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

[Andrew Evans <andrewe@xxxxxxxxxxxxx>]

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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