mon, 2013-02-18 at 14:12 +0000, Nitin Gupta wrote:
> I am running Xen in a virtual machine provided by qemu (qemu-system
> emulation) without KVM.

Please don't top post.

> On Mon, Feb 18, 2013 at 7:16 PM, Ian Campbell <Ian.Campbell@xxxxxxxxxx> wrote:

>         
>         >  Now while running domU I want to write on an IO port, which I'll be
>         > handling inside Qemu. Basically, this is a communication mechanism 
> for
>         > me to communicate with qemu. I am writing on port number '0x378' as 
> a
>         > root user using "outl" function. But when I run this code in domU, 
> it
>         > does not reach qemu.
>         >
>         > So my question is: Is there  some mechanism in xen which handles
>         > writing on IO ports and in case its not a valid IO Port then just
>         > discards the write.

It should be pretty obvious that I/O operations performed by guests are
by default virtualised and not passed to the underlying hardware (which
is qemu in this case).

If you want a guest to be able to access real hardware then you need to
configure it appropriately.  In this case by using the "ioports"
directive in your guest configuration file (see xl.cfg(5)).

Ian.




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