Re: [Xen-users] Extra Probes on xl create

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Wed, 2012-05-30 at 01:15 +0100, Ian wrote:
> Hi All,
> 
> I have two Xen machines, both running 4.12 compiled from source. One is 
> running SL6.2 with a kernel compiled from vanilla source (3.2.0) and the 
> second is using the stock kernel from Ubuntu (3.2.0-23-generic).
> 
> I moved a pv CentOS 5.8 vm from the SL machine to the Ubuntu machine and 
> noticed a difference when starting (i.e. an error)
> 
> "xl -v create" gives...
> 
> 
> SL 6.2
> 
> domainbuilder: detail: xc_dom_allocate: cmdline="ro root=LABEL=/ 
> console=xvc0 ", features="(null)"
> domainbuilder: detail: xc_dom_kernel_mem: called
> domainbuilder: detail: xc_dom_malloc            : 10836 kB
> domainbuilder: detail: xc_dom_do_gunzip: unzip ok, 0x21bbf4 -> 0xa952d8
> domainbuilder: detail: xc_dom_ramdisk_mem: called
> domainbuilder: detail: xc_dom_boot_xen_init: ver 4.1, caps 
> xen-3.0-x86_64 xen-3.0-x86_32p hvm-3.0-x86_32 hvm-3.0-x86_32p 
> hvm-3.0-x86_64
> domainbuilder: detail: xc_dom_parse_image: called
> domainbuilder: detail: xc_dom_find_loader: trying ELF-generic loader ...
> domainbuilder: detail: loader probe OK
> 
> Ubuntu 12.04
> 
> domainbuilder: detail: xc_dom_allocate: cmdline="ro root=LABEL=/ 
> console=xvc0 ", features="(null)"
> domainbuilder: detail: xc_dom_kernel_mem: called
> domainbuilder: detail: xc_dom_malloc            : 10836 kB
> domainbuilder: detail: xc_dom_do_gunzip: unzip ok, 0x21bbf4 -> 0xa952d8
> domainbuilder: detail: xc_dom_ramdisk_mem: called
> domainbuilder: detail: xc_dom_boot_xen_init: ver 4.1, caps 
> xen-3.0-x86_64 xen-3.0-x86_32p
> domainbuilder: detail: xc_dom_parse_image: called
> domainbuilder: detail: xc_dom_find_loader: trying multiboot-binary 
> loader ...
> domainbuilder: detail: loader probe failed
> domainbuilder: detail: xc_dom_find_loader: trying Linux bzImage loader ...
> xc: error: panic: xc_dom_bzimageloader.c:556: 
> xc_dom_probe_bzimage_kernel: kernel is not a bzImage: Invalid kernel
> domainbuilder: detail: loader probe failed
> domainbuilder: detail: xc_dom_find_loader: trying ELF-generic loader ...
> domainbuilder: detail: loader probe OK
> 
> 
> Both boot fine, and it looks like the Ubuntu version is trying to do 
> something extra. I googled the error message and I am not concerned 
> about it as it appears to be a spurious error caused by an extra probe.

That's right, it's spurious. I have an outstanding patch on xen-devel@
to tone it down, it shouldn't be a panic!

> Apart from the SL vs Ubuntu difference, I thought I had the machines 
> pretty similar from a Xen perspective. Can anyone please explain why 
> these extra probes are talking place and what in my (possibly build) 
> environment might have caused this to happen (or indeed cause this *not* 
> to happen on the SL box).

If the kernels being used are identical then I don't know. Are you
booting the kernel from inside the CentOS VM (e.g. via pygrub) or are
you picking it up from the dom0 filesystem?

If the kernels are not identical then the message is probably because
one kernel is a bzImage (often this == pvops) and the other is a
compressed ELF file (often this == classic XenoLinux).

You seem to be building some kernels yourself but FWIW the out of the
box kernel on Ubuntu is pvops while SL and CentOS 5 are both classic.

Ian.



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