DomU trying to write on an IO Port

DomU trying to write on an IO Port

[Nitin Gupta]

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Hi,

I am running xen-hypervisor over qemu. 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.

-- 
Regards,
Nitin Gupta

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Re: DomU trying to write on an IO Port

[Ian Campbell]

On Mon, 2013-02-18 at 12:31 +0000, Nitin Gupta wrote:
> Hi,
> 
> 
> I am running xen-hypervisor over qemu.

You mean running Xen in a virtual machine provided by qemu? Or are you
talking about the qemu which is associated with an HVM domain under Xen
(i.e. the one running in dom0 or a stub domain).

>  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.
> 
> -- 
> Regards,
> Nitin Gupta
> 
> 

Re: DomU trying to write on an IO Port

[Nitin Gupta]

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I am running Xen in a virtual machine provided by qemu (qemu-system
emulation) without KVM.


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

> On Mon, 2013-02-18 at 12:31 +0000, Nitin Gupta wrote:
> > Hi,
> >
> >
> > I am running xen-hypervisor over qemu.
>
> You mean running Xen in a virtual machine provided by qemu? Or are you
> talking about the qemu which is associated with an HVM domain under Xen
> (i.e. the one running in dom0 or a stub domain).
>
> >  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.
> >
> > --
> > Regards,
> > Nitin Gupta
> >
> >
>
>
>


-- 
Regards,
Nitin Gupta
M.Tech. CSE, IIT Delhi

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Re: DomU trying to write on an IO Port

[Ian Campbell]

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@citrix.com> 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.