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Re: [Xen-users] multiple dom0s (was: Re: [Xen-devel] ragarding xen in sl

To: "P, Namitha" <Namitha.P@xxxxxx>
Subject: Re: [Xen-users] multiple dom0s (was: Re: [Xen-devel] ragarding xen in sles10)
From: Mark Williamson <mark.williamson@xxxxxxxxxxxx>
Date: Mon, 10 Dec 2007 01:59:02 +0000
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> I loaded pciback module using modprobe and tried to unbind a pci device
> (IDE controller with pci id --00:1f.1) from PIIX_IDE and bind it to
> pciback. But it is giving error " write error: no such device".

Please remember that you shouldn't try and do this with a device you need to 
use in dom0.  You can only do it with "spare" devices that dom0 doesn't need 
to use in order to run (e.g. the IDE controller with dom0's disk attached 
can't be passed through).  Whilst you're playing around with PCI device 
assignment you would ideally use a testing machine that you don't care about, 
in case you get something wrong.  Don't learn this stuff on an important 
machine if you can help it!

If you want to pass a device through you need to make sure that a normal 
driver in domain 0 does not grab it, otherwise pciback won't be able to seize 
it.  This is quite a common problem, since the hotplug routines are very good 
at loading the "real" device driver automatically, which is usually what you 
want - but not in this case!

To make sure pciback does get the device you can do one of the following:

a) follow the instructions in section 1.ii at 
to manually unbind the device from the current driver and rebind to pciback
b) use the instructions in section 2 at the wiki page to modify modprobe.conf 
to make sure that pciback gets a chance to grab the device before the normal 
driver for that device does
c) compile pciback statically into the kernel and then put a pciback.hide 
directive onto your kernel command line and reboot

I'd start off with a).  Using the instructions on the wiki page you can 
manually unbind the device from whatever its current driver is.  In this 
particular case I think the following command should do that for you:

echo -n "0000:00:1f.1" > "/sys/bus/pci/devices/0000:00:1f.1/driver/unbind"

That command is just a shorthand for what the instructions on the wiki do.

Then issue your other commands again:

> I am using following command to bind the device....
>  echo -n 0000:00:1f.1 > /sys/bus/pci/drivers/pciback/new_slot
>  echo -n 0000:00:1f.1 > /sys/bus/pci/drivers/pciback/bind

and see if this works better.


> Why it is giving such error?
> Thanks and regards
> Namitha
> -----Original Message-----
> From: M.A. Williamson [mailto:maw48@xxxxxxxxxxxxxxxx] On Behalf Of Mark
> Williamson
> Sent: Sunday, 9 December 2007 7:48 AM
> To: P, Namitha
> Cc: xen-users@xxxxxxxxxxxxxxxxxxx
> Subject: [Xen-users] multiple dom0s (was: Re: [Xen-devel] ragarding xen
> in sles10)
> Hi Namitha,
> I hope you don't mind but I've copied my reply onto xen-users for public
> visibility.
> > I am trying to create two privileged domains for better
> performance.....
> > I have set up XEN on sles10 sp1. Created VMs on that.
> >
> > Is it possible to create two domain0's? If it is possible how can we
> > make them to manage VMs.
> >
> > I tried a lot to get document on such topics...but I failed to get
> such
> > document.
> dom0 is much like a domU but it is special in a number of ways.  Two
> important
> ways are:
> 1) can access the real hardware - by default dom0 owns all the real
> hardware
> in the system
> 2) can manage other domains
> Number 1 can be extended to domUs using the pciback / pcifront drivers.
> This
> allows you to dedicate PCI devices to PV domUs.  If you want, you can
> set
> these domUs to be "backends" for certain devices, so that they export
> their
> devices as virtual disks or virtual network interfaces to other domUs,
> just
> like dom0 does.  Or they can just use the devices themselves to improve
> performance.  Giving a domain this ability means that you are trusting
> it as
> much as dom0.
> A more restricted form of this would be to just dedicate, say, a serial
> port
> to a domain.  There's basic support so that HVM domains can be given
> dedicated access to USB devices.  And in the xen-unstable tree it's now
> possible to dedicate PCI devices to HVM domUs - and isolate them so they
> can't damage the system.
> Number 2 is currently reserved only for dom0 and there's no way of
> allowing
> another domain to share this function.
> There are lots of possibilities here, depending on what you're trying to
> achieve.
> Cheers,
> Mark
> > -----Original Message-----
> > From: M.A. Williamson [mailto:maw48@xxxxxxxxxxxxxxxx] On Behalf Of
> Mark
> > Williamson
> > Sent: Monday, 3 December 2007 9:26 AM
> > To: xen-devel@xxxxxxxxxxxxxxxxxxx
> > Cc: P, Namitha
> > Subject: Re: [Xen-devel] ragarding xen in sles10
> >
> > Hi there,
> >
> > If you google around a bit you may find some backup scripts that
> people
> > have
> > hacked up...  I can't think of a specific project you'd go to off the
> > top of
> > my head.
> >
> > > I am new to xen . I need to develop one project that will back up
> > > virtual machine from host. Is there any "script which will support
> >
> > this"
> >
> > > in host. Or any script which is used to list files of virtual
> machines
> > > in the host..........please help me in this regards
> >
> > You could parse the config file to figure out what disk files are used
> > by the
> > VM.  Or you could use the xenstore-* (e.g. xenstore-ls) commands to
> read
> > details from Xenstore regarding what the paths of the virtual disks
> are.
> > Or, more simply, you could just adopt a naming strategy for your
> > domain's
> > virtual disks based on their config file name / hostname.  And then
> just
> > code
> > your backup scripts to understand that (e.g. domain with "hostname"
> has
> > config file /etc/xen/hostname and disk /vm-disks/hostname.disk).
> It'll
> > be
> > site-specific but if it works for you, that's what counts.
> >
> > Personally, I just rsync backup the contents of /mnt/vm/, which
> contains
> > all
> > my VM's virtual disks (having shut the VMs down first).  I also
> > rsync /etc/xen/ to my backup device.  This doesn't record which disk
> > belongs
> > to which VM but it does make it easy to restore the whole lot at once
> > (just
> > rsync them back).  If I ever need to restore a particular VM I can do
> it
> > manually without to much hassle.
> >
> > Actually, I've been working on a much more advanced backup script for
> > backing
> > up VMs in a home / smaller deployment environment.  I'm waiting on
> word
> > from
> > my employers regarding whether I can release this publically.  For
> > anyone
> > interested, there's some details at
> > http://www.cl.cam.ac.uk/~maw48/vm-backup-pictures/ - but don't hold
> your
> > breath for it to be released because it could take a long while to get
> > permission, if it's allowed at all.
> >
> > Cheers,
> > Mark

Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!

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