Re: [Xen-users] Creating a paravirtualized guest with Xen 3.4.1 and Centos 5.3 (64bit)

[Martin Troester <TroyMcClure@xxxxxx>]

Andrew,

you are right. Looking into my settings again, I now realize that I just 
gave the wrong parameter to the config file. I used initr where I should 
have been using ramdisk. Arrrrrrgh.
So now my VM boots fine with the second config file as well. It works so 
easy if you do things right ;-)
Now I'll find out if I can get my original problem solved, migrate the 
existing fully virtualized system to a paravirtualizded kernel. Let's see...
Thanks again for your support.

Regards,
Martin

Andrew Evans wrote:
> I think your problem is the lack of xenblk/xennet drivers. Try `cp -pr 
> /lib/modules` to your target VM. I think then you'll be able to boot.
> -Andrew
>
> Martin Tröster wrote:
> > Hi,
> >
> > I have a set of 32bit HVM images running fine under Xen 3.2.1 and Xen 
> > 3.4.1. Due to performance issues with the fully virtualized setup, I 
> > would like to migrate one of those images to a paravirtualized image 
> > to compare the network performance. As I do not have a Xen-aware 
> > kernel for that VM, I thought the best would be to provide one from 
> > outside.
> > Sounds like an easy task, doesn't it? ;-)
> >
> > However, I fail miserably on this task. It just does not work. To get 
> > rid of any side effects, I thought it would be nice to try with a 
> > known-working image.
> > Therefore I got the image Centos 5.3 image from 
> > http://stacklet.com/downloads/images/centos/5.3. And voila, using the 
> > pygrub version works like a charm - I can either log in using xm 
> > console, or ssh. This is the config used:
> > bootloader = "/usr/bin/pygrub"
> > memory = 256
> > name = "centos_pygrub"
> > vif = [ 'bridge=eth0,mac=02:00:00:00:01:86'  ]
> > disk = ['file:image,sda1,w']
> > root = "/dev/sda1"
> > extra = "fastboot"
> >
> > Now, as this kernel appears to be working fine, I thought I'd like to 
> > just take this kernel and initrd out of the known-good vm, and give it 
> > to Xen as parameters. In my naive thinking, this should be the very 
> > same as pygrub is doing - loading the kernel specified in 
> > /boot/grub.conf with initrd and parameters (all taken from the VM 
> > running fine with pygrub):
> > kernel = "vmlinuz"
> > initrd = "initrd"
> > extra = "console=xvc0"
> > root = "/dev/sda1"
> > memory = 256
> > name = "centos_pv"
> > vif = [ 'bridge=eth0,mac=02:00:00:00:01:86'  ]
> > disk = ['file:image,sda1,w']
> >
> > BUT - this fails! The last lines on the command line are:
> >
> > XENBUS: Device with no driver: device/vbd/2048
> > XENBUS: Device with no driver: device/vif/0
> > XENBUS: Device with no driver: device/console/0
> > md: Autodetecting RAID arrays.
> > md: autorun ...
> > md: ... autorun DONE.
> > VFS: Cannot open root device "sda1" or unknown-block(0,0)
> > Please append a correct "root=" boot option
> > Kernel panic - not syncing: VFS: Unable to mount root fs on 
> > unknown-block(0,0)
> > The only obvious difference compared to the previous VM is the line 
> > stating "md: autodetecting RAID arrays.". But why should this very 
> > same kernel, that initializes fine when using pygrub, now start 
> > setting up raid configs? I don't seem to get it, so I really 
> > appreciate some help here, I already spent too long debugging this, I 
> > have no idea what goes wrong here. Does my host config have anything 
> > to do with it (yes, it has a raid)? But if yes, why would it? I did 
> > not build the initrd image myself, it's the one taken from the VM 
> > which booted fine using pygrub...
> > Thanks a lot!
> >
> > Regards,
> > Martin
> >
> > P.S.: The Xen log does not show any error at all, only reports the VM 
> > having crashed.
> > P.P.S.: When I get this running (there's still hope left...), I would 
> > like to understand what's the best option to provide a disk - is it 
> > tap:aio, or file? Any documentation on reasons to choose either the 
> > one or the other?
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