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RE: [Xen-users] RE: RE: can XEN be extended ?

To: "Andy Smith" <andy@xxxxxxxxxxxxxx>, xen-users@xxxxxxxxxxxxxxxxxxx
Subject: RE: [Xen-users] RE: RE: can XEN be extended ?
From: "Petersson, Mats" <Mats.Petersson@xxxxxxx>
Date: Mon, 29 Jan 2007 16:42:51 +0100
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Thread-topic: [Xen-users] RE: RE: can XEN be extended ?
 

> -----Original Message-----
> From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx 
> [mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Andy Smith
> Sent: 29 January 2007 14:29
> To: xen-users@xxxxxxxxxxxxxxxxxxx
> Subject: Re: [Xen-users] RE: RE: can XEN be extended ?
> 
> On Mon, Jan 29, 2007 at 05:48:09AM -0800, anant wrote:
> > You are not getting what i am trying to ask..
> 
> No, you are not getting the answers.
> 
> > The drivers which we want to add retrieves additional 
> hardware info from the
> > system like for instance fan speed. 
> > Here i am not asking how to write drivers, Drivers are 
> already developed
> > here but at the moment they are supported on Windows OS by 
> retreieving
> > additional info from WMI(which WMI doesnt retrieve itself) 
> in windows.

Now, that's a much more clear question, which is why I've been asking
for more details several times. I can explain what you need to do here,
although the answer may not actually be what you wanted to hear... 

> > 
> > So similarly, we want to include those drivers in Linux or 
> Xen (which ever
> > is appropriate) to retrieve those additional info like fan 
> speed, sys temp n
> > all.
> 

As far as I know, Linux tool/drivers in "lmsensors" do this fine. 

However, WMI -> Windows Management Instrumentation, which isn't part of
the Linux system architecture. 

You have a few choices:
1. Use tools available in Linux to monitor your machines. This is the
EASY solution. Most likely, there's no need to do anything other than
learn some new tools here.

2. Add "sensor" hardware material to QEMU and cross-reference that with
the lmsensors drivers in Linux. That way, you can "pretend" that Windows
reads the real hardware, but it's actually just reading the data from
lmsensors via Linux. You will need to "map" the right devices from your
QEMU model to the real hardware - but with the right level of
configuration, you should be able to translate the ACTUAL hardware
measurement to the a virtual sensor even if they are not compatible -
for example, you can implement a temperature monitor that delivers
degrees C (or F), whilst you're actually reading from one that delivers
0.1 degrees C in some way, but dividing he actual number from the sensor
by 10. [It shouldn't be too hard to have a integer multiplier/divisor
and offset for each sensor. Just as an example, if a sensor delivers
degrees Fahrenheit, you'd have an offset of -32, a multiplier of 5 and a
divisor of 9]. 

Here you can make use of many sensors available to Linux and make a
unified interface to Windows. But expect to spend several weeks
understanding how QEMU works, lmsensors work, and how to tie the two
together. 

Tools for this is the same ones that you need for normal Linux
development or building Xen. 

3. Write WMI drivers - not easy for sure - and some work would be needed
to even get to the actual hardware from a virtual machine - there's
currently no interface for this in Xen, so you'd have to extend Xen
itself as well as writing drivers in Windows. Adding complication to
this is that you'd have to support the exact right hardware that is on
the motherboard(s) used, with the correct WMI interface that is used by
your upper-layer WMI software. 

You'll need a Windows DDK. That's the easy bit. You'll also need to
understand how to modify Xen in certain ways, and how to 

On a scale of 1-10 of difficulty (1 = easy, 10=impossible), I'd put:
1. Difficulty 2.
2. Difficulty 7.
3. Difficulty 10 (probably more like 20 => double impossible).

[Also bear in mind that this scale is probbably a log2 scale]

[Note that WMI also supports a bunch of metrics from ordinary drivers,
such as disk throughput from a hard-disk driver, and such. These would
be supported in the regular WMI as long as you use standard Windows
drivers]. 

> If you can include them in Linux now then you should be able to
> include them in your xen-patched Linux dom0 kernel, since it is
> still Linux and this is where all other drivers are.
> 
> > At the moment i am not sure about what all drivers we want 
> to add but that
> > doesnt really matter as my question is just to know wether 
> we can add our
> > own drivers or not ?
> 
> Yes, to Linux.  The Xen dom0 kernel is just a Linux kernel with Xen
> patches applied.  it is still Linux.  Drivers are written for Linux.
> You need to write drivers for Linux.

You can certainly add drivers to the Windows domain - but you can't
arbitrarily access hardware from the HVM domain, so you can't REALLY get
any data from the hardware unless you also manage to find a way to poke
holes onto the real hardware, and this can have some 
> 
> Mkae your drivers work in plain vanilla Linux.  Then apply Xen
> patches.  They will likely apply cleanly, or with only minor
> conflicts if your devices are quite self contained.  Then your
> drivers should work in Xen dom0.
> 
> > If yes then is there any SDK for XEN or how can we achieve that.
> 
> This is not a xen question hence a xen sdk is irrelevant.

Technically, the Xen SDK is all the tools you need to build Xen, which
is described by XenSource someplace - but Andy is correct, it's not
really a relevant question to solve your actual problem. 

--
Mats
> 
> Cheers,
> Andy
> 



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